Pre-Excavation Grouting in Rock Tunelling

Pre-Excavation Groutingin Rock Tunneling

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Knut F. GarsholM.Sc. Engineering Geology

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Acknowledgement

The author wishes to thank colleagues within MBT Underground Construction (a Division of DegussaConstruction Chemicals) for their assistance and support in the preparation of this publication. Specialthanks are due to Hans Olav Hognestad for his valuable input and corrections based on his extensivehands-on experience; to Sam Spearing (now with a new employer) for his polite and necessarylanguage corrections and general content suggestions; to Tom Melbye for approving the project,proof reading and other suggestions and his continuous push to move forward to printing. A numberof external friends and contacts have also contributed in many ways to the final product.

Pre-Excavation Groutingin Tunneling

Knut F. GarsholM.Sc Engineering Geology

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� Copyright MBT International Underground Construction Group,Division of MBT (Switzerland) Ltd., 2003

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Index

1. INTRODUCTION 91.1 Reasons for grouting in tunneling 91.2 Short explanation of the subject 91.3 Scope of the book 101.4 Traditional cement based grouting technology 111.5 Rationale for the increase in the use of pressure grouting 121.6 Some comments on Post-grouting 141.7 New time-saving methods and materials technology 15

2. GROUTING INTO ROCK 172.1 Particular features of rock (compared to soil) 172.2 Handling of rock conductivity contrast 21

2.2.1 Description of typical grout to refusal procedure 212.2.2 Stable grout of micro-cement using dual stop criteria 222.2.3 Comparison of the two procedures 22

2.3 “Design” of grouting in rock tunnels 232.4 Fluid transport in rock 252.5 Practical basis for injection works in tunnelling 272.6 Grout quantity prognosis 29

3. FUNCTIONAL REQUIREMENTS 313.1 Influence of tunnelling on the surroundings 313.2 Conditions inside the tunnel 33

3.2.1 Calculation of water ingress to tunnels and tightness ofgrouted zone 34

3.3 Special cases 363.4 Requirements and ground water control during construction phase 373.5 Measurement of water ingress tot he tunnel 38

4. CEMENT-BASED GROUTS 394.1 Basic properties of cement grouts 39

4.1.1 Cement particle size, fineness 394.1.2 Bentonite 434.1.3 Rheological behavior of cement grouts 444.1.4 Pressure stability of cement grouts 454.1.5 Use of high injection pressure 464.1.6 Grout setting characteristics 46

4.2 Durability of cement injection in rock 474.3 Accelerators for cement injection 48

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5. CHEMICAL GROUTS 505.1 Polyurethane grouts 51

5.1.1 General 515.1.2 MBT - PU products 525.1.3 Pumping equipment 53

5.2 Silicate grouts 535.3 MBT colloidal silica 545.4 Acrylic grouts 54

5.4.1 MBT acrylic products 555.5 Epoxy resins 565.6 Combined systems of silicate and acrylic materials 565.7 Bitumen (asphalt) 56

6. BORE HOLES IN ROCK 596.1 Top hammer percussive drilling 596.2 Down the hole drilling machines 616.3 Rotary low speed drilling 626.4 Rotary high speed core drilling 626.5 Example solution for drill and blast excavation (tunnels and shaft) 62

6.5.1 Drilling of injection holes 636.5.2 Packer placement 646.5.3 Water pressure testing 646.5.4 Choice of injection materials 646.5.5 Mix design for Rheocem grouting 656.5.6 Accelerated cement grout 656.5.7 Injection pressure 656.5.8 Special measures 666.5.9 Injection procedure 676.5.10 Injection records 676.5.11 Cement hydration 676.5.12 Other relevant issues 68

6.6 Solutions for TBM excavation 696.6.1 The Oslo sewage tunnel system 696.6.2 The Hong-Kong sewage tunnel system 716.6.3 Comments on drilling and injection equipment 71

6.7 Cleaning of holes 726.8 Packers 74

6.8.1 Mechanical packers (expanders) 746.8.2 Disposable packers 766.8.3 Hydraulic packers 776.8.4 Standpipes techniques 786.8.5 Tube-a-manchet 79

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6.9 Probing ahead of the face 806.9.1 Normal approach 816.9.2 Computer supported logging 82

7. HIGH PRESSURE GROUND WATER CONDITIONS 857.1 Basic problem 857.2 Features that add to the problem 857.3 Consequences for the contractor 857.4 Consequences for the owner 867.5 Methods 867.6 Practical procedure in high risk areas 87

7.6.1 Pumping system 877.6.2 Probe drilling 887.6.3 Injection 887.6.4 Special issues 88

7.7 Practical aspects 897.8 Equipment 907.9 Examples 90

7.9.1 Kjela Hydropower Scheme (south-central Norway) 907.9.2 Ulla Forre Hydropower Scheme (south-west Norway) 917.9.3 Holen Hydropower Scheme (south-central Norway) 91

7.10 Summary of lessons learned 92

8. EQUIPMENT FOR CEMENT INJECTION 948.1 Mixing equipment 948.2 Grout pumps 978.3 Complete systems 988.4 Recording of grouting data 99

9. OUTLINE METHOD STATEMENT FOR PRE-GROUTING IN ROCK 1019.1 Drilling 101

9.1.1 General 1019.1.2 Flushing of boreholes for injection 1019.1.3 Length of boreholes 1029.1.4 Number of holes, hole direction 1029.1.5 Placing of packers 103

9.2 Injection 1039.2.1 General 1039.2.2 Mixing procedure 1039.2.3 Use of an accelerator in the grout 1049.2.4 Injection pressure 1069.2.5 Injection procedure 1069.2.6 Injection records 107

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9.3 Setting of grout, time until next activity 1079.4 Drilling of control holes 1089.5 Measuring of water ingress in excavated parts of the tunnel 1089.6 Decision making flowchart, example criteria (Figure 9.1) 108

10. EXAMPLES OF RESULTS ACHIEVED 11110.1 General 11110.2 What is achievable 11110.3 Comparing shallow and deep tunnels 112

10.3.1 Some shallow hard rock tunnels in Sweden 11210.3.2 Some shallow tunnels in the Oslo area 11410.3.3 Deep situated tunnels 115

10.4 Sedrun access tunnel Alp Transit project, Switzerland 11510.5 Bekkestua Road Tunnel, Oslo Norway 116

10.5.1 Practical execution in the Bekkestua Tunnel 11610.6 The Bjoroy sub-sea road tunnel 117

10.6.1 The project 11710.6.2 The problem 11710.6.3 The solution 11810.6.4 Results 119

10.7 The Orment Project (the snake) Stockholm, Sweden 12010.7.1 The project 12010.7.2 Tunnel data 12010.7.3 Some general information 121

10.8 Limerick main drainage water tunnel, Ireland 12110.8.1 The project 12110.8.2 The problem 12110.8.3 The solution 12210.8.4 Results 122

10.9 The Kilkenny main drainage tunnel, Ireland 12310.9.1 The project 12310.9.2 The problem 12310.9.3 The solution 12310.9.4 Results 124

10.10 West Process Propane Cavern project (WPPC), Norway 12410.10.1 The project 12410.10.2 The problem 12510.10.3 The solution 12510.10.4 The results 125

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11. MBT INJECTION MATERIALS 12611.1 The Rheocem range of tunnel grouting cements 12611.2 Polyurethane grouts 129

11.2.1 MEYCO MP 355 1K 12911.2.2 MEYCO MP 355 A3 130

11.3 Acrylate resin grouts 13111.3.1 MEYCO MP 301 131

11.4 Special product on silica basis 13211.4.1 MEYCO MP 320 Colloidal Silica 132

12. REFERENCES 136

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1. INTRODUCTION

1.1 Reasons for grouting in tunneling

Tunnel excavation involves a certain risk of encountering unexpected groundconditions. One of the risks is the chance of hitting large quantities of highpressure ground water. Also smaller levels of ground water ingress can causeproblems in the tunnel or in the surroundings. Water is the most frequent reasonfor grouting in tunnels. Ground water ingress can be controlled or handled bydrainage, pre-excavation grouting and post-excavation grouting.

Rock or soil conditions causing stability problems for the tunnel excavation isanother reason for grouting. Poor and unstable ground can be improved byfilling discontinuities with a grout material with sufficient strength and adhesion.

1.2 Short explanation of the Subject

Pressure grouting in rock is executed by drilling boreholes of suitable diameter,length and direction into the rock material, placing packers near the boreholeopening (or some other means of providing a pressure tight connection to theborehole), connecting a grout conveying hose or pipe between a pump and thepacker and pumping a prepared grout by overpressure into the cracks andjoints of the rock surrounding the boreholes.

In tunnel grouting, there are two fundamentally different situations to be aware of:

• Pre-excavation grouting, or pre-grouting, where the boreholes are drilledfrom the tunnel excavation face into the virgin rock in front of the face andthe grout is pumped in and allowed to set, before advancing the tunnelface through the injected and sealed rock volume. Sometimes such pre-excavation grouting can be executed from the ground surface, primarily forshallow tunnels with access to the ground surface area above the tunnel.

• Post-grouting, where the drilling for grout holes and pumping in of thegrout material take place somewhere along the already excavated part ofthe tunnel, because of unacceptable water ingress.

Figure 1.1 Pre-excavation grouting and post-grouting

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The purpose of tunnel grouting in a majority of the cases is ground water in-flowcontrol. Improvement of ground stability may sometimes be the main purpose,but will more often be a valued side effect of grouting for ground water control.Cement based grouts are clearly used more often than any other grout in tunnelinjection, but there are also a number of useful chemical grouts available.

Pressure grouting (injection) into the rock mass surrounding a tunnel, is atechnique that has existed for more than 50 years, and it has developed rapidlyduring the last 15 to 20 years. Much of the development into a high-efficiencyeconomic procedure has taken place in Scandinavia. Pressure injection hasbeen successfully carried out in a range of rock types, from weak sedimentaryrocks to granitic gneisses and has been used against very high hydrostatichead (500 m water head), as well as in shallow urban tunnels.

The effect of carrying out grouting works ranges from close to drip free tunnels(around 1 l/min per 100 m of tunnel, [1.1] and [10.4]), to ground water ingressreduction dictated by practical and economical considerations (like specifiedacceptable remaining ingress in the order of 30 l/min per 100 m, [1.2]). It mustbe emphasised already at this stage that post-injection in this context is only asupplement to pre-injection. This important aspect of tunnel grouting will beexplained later in this Chapter.

1.3 Scope of the book

The scope of this book is pressure grouting around tunnels in rock, excavatedby drill and blast, or by mechanical excavation, using cement based grouts anda range of chemical grouts. Such injection can be required for a number ofdifferent reasons.

The latest technical developments are linked to improvements in materialstechnology and to better equipment and improved practical procedures. Theaim of this book is to present a guide on how to do it, based on the latest stateof the art. To explain why and how things have changed compared to traditionaltechnique, earlier techniques are described to illustrate the advantages of thenew methods. The presented materials technology is primarily based upon MBTUGC International products. This is because of the extreme complexity thatwould result, if different manufacturer’s products were to be covered in parallel.

The book presents practical application techniques of pressure grouting aheadof the tunnel or shaft face and around already excavated tunnel sections. Thepractical focus is supported by theory, when this is found to be appropriate.Practical experience and case studies are therefore extensively used andcomplex theory is deliberately avoided.

When studying available literature about grouting the somewhat arbitrary feelingis that 90% if not more, is dealing with soil grouting, foundation grouting and arange of post-grouting techniques for repair and water ingress control. The veryimportant advantages of pre-grouting, when this is a possible option, has received

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Water Pressure TestingWPT

10 bar

1 Lugeon = 1.0 liter/minuteper meter borehole at 10 bar net pressure

Packer

Packer

very little attention and is almost completely missing in the literature. This bookattempts to fill some of this information gap.

1.4 Traditional cement based grouting technology

Pressure grouting into rock was initially developed primarily for hydro powerdam foundations and partly for general ground stabilisation purposes. For suchworks there is normally few practical constraints on the available working space.As a result grouting was mostly a separate task, and could be carried out withoutaffecting or being affected by other site activities.

The traditional cement injection techniques were therefore applicable withouttoo much of a disadvantage. The characteristic way of execution was:

• Extensive use of Water Pressure Testing (WPT) on short sections ofboreholes (3 - 5 m), for the mapping of rock conditions and waterconductivity (Figure 1.2). This process involves carrying out water pressuretests at regular intervals along the borehole to see what the overall waterloss situation is i.e. which sections of the borehole are watertight and whichsections allow the water to escape. The results were used for decisionmaking regarding cement suspension mix design like water/cement ratio(w/c-ratio by weight), and to choose between using cement or chemicalgrouts.

Figure 1.2 Water pressure testing of borehole

• Use of variable and mostly very high w/c-ratio grouts (up to 4.0) and “groutto refusal” procedures, the latter expression meaning that grout is pumpedinto the rock until the maximum pre-determined pressure is reached andno more goes in.

• Use of Bentonite in the grout, to reduce separation (also called bleeding)and to lubricate delivery lines.

• Use of stage injection (in terms of depth from surface), low injection pressureand split spacing techniques (new holes drilled in the middle betweenprevious holes). One way of stage injection involves drilling to a certaindepth and then injecting the grout and next to re-drill and deepen the samehole and repeating the process. Split spacing as described above is also aform of stage injection.

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Figure 1.3 Relation between rock cover and admissible grouting pressure [1.3](Typical for dams and other foundation grouting)

In conclusion: The traditional cement injection technique, as described aboveand for the reasons given, is rather inefficient when considering the timenecessary and the resources spent in reaching a specified sealing effect. Thisis especially the case when considering working from a tunnel face, where therock cover and limited free surface area allow the use of fairly high pressurewithout the same risk of damage.

1.5 Rationale for the increase in the use of pressure grouting

In the last 20 years, pressure grouting ahead of the face in tunnels (referred toas pre-grouting, or pre-injection), has become an important technique in moderntunnelling works. There are a number of reasons for this:

• Limits on permitted ground water drainage into tunnels are now frequentlyimposed by the local authorities, due to environmental protection and

The typical effect of the above basic approach was that injection operationswere quite time consuming - WPT every 5 m; pumping of a lot of water for agiven quantity of cement; the need for counter pressure (i.e. pumping grout untilthe rock would take no more) causing unnecessary spread of grout; holding ofconstant end pressure over some time (say for 10 minutes) to compact thegrout and squeeze out surplus water; slow strength development and complicatedwork procedures; it all added up to a long execution time. The low maximumpressure normally allowed to avoid any prospect of ‘lifting’ the ground in whichthe grouting was being carried out (typically less than 5 bar, or with a relation torock cover at the packer placement point), reduced the efficiency of the individualgrouting stages leading to more drilling and injection steps, to reach the requiredsealing effect. See Figure 1.3.

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sometimes to avoid settlement above the tunnel. Settlement may causedamage on the surface, e.g. to infrastructure like buildings, roads, drainagepipes, supply lines and cable ducts. See example in Figure 1.4.

Figure 1.4 Northern Puttjern drained by Romeriksporten Tunnel in Oslo (Photo SCANPIX)

• The risk of major water inrushes, or of unexpectedly running into extremelypoor ground, can be virtually eliminated (due to systematic probe drillingahead of the face, being an integral part of the pre-grouting technology). Itshould be noted that if the excavation process hits a major water feature(because it was not detected and not pre-grouted), then water ingress hasto be sealed in a post-grouting situation. This process is not only timeconsuming and expensive, but also far less effective than pre-grouting orpre-injection. In difficult situations, it can be close to impossible to succeed.

• Poor ground ahead of the face can be substantially improved and stabilisedbefore exposing it by excavation. This improves the face area stable stand-up time, thus reducing the risk of uncontrolled collapse in areas of poorground.

• Risk of pollution from tunnels transporting sewage, or other hazardousmaterials, can be avoided or limited. This is because once the ground hasbeen treated by pre-injection it becomes less permeable so such hazardousmaterials cannot freely egress from the tunnel.

• Permanent sprayed concrete tunnel linings are increasingly being installed.The savings potential in construction cost and time is substantial, beingthe main reason for the increased interest in permanent lining shotcretetechnology. Such linings cannot be produced with satisfactory quality underwet (running water) conditions, and ground water ingress control by pre-grouting might become necessary.

With modern tunnelling drill jumbos even very hard rock can be penetrated at arate of 2.5 to 3.0 m/min. In other words, the cost of probe drilling to guardagainst sudden catastrophic water inflows is now low. At the same time it should

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be noted that a large number of projects experience such catastrophic situationsand are often stopped for months. Such events are extremely expensive andtime consuming. It is then quite strange that the low insurance premium oflimited probe drilling is not paid, to avoid the consequences of future possiblehuge water inrushes. This is especially so, when considering that if suchconditions are identified ahead of the tunnel face, they can be treated successfullyat a fraction of the cost and time spent if blasting into it. A list of examples couldbe made long, and some are shown in Table 1.1. (expanded by the authorbased on Fu et al, 2001).

Table 1.1 Some examples of water inrushes at the tunnel face [1.4]

Project Name Length (km) Ingress m3/min GW head (bar) LocationPinglin 12.8 10.8 20 Taiwan, R.O.C

Yung-Chuen 4.4 67.8 35 Taiwan, R.O.C

Central (East Portal) 8 18.6 Taiwan, R.O.C

Seikan 53.8 67.8 Japan

Semmering pilot 10 21 Austria

Gotthard Piora pilot 5.5 24 90 Switzerland

Isafjordur 9 150-180 6-12 Iceland

Abou 4.6 180 22 Japan

Lungchien tailrace .8 81 Taiwan, R.O.C

NorthWest Himalaya 10 72 India

Access Oyestol 5 50 (flow in 1borehole)Norway

Kjela (Bordalsvann) 15 23 Norway

Ulla Forre, Flottene 40 Norway

1.6 Some comments on Post-grouting

Grouting behind the tunnel face (post-grouting), should normally be used intunnelling as a supplement to pre-grouting, to seal off remaining spot leakagesif necessary. This will be especially necessary if the pre-grouting has not producedthe required average tightness within a given section of the tunnel. It is interestingto observe that post-grouting becomes far more effective, when the same areahas already been pre-injected. The normal problem of leakage points shiftingfrom one tunnel location to another, without really sealing them off, is mostlyavoided.

It has been repeatedly experienced in a number of projects that post-groutingalone seldom can produce the targeted result, or only after prohibitive use ofresources. When a certain level of tightness is specified, it cannot beoveremphasised that pre-injection has to be carried out. This is because thisprocess seals the open joints in the rock before the water starts to flow, whereaswith post-grouting the water has started to flow into the tunnel and the joints haveto be blocked with the water flowing through them. One of the problems that has to

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be faced with post-grouting is grout ‘wash-out’. A study summing up some Norwegianprojects indicates that the time and cost of reaching a specified result bypost-grouting, may be 30 to 60 times higher than by pre-grouting [1.5]. A translationfrom Norwegian of the two last sentences of page 3 of this reference reads:

“However, it is recommended in cases where large water inrushes can be expectedand especially at high ground water head, to carry out probe drilling ahead of theface and to carry out pre-grouting if large water flow is detected. Based onexperience the cost of stopping water ingress by post-injection is30 – 60 times higher than that of using pre-injection.”

Other experienced engineers may be using different figures to illustrate theextra cost of using post-grouting exclusively, like 2 –10 times more. An accuratefigure does not exist so the important point to note is the general agreementthat post-grouting is extremely expensive and complicated.

When pumping a grout into rock, the flow of the grout is governed by the principleof least resistance. The shortest flow path inpost-grouting, offering least resistance, is veryoften leading back into the tunnel. To achievespread of grout into the rock volume, backflowhas to be stopped first. Furthermore, if apotential backflow path also carries flowingwater, obviously the injected grout will sufferdilution and wash-out effects. The more water,the higher pressure and the larger the flowchannels are, the more difficult it will be to sealthem off. These are the very reasons for thedramatic cost difference presented in reference[1.5]. See also Figure 1.5.

Figure 1.5 Very difficult to seal by post-injection (Photo: Peter Town)

1.7 New time saving methods and materials technology

The characteristic situation in all modern tunnelling is that the speed of tunneladvance is decisive for the overall economy. This fact is closely linked to thevery high investment in tunnelling equipment, causing high equipment capitalcost. Added to this is the fact that the limited working space at the tunnel facenormally allows only one work operation to take place at a time.

The face advance rate is decided by the number of hours available for actualexcavation works (other factors kept constant). Time spent for pre-injection willnormally have to be deducted from this available excavation time. One hour offace time typically has a value of more than US $1000 and it is evident that theefficient conduct of all activities at the tunnel face is a priority. From this, it canbe seen that injection in a tunnelling environment is fundamentally differentfrom injection for dam foundations and ground treatment from the surface. This

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is the main reason why the technical development in tunnel injection has beendifferent to other types of rock injection.

Because of the need to save time (and therefore cost), technical specificationsfor routine tunnel grouting cannot be loaded with tests and investigativetechniques. If it is required to carry out extensive water pressure testing in stagesin all holes, if core drilling is made part of the routine drilling from the face, ifjoint orientation and crack openings have to be checked by camera etc., and allthis is linked to a complicated system of decision-making during execution ofgrouting, the sum may be termed overkill. Such research related activities cannot be made part of the routine grouting works if cost and efficiency has anypriority. The additional down-side is that such over-zealous procedures willprobably not improve the end result at all.

The last 15 years has led to the development of a number of new cement basedproducts for injection. Typically, these cements are ground much finer and mayoffer more suited setting and hardening characteristics. In most cases, these cementsare combined with admixtures or additives to provide entirely new cement groutproperties and substantially improved penetration into cracks. When combined withworking procedures that are adapted to the new materials properties the efficiencyincrease is substantial. Even though these new cement products are more expensivethan standard Portland cements, they are still very competitive, compared to mosttraditional chemical grouts (refer to Figure 1.6).

180

225 5

00

1300

3335

3335

870

2000

US

$ /

m3

Rap

id

SR

Rh

c650

Rh

c900

PU

R

Wg

l S

Wg

l H

MP

307

Cost of grout ready for injection

Cement grouts: w/c-ratio = 1.0, (gives 1.5 kg/litre)

Polyurethane expansion factor used: 5x

Rapid:

SR:

Rhc650:

Rhc900:

PUR:

Wgl S:

Wgl H:

MP307:

Rapid hardening Portland cement

Sulphate resistant Portland cement

Rheocem 650, micro cement

Rheocem 900, micro cement ultra fine

Polyurethane, water reactive, foaming

Waterglass, soft

Waterglass, hard

Acrylic grout (no acrylamide)

1800

MP

320

MP320: Colloidal silica

Figure 1.6 Relative material volume cost of various injection products

Cement based grouts remain the material of first choice for pressure grouting intunnelling. This is due to the low volume cost, availability, well documentedproperties and experience and environmental acceptability. However, the widerange of available chemical grouts offers a useful supplement to cement grouts,especially when the tightness requirements are strict. Chemical grouts canpenetrate and seal cracks that cementitious grouts will not enter.

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2. GROUTING INTO ROCK

2.1 Particular features of rock (compared to soil)

Rock materials and soils are fundamentally different in terms of the behaviourof water flow and the effect of injecting any kind of grout into the ground.

Soils possess a wide variation in particle sizes, layering, compaction, porosity,permeability and a number of other parameters. However, at basic level soilsconsist of particles and permeability is directly linked to the pores (spaces orvoids) between the particles.

Between discontinuities, most rock materials, on the other hand, are practicallyimpermeable for water and grouts. Leakage and conductivity is therefore linkedexclusively to discontinuities within the rock mass. It is necessary to understandand accept this important difference between soil and rock, to be able to correctlyevaluate all aspects of pressure grouting in rock tunnelling and to understandwhy the approach has to be different to soil injection techniques.

When comparing rock and soil, the similarities and differences are primarilygoverned by how scale is being treated. It is important to understand and takeaccount of the effects of scale to reach correct solutions and answers. If theconditions within a whole mountain are considered, the average “permeability”of the rock mass can be measured and evaluated by the same methods as arenormally used for soils (a similarity). The reason for this is that the overall rockmass fragmentation creates very small block sizes (similar to particles in thesoil case) compared to the whole mountain volume under consideration andthe whole mass can be treated with a reasonable approximation as beinghomogeneous.

In comparison, when considering the rock volume for the first few meters arounda tunnel and along a few meters of its length, single joints and channels willgovern and dominate the pattern of water conductivity and grout take. In such arandomly chosen limited rock volume, the joints and channels can show waterconductivity many orders of magnitude different to the “mountain” averagepermeability (a difference). To use the term permeability in the same sense asfor soils, therefore can be highly misleading. In a perfectly homogeneous sandvolume of a given permeability one could, as an example, calculate 300 l/minwater ingress into a 100 m tunnel length. If mentally assuming that the sand isimpermeable but with an inserted steel pipe through the sand into the sametunnel, the pipe used to feed 300 l/min of water (which could be an illustration ofthe hard rock water conducting channel situation), the average “permeability”would be the same. However, the two situations are certainly totally different inpractical terms if looking for water sealing solutions.

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The permeability term is being used to estimate and illustrate ground waterflow conditions on an overview level also in hard rock (large scale average),which is an acceptable approximation for this situation. However, on a detailedlevel in hard rock, the term permeability is not applicable and practical decisionsmade based on an assumed “permeability” will mostly turn out to be totallywrong.

For injection in soils the following indications have been given by Karol [2.1]:

k = 10-6 or less not groutablek = 10-5 to 10-6 groutable with difficulty by grouts under 5 cP viscosity and

not groutable for higher viscositiesk = 10-3 to 10-5 groutable by low-viscosity grouts but with difficulty when

viscosity is more than 10 cPk = 10-1 to 10-3 groutable with all commonly used chemical groutsk = 10-1 or more groutable by suspended solids grout

Based on the previously mentioned differences between soil and rock, theabove guidelines will not be applicable in most rock materials. With WPT resultsin boreholes as basis for calculation of permeability in rock even section lengthsas short as one meter could easily indicate permeability between one andthree orders of magnitude too low. In addition, the fact that rock injection intunnelling allows the use of much higher injection pressure (often 10 timesmore) will change the practical limits of what is groutable and not.

In a rockmass it is evident that the characteristics of jointing will be of majorimportance for any grouting program. The variation of joint properties and waterconductivity in different types of rock is actually extreme and a discussion ofthis subject is outside the scope of this book.

However, some examples can be given to illustrate the importance of the subjectand to draw the attention to some effects of typical conditions found in rock.Perhaps the most extreme water conductivity situation that can be found is inlimestone, where “carst” features occur. These are solution channels inlimestone formations that can create huge caverns and literally allow asubterranean river. Even when the channel has a typical diameter of only onemeter, the water flow conditions into a tunnel intersecting it would becatastrophic.

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Figure 2.1 Average permeability of soil and rock

Hard rock materials like gneisses, granites and quartzites, will often showunweathered jointing patterns at depth, that may result in a substantial totalleakage potential. Such jointing can be quite easy to inject and seal. Local faultareas, especially major shear zones in the same kind of bedrock, may containa lot of fine material and clay gouge. Such zones will often show no leakage atall due to the fines, but if there are local water bearing channels, they may bedifficult to find and complicated to seal off. Uncontrolled running water in suchchannels may lead to flushing out of fine materials from the zone, resulting inincreasing flow over time. Such effects also depend on the ground water pressure.

Weaker beds like shales, limestones, mudstones, sandstones and somemetamorphic rocks are often jointed and layered to a considerable degree. Ahigh number of water bearing small cracks may in total produce substantialleakage. A complication for a successful injection program in such rock conditions,is often the wide variety of joint filling materials that can be found. Such jointfillings tend to inhibit grout penetration and distribution and the fill materials aresometimes squeezed around by the grout being injected. See Figure 2.1.

Figure 2.2 Effect of conductivity contrast on grout flow into open joints

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In most rockmasses, the main problem for pressure grouting is the non-uniformconditions caused by localised geological features. In a borehole of some meterslength there will, in most cases, be a mixture of joints, cracks and channels,between water-tight sections. Any fluid pumped into such a borehole will inevitablyfollow the path of least resistance. The effect of this is that a given volume ofgrouting material, may follow a very conductive opening at fairly low pressure,to a distance much greater than expected and beyond what is effective. At thesame time, there will be very limited penetration into other openings (due to lowpressure and material “lost” into the main channel). This problem can and veryoften does lead to unsatisfactory grouting results, and/or increased cost, due toincreased number of grouting stages and too high material consumption toachieve the required result. See Figure 2.2 above.

In a rock type with only one clearly dominating joint set, where one would expectwater leakage and grout penetration to generally flow along these joint planes,this is only partly going to occur. Observation of the nature of water ingress inTBM excavated tunnels (where additional blasting cracks are not obscuring thenatural conditions), clearly demonstrates that channels within joint planes arethe typical situation. This is well demonstrated by leakages appearing asconcentrated point ‘jets’ from somewhere along the joint intersection with thetunnel periphery.

Experience from post-grouting in tunnels further supports the idea of channelleakage and channel conductivity as the normal mechanism of watertransmission in jointed hard rock. When a water flow clearly is originating froman identified joint plane, that can be observed crossing the tunnel periphery,drilling can be performed to cut through the joint plane at a suitable depth andangle, with the purpose of getting direct contact to the water flow. Often, anumber of holes need to be drilled across the joint plane, to actually hit thewater leakage. The reason is obvious - most of the joint plane is dry and thewater flows through a limited channel within the plane. When drilling for waterflow contact, it is of course much more difficult to hit a pipe than a plane.

An example can be given from the Norwegian hydro power project Kjela (1977).At tunneling length 1800 m from access Tyrvelid, direction Bordalsvann, thetunnel hit a water inrush of 15’000 l/min. at 23 bar pressure. As could be clearlyseen in the tunnel, more than 90% of this inrush came from one concentratedchannel located within a shear zone.

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2.2 Handling of rock conductivity contrast

Figure 2.3 Large conductivity contrast

For reasons of time-related cost and adequate cover tunnel pre-injection requiresrelatively long boreholes (10 to 30 m) and injection through one packer placementnear the opening. In such length of borehole there will normally be conductivitycontrast along the hole, sometimes this contrast may be extreme. With a largeconductivity contrast and grout flow in direction of least resistance it is necessaryto take steps to reduce the negative effects of this normal situation. See Figure 2.3.

The problem is that chemical grouts will flow into on the large openings at lowpressure doing nothing to seal smaller openings. Cement grouts will have thesame tendency and grout to refusal gives excess material consumption. Stablecement grout and suitable procedures can counteract the problem to a largeextent and increase efficiency. The best way of illustrating how to deal withconductivity contrast is by using an example situation (Figure 2.3), treated withtraditional grout to refusal technique and alternatively with stable cement groutand dual stop criteria.

2.2.1 Description of typical Grout to refusal procedure

Start of grouting with a w/c-ratio 3.0, high grout flow at very low pressure andassuming that 90% of the flow goes in the largest channel. Standard procedureis to reduce the w/c-ratio in steps when the pressure is not increasing. One mayassume that after 3.5 hours spent injecting say 4000 kg of cement and reachingthe maximum allowed pressure (for the specific conditions), the following situationhas been reached:

• cement has travelled in the largest channel to a maximum distance of350 m from the borehole (which is far beyond the useful spread).

Ground surface

Packer

Injection

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• the grout pressure increased gradually, especially during the last part of theinjection time.

• grout permeation into medium and small cracks is only in mm-scale. This iscaused by a long period under low pressure and clogging of the cracks byfilter cake development. Also, when the pressure finally increases the groutused has a low w/c-ratio and higher viscosity and so would not permeatethat easily.

• some of the injected grout has separated, leaving residual openings andconductivity.

2.2.2 Stable grout of micro cement using dual stop criteria

The whole injection can be executed with a fixed 1.0 w/c-ratio and a low viscosityof 32 s Marsh cone flow time, using a thixotropic grout. Also in this case 90%will flow into the largest channel at very low pressure. After one hour of injectiontime the stop criterion of 1500 kg per hole has been reached (pressure still low).(In most practical cases like this the micro cement procedure would utilize alimited volume at w/c-ratio 1.0 like 250 litres, before changing to 0.8 and later to0.6. This will not change the described examples other than in making the microcement alternative work even better). The established situation may be assumedto be as follows:

• micro cement has travelled on the largest channel to a maximum distanceof 125 m from the borehole (which is also beyond the useful spread). Thisshorter distance is primarily caused by less cement being pumped. Seealso next bullet point.

• some penetration has been achieved into medium and small cracks due tothe grout stability, low grout viscosity and smaller particle size

If assuming that the hole length used was 12 m, the next step would be to drilla new neighbour hole with the same length. This would take about 5 to 10minutes with modern drilling equipment. Injection can now be done into thesame area (large channel blocked by first stage injection) and penetration willtherefore be into medium and small cracks at a higher injection pressure. It canbe assumed that it takes 30 minutes to inject 500 kg cement when the allowedmaximum pressure has been reached.

2.2.3 Comparison of the two procedures

Traditional OPC grouting Stable micro-cement grouting

Time spent 3.5 hours 1 hour 40 minutes

Materials spent 4000 kg OPC 2000 kg micro cement

Injected 1 stage, basically one crack 2 stages, large and small cracks

Result ineffective mainly effective

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The micro cement alternative using half the material and less than half theexecution time, has achieved the following result improvements compared tothe OPC procedure:

• Since two grouting stages have been executed, the achieved rock tightnessin the first few meters around the holes is much better. Other reasons forbetter tightness are the fact that the grout viscosity was always very low,the grout was stable (so no re-creation of channels due to bleeding) andthe maximum cement particle size would typically be 1/4th of the OPC.

• The grout durability and strength is substantially better because of thelower w/c-ratio and no use of Bentonite in the mix

It would be an option to also execute two stages using OPC and then the resultcould of course be improved. However, this would then again take additionalgrout and additional time and experience shows that the result would be poorer.The cost of extra cement and even more important, extra time will normallycause substantially higher overall cost for a poorer result, using an OPC andgrout to refusal technique.

2.3 “Design” of grouting in rock tunnels

Design of grouting in rock tunnels means essentially the development andspecification of drilling patterns, the grout materials to be used and the methodsand procedures to be applied during execution. These are the variables whichcan be controlled by engineers, geologists or specialists and which are variedaccording to local actual conditions in the tunnel, with the purpose of achievinga specified result. The outcome cannot be accurately predicted because of thenature of the technique and the lack of details about ground conditions. Nobodycan directly observe what happens in the ground during injection, other thanthe indirect signs and effects on water ingress and by inspection after excavatingthrough the grouted rock volume.

Figure 2.4 Overall situation in km-scale, GW and rock parameters variation in cm-scale

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Even the evaluation of carefully controlled full scale tests can be difficult. Theuncertainty about unforeseen changes in ground conditions from one test locationto the next cannot be accurately quantified. However, most of the principles ofpre-grouting have been developed through and are supported by the results ofseveral thousand tons of grout injection in tunnelling and the understanding ofthe principles is not so much guesswork as it is sometimes claimed to be.

The word “design” probably needs to be commented upon to clarify what itmeans in the context of tunnel grouting. The need for such a clarification arisesfrom the difference to the normal understanding of the term when used instructural design.

Design of a bridge or a high-rise building will include the necessary drawings,materials specifications and structural calculations to define the dimensions,the geometry, the load bearing capacity, the foundations and the general layoutof the object to be built. The whole analysis has to be based on the given physicalsurroundings, the owner’s requirements regarding service loads, service lifeexpectancy and other features or limitations that are applicable.

In the case of a tunnel grouting operation many will expect the above principlesto be applicable so far as the “design” process is concerned. However, the realityis that it is not possible to design the work with precision in advance of it beingcarried out so it is nothing like the “design” process referred to in the previousparagraph. The design of tunnel grouting operations is based upon the bestestimates of the average “permeability” of the rock through which the tunnel isto be driven. The design will usually include calculations of the likely water ingress,drawings showing matters such as the depth, angle and pattern of the intendeddrilling, execution procedures covering all aspects of the operation and thematerials specification, so as to aim at satisfying the required water tightness ofthe tunnel. There is no question of drawings being produced showing what thefinished job will look like or to give accurate dimensions for the result.

The pre-investigations for rock tunnel projects can never give sufficient detailsabout the rock material and the hydrogeological situation for the full length ofthe tunnel, so as to allow a “bridge design” approach. Furthermore, the calculationmethods available are not refined enough to accurately analyse the link betweenthe required result and the necessary steps to produce it. To further compoundthe problem it must also be admitted that even if assuming that a mathematicalmodel would be available there is no chance that all the materials parameterscould be measured, accurately quantified and input to such a model.See Figure 2.4.

The basic design for the grouting operation as referred to above has to beapplied in practice on an empirical, iterative observational design-feedback basis(monitoring of results) as described below:

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• once the “watertightness” requirements are defined, the project data and allavailable information about rock conditions and hydrogeology can be analysedand compared with those requirements. This often includes indicativecalculations of potential ground water ingress under different typical situations.Based on empirical data (previous pre-injection tunnel project experience) acomplete pre-grouting method statement can then be compiled. However,irrespective of how elaborate this method statement (or “design”) is andwhatever tools and calculations are employed to produce it, it will not bemore than a prognosis. This prognosis will express how to execute the pre-grouting (under the expected range of ground conditions), what sequenceof steps to take to meet the required tightness of the excavated tunnel.

• during excavation the resulting tightness in terms of water ingress achievedcan be measured quite accurately. This means that it is possible to moveto a quantitative comparison between targeted water ingress and the actualresult and accurately pinpoint if the situation is satisfactory or not. If theresults are satisfactory, the work will continue without changes, and only acontinued verification by ingress measurements will be necessary.

• If the measured water ingress rate is too high, this information will be usedto decide on how to modify the “design” to ensure satisfactory resultscompared to the requirements for the remaining tunnel excavation. Thismay have to be executed in stages, until satisfactory results are achieved.Excavated tunnel sections which do not meet the requirements of thespecification will have to be locally post-grouted until the overall result forsuch sections are acceptable unless it is possible to compromise on thewater tightness requirements.

2.4 Fluid transport in rock

The permeability of a material expresses how readily a liquid or a gas can betransported through the material. Darcy‘s Law is based on laminar flow, anincompressible liquid with a given viscosity and is valid for a homogenousmaterial [2.2]:

v = k iwhere v = flow velocity

k = coefficient of permeabilityi = hydraulic gradient

The requirement of a homogenous material is never satisfied for jointed rockmaterials, and then only when the volume being considered is big enough.Normally, the term joint permeability, or even better conductivity should be used.

The coefficient of permeability can be measured in the laboratory, using the

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above given formula of Darcy:

q = k A iwhere q = liquid flow rate (m3/s)

k = coefficient of permeability (m/s)A = area of sample across flow path (m2)i = hydraulic gradient

The absolute permeability of a material, for liquids of varying viscosity, can befound according to the following formula:

K = k (�/�) = k (�/g)where K = absolute permeability (m2)

k = coefficient of permeability (m/s)� = dynamic viscosity (mPa s) or cP� = kinematic viscosity (m2/s)g�= 9.81 m/s2

� = volume weight of the liquid (N/m3)

For testing of rock mass conductivity through bore holes, the unit Lugeon is themost frequently used. Lugeon (L) is defined as the volume of water in litres thatcan be injected per minute and meter of borehole at a net over-pressure of 10bar (see Figure 1.2).

The Lugeon value needs interpretation and cannot be considered in isolation. Ifmeasurement has taken place over a bore hole length of say 10 m, then thereis in principle, always the chance that all the water has escaped through asingle leakage location. This means, that if the same borehole had beenmeasured in 0.5 m increments, nineteen of these would have had a L-value ofzero, while one would be 20 times the above measured average.

To avoid possible extreme differences between Lugeon values resulting from asingle measurement over a long bore hole (10 to 30 m) and the real value overshorter segments (like 1 m), technical specifications sometimes requires thatthe Lugeon value calculation length is set to 5 m for all borehole measuringlengths longer than 5 m.

The following table illustrates the different units discussed above:

Materials \ Units Lugeon k (m/s) K (m2)Fine sand 100 10-5 10-12

Jointed granite 0.1 10-8 10-15

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2.5 Practical basis for injection works in tunnelling

Pre-injection in tunnelling may have various purposes and may be carried outunder quite variable geological- and hydrogeological conditions. All these factorswill strongly influence how to execute pre-injection in a given case. However,there are a few basic, practical facts of common nature when at a tunnel facethat must be part of any pre-injection planning and execution.

At a tunnel face, typically there is limited working space and the logistics maybe an added problem. Mostly, working operations at the face are sequential andvery little can be executed in parallel. To keep the cycle time short and the rateof tunnel face advance high, it is extremely important that all work sequencesare as rapid as possible, with as small disturbance and variation as possibleand with a smooth change from one operation to the next. Of course, this isdecisive for the cost of the tunnel, since the time related expenses are runningwhether there is face advance, or not.

One very important aspect of tunnel face injection activity must be emphasised.In general, injection into jointed rock materials is not an easily pre-plannedactivity. Pre-investigations may have yielded a lot of general information, butvery little on a detailed level. On the other hand, a lot of specific and detailedinformation is generated during drilling of holes and during execution of theinjection itself. The temptation on the part of planners and designers to createvery elaborate working procedures, lots of tests, voluminous record keepingand tight supervision is therefore very strong. If such a tendency is not checkedthis can generate very complicated and time consuming decision procedures.Lots of detailed information must be processed with clear lines of authority anddecisions must be made regarding the influence on further future work operations.It is very easy to end up in a situation where the good technical intentions in theend are detrimental to the purpose of the exercise.

Elaborate WPT procedures with the purpose of choosing the type of grout arefrequently relied upon far beyond the technical merit of the procedure. Plottingof experience data to check on the possible correlation between grout take andoriginally measured Lugeon value will be very disappointing. One example ofsuch data is shown in Figure 2.5. All such efforts that the author has comeacross are similar to what is shown in this figure.

Figure 2.5 Correlation between measured L-value and grout consumption [2.3]

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Another basic aspect of pre-injection must be kept as a part of planning andoperation. Regardless of the reason for the pre-injection, as long as it has to dowith water leakage control, 100% water cut off is not realistic or cost effective.Also, when the requirement is expressed as some pre-defined rest leakagelevel in the excavated tunnel, it is not possible to accurately hit the targetedleakage rate (see “Design” of grouting in rock tunnels). Whether applying verystrict requirements (like 2 l/min. and 100 m tunnel), or ten or twenty times this,experience shows a wide result variation around the target value. There is noknown, feasible way of substantially improving this lack of accuracy. There aretherefore clear limitations to what volume of refinements and sophistication thatare reasonable and productive to undertake in the injection procedures.

This may seem negative and may be understood as a complete lack of control ofthe injection process. It is not, because of two main factors:

• Water ingress measurements in already excavated tunnel parts will tell wherethe criteria are not met, how much off the results are, under what conditionsand resulting from which resource allocation already used in probe drillingand pre-injection. The same goes for the tunnel sections with satisfactoryresults. This information and its evaluation can be continuously fed back tothe at-face execution for necessary correction of procedures. Experienceshows that the target results will then be more closely reached and with amore optimal use of resources.

• In those areas where the criteria are not met, post injection can be undertaken,normally starting with the highest-yield leakage points. This technique is veryefficient when pre-injection has already been carried out (otherwise, leakagewould normally just be moved around). Because of the actions described inthe above bullet point, the need for post injection is quickly reduced and thefinal result will meet specified requirements.

Figure 2.6 Double and single cover grouting

Since it is generally so much more efficient to execute pre-injection it is also betterto start out a little on the conservative side with the works procedures and later torelax the approach if appropriate as experience is gained. When requirementsare tight and the potential consequences of not meeting criteria are serious, it willoften be best to simply decide on pre-injection as a routine systematic activityusing a double cover approach (see Figure 2.6). The rationale is that if probe

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drilling in most cases will lead to pre-injection, then this separate activity anddecision-making can be saved thus simplifying the procedures and increasing theefficiency.

In less strict situations e.g. with maximum allowed final water ingress of 30 l/min in100 m tunnel and no consequences in the surroundings of the tunnel, a limitedoverlap of typically 5 m per 20 m probing length (25%) can be used. In this type ofcase normally probe drilling will be used to provide basis for decision about whereto actually execute pre-injection. Sections of the tunnel that are relatively drywithout injection will then be passed through using probing alone. Where injectionhas to be done this can be the so-called single cover approach, see Figure 2.6.

2.6 Grout quantity prognosis

Practically all pre-grouting in hard rock tunnelling is based on the use of cement(OPC or micro-cement). In special cases, like in ground conditions with clayand other fine materials on the jointing planes and/or when the required tightnesscannot be reached with cement only, chemical grouts may become necessaryas a supplement. There is no experience basis available for the use ofpredominantly chemical grout, to illustrate typical consumption. However, in thecase of cement injection this can be done.

Also in the case of cement only grouting, the required quantity will depend on alarge number of factors and any estimate made in advance will be inaccurate.The main influence factor is the rock conditions (properties of the jointing),where a limited number of large open channels will tend to require more cementthan cm-scale joint spacing producing frequent drips (distributed “rain” in thetunnel). Other important factors are required tightness, static head of groundwater, tunnel cross section and even the type of cement and injectionmethodology applied.

From sub-sea tunnelling with systematic probe drilling and partly with systematicpre-grouting there are average consumption values from quite variableScandinavian conditions between less than 20 kg/m tunnel to more than 250kg/m. As an extreme case the Bjoroy sub-sea road tunnel stands out with asection of about 500 m tunnel length consuming 2000 kg/m. Target water ingresslevel was typically 30 l/min per 100 m tunnel.

When evaluating empirical data covering such a wide range it can be useful toview the data on a probability basis. Three different figures can be used toillustrate the experience data available from Norwegian sub-sea road tunneling:

1. Minimum average consumption, with 5% probability that the average willbe lower than this figure

2. The probable average consumption

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3. Maximum average consumption, with 5% probability that the average will behigher than this figure

The minimum can be expressed as 15 kg/m tunnel, probable value is 50 kg/m andthe maximum average is 500 kg/m. These values are roughly representative ofpredominantly hard rock types (but not only granitic rock materials) and the tunnellength would have to be 1000 m or more to yield a reasonable average. Obviously,such figures can only be taken as an illustration of what has been experiencedbefore and they can not be transferred directly and accurately to new projects inother ground conditions.

It must be mentioned for clarity that the figures are averages including tunnelsections that needed no grouting at all.

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3. FUNCTIONAL REQUIREMENTS

3.1 Influence of tunnelling on the surroundings

Any tunnel excavated will influence the immediate surroundings to some extent.Depending on the location of the tunnel and its design and purpose, groundconditions, hydrogeological conditions etc., such influence could cause problems.

The main issues that need evaluation can be listed as follows:

• Purpose of the tunnel and the requirements of lining design (drained orwater tight). Most linings are drained, even if there is a horse-shoe umbrellainstalled to prevent water from dripping on the road or on installations inunder ground facilities. See Figure 3.1. To produce actually water tight tunnellinings is very complicated and costly, especially if the ground water headis high.

Figure 3.1 Typical water proofing, drained solution

• Location of the tunnel, especially in relation to other infrastructure, otherexcavations, lakes, rivers and ground water level. Most tunnels are belowthe local ground water level.

• Rock and soil cover, type of tunnelling ground, water conductivity of theground.

• Possible consequences of in- and out leakages on economy, environment,safety and health. Out-leakage can be as much of a problem as the otherway around. Hydro power pressure conduits will loose water and electricityproduction and sewage may cause pollution.

• Requirements and limitations for the construction phase as well as for thepermanent use of the tunnel, which may be different.

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Tunnel drainage effect

Very small water ingress to the tunnel =>several meter pressure drop in the sand =>pore pressure loss and settlement in the clay

The possible consequences of tunnel excavation on the surroundings, may belisted as follows:

• Ground water ingress may cause settlement of soil deposits above thetunnel. This is typically a problem where clay deposits loose their porepressure. With buildings and other structures founded on clay, severedamage may arise. Such problems may occur already at ingress levels of1 to 5 l/min. per 100 m tunnel. See Figure 3.2.

Figure 3.2 Particularly sensitive situation. Examples of several dm settlement

• Lowering of the general ground water level can have a number of effects.Ingress of oxygen to wood foundations will cause rotting. Some rocks, likealum shale may swell due to the creation of gypsum, causing damage tofoundations and other structures. Earth pressure on sewage lines, cableducts etc., will increase.

• Ground water resources like springs and wells may be influenced, or lost,vegetation may dry out and farming activities may be damaged. What canbe accepted, depends very much on climatic conditions and relationbetween surface run-off and remaining water quantity actually going intothe ground.

• Out-leakage consequences will very much depend on what liquid andcomponents in the liquid that is leaking out and the hydrostatic head. Watermay cause splitting, jacking or washing out effects at high head and waterinflux at unwanted locations also at lower head. Contaminated water likesewage, hydrocarbon liquids, poisonous liquids, gases etc., will in mostcases cause severe environmental problems in the surroundings.

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3.2 Conditions inside the tunnel

Inside the tunnel, water ingress will also have consequences. Theseconsequences are different in the construction phase, compared to during theoperation:

• In the tunnel construction phase, the problems are primarily of a practicalnature. When excavating on a decline, water runs to the face and has to bepumped out. The acceptable quantities are smaller for a TBM excavation(where less than 0.5 m3/min. at the face, will cause problems), than for drilland blast (D&B) (where 2.0 to 2.5 m3/min may be handled reasonablyeasily) and will also depend on a number of other factors. Tunnels actuallybeing driven on an incline, but with access through a shaft or a decline, willrequire constant pumping. Naturally, pumping of water may become animportant cost factor, at high volumes or high pumping head.

• Water ingress can behave in quite a number of different ways. Concentratedhigh volume and high pressure in-rush, may cause flooding and severeproblems and time loss (refer to the example mentioned in Chapter 2,Kjela). Also distributed water ingress and generally wet conditions will causeproblems, like poor conditions for shotcrete application, concrete works,construction road works, construction phase dewatering and drainage,unstable railway etc. Water may have a high or a low temperature, causinga very poor working environment and it may contain salt. Salt waterproduces corrosion and problems with all electric equipment underground.

• Depending on rock type and quality, water can create instability, rockdecomposition, rock swelling and washing out.

• In the permanent use of the tunnel, wet conditions will produce similarproblems as mentioned above. Typically, during the operation phase tunnelswill have technical installations of different kind, like the permanentventilation system, electricity supply and operation systems in metro tunnels.Humid conditions will over time cause corrosion, electric failures and thelike. The maintenance and repair cost may become high.

• In cold climate and ventilated tunnels, water ingress can cause ice build-up. In most cases this cannot be permitted and has to be taken care of if itoccurs. In a traffic tunnel, even local minor drips (less than 1 l/min. per 100m tunnel) of minor or no concern above the freezing point, can turn intoserious problems when the frost volume is high enough.

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3.2.1 Calculation of water ingress to tunnels and tightness of grouted zone

Parameter list:

q ground water ingress flow rate m3/s per m of tunnelhs thickness of soil above the tunnel mhw height of water mhr thickness of rock above the tunnel mr tunnel radius mk coefficient of permeability m/s

Figure 3.3 shows an example situation with the parameters necessary for thecalculation of ground water flow rate into a tunnel, including the formula to beused.

The physical significance of the parameters will depend on the actual situation.It is important to note that hr and k represent the thickness of ground where themain part of the potential-reduction takes place (energy dissipation or pressureloss).

Figure 3.3 Ground water ingress formula

When the soil permeability is much higher than in rock, then hw in the aboveformula must be replaced by (hw + hs). On the other hand, if the soil is at least astight as the rock, then hr must be replaced by (hr + hs).

When injection has been carried out around the tunnel and the injected zone issubstantially less permeable than the surrounding rock mass, then hr has to beexpressed as the sum of the tunnel radius r and the thickness of the injectedzone, while hw will be replaced by the sum of hw + hs+ thickness of not injectedrock mass. See [3.1].

A typical situation for an urban tunnel at shallow depth:

In critical bedrock low points, filled with sand and marine clay and with buildingson top, a set of assumed example dimensions are shown in figure 3.4.

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Figure 3.4 Shallow tunnel with soil and rock cover

If the average rock mass permeability in Figure 3.4 is k = 10-7 m/s, this wouldgive a water ingress rate of 24.2 l/min per 100 m tunnel (using the above formula).

A typical tightness requirement for such a tunnel to avoid settlement andsurface damage could be 5 l/min per 100 m of tunnel, which corresponds toq = 8.33•10-7 m3/s and m. With the dimensions shown in Figure 3.4 and anassumed injected zone thickness of 15 m the required permeability of theinjected rock would be:

hr = 1.75 + 15 = 16.75 mhw = 10 + 5 = 15 m

and input in the formula:k = 1.23•10-8 m/s

To achieve a reduction of the water ingress rate to about 1/5th the grouted zonepermeability must be reduced to about 1/8th.

A typical deep situated tunnel:

Figure 3.5 Deep situated sub-sea tunnel with soil and bedrock cover

The assumed dimensions are shown in Figure 3.5. If we assume that the injectedzone has the same thickness of 15 m as in the shallow case and that the resultingpermeability after injection is also the same, then the increased hydrostatichead under the shown geometry would produce a ground water ingress of:

hr = 1.75 + 15 = 16.75 mhw = 30 + 85 = 115 m

and input in the formula:q = 3.44•10-6 m3/s and m = 20.6 l/min per 100 m

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3.3 Special cases

In hydro power tunnel construction, water transfer tunnels are often constructedas drained structures. Even pressure tunnels and pressure shafts may bedesigned as drained (unlined) conveyors when the rock conditions and the rockstresses allow such a solution. Naturally, there will be local areas where injectionhas to be carried out, to limit the loss of pressurised water and thereby electricityproduction.

In pressurised unlined water conduits (where the rock has to sustain the waterpressure) there is one pre-requisite to be aware of. The minimum principal rockstress must be larger than the water pressure in all locations otherwise thewater will find its way out on cracks and joints in the rock mass and hydraulicfracturing is very likely to occur. In such a situation, normally leading to substantialloss of water, the option of grouting as a method of repair is ruled out. Thegrouting may temporarily help reducing the flow, but the risk of another fracturingsomewhere along the tunnel (or shaft) is quite high.

Figure 3.6 Typical layout of a sub sea road tunnel. Probe drilling and some grouting is normal

Special situations can be found around the start of a steel lined undergroundpenstock and around concrete plugs for the sealing off of an adit to a pressuretunnel. Desilting chambers experience frequent water head changes, whenswitching between operation and emptying for sediment removal. Parallelchambers may be located quite close to each other and the pressure gradientfrom a chamber in use to one that is empty can be very high.

Even more of a special nature are compressed air surge chambers underground,gas and oil storage caverns underground and caverns for public utilities, civildefence and storage of goods.

Sub-sea tunnels are special in at least two respects: 1.-The salt water ingressand 2.-The water reservoir above the tunnel is unlimited. See Figure 3.6.

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3.4 Requirements and ground water control during construction phase

Based on the above evaluations on the functional requirements for the tunnel,the tunnel design and execution and its relation to the surroundings; a numberof issues have to be decided regarding the ground water control program. Thedifficult problem to solve is how to satisfy the requirements during all stages ofconstruction and operation of the tunnel.

One requirement that is frequently overlooked, is the water ingress rate duringthe construction phase of a project. If the tunnel will be constructed in an urbanarea and ground water lowering could cause settlement damage to infrastructureon surface, then it is not enough to plan for a final water tight permanent stagelining. It may take weeks and months between the time of exposing the groundat the face, until the water tight lining has been established in the same location.Meanwhile, substantial volumes of water may have entered the tunnel, loweringthe ground water level. Frequently it is too late to prevent settlement and damage,if the ground water level comes up to normal again some months later. Thesituation illustrated in Figure 3.2 is such a case.

The only available tunnelling technique that can keep the ground water in-leakagenear zero, is the Earth Pressure Balance Machine (EPBM), full face mechanicalexcavation using a pressurised shield and gasketed concrete segmentinstallation. Such machines are for soil excavation and are limited to shallowdepths (typically less than 15 meters).

In hard rock tunnelling this alternative is not available, even if a TBM and concretesegments are used for the excavation and support. Without pre-injection theleakage volume could locally become far too large, between the time of exposureand the time of segment erection and efficient annular space backfilling. With aserious local water inrush at hand, such segment handling and grouting wouldalso be very difficult.

Ordinary in-situ concrete lining, even with waterstop in the construction joints,has hardly any influence on the water ingress level, as shown by ingress levelsof 10 to 40 l/min per 100 m tunnel. [3.2]. In the Oslo area this is typically the ingressrate for an unlined and not pre-injected tunnel. Concrete lining with careful highpressure grouting of the interface to the rock was still quite successful. Concretelining with PVC membrane gave acceptable result, but was also not completelywater tight. [3.2]. Two important conclusions can be drawn:

1. A concrete lining will frequently be in place too late to prevent permanentdamage on surface

2. Concrete lining with contact grouting or PVC membrane will typically costmore than an extensive pre-grouting operation, achieving about the samefinal result

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Therefore, there are situations where probe drilling and pre-grouting has to beexecuted to meet the requirements of ground water control during theconstruction phase.

3.5 Measurement of water ingress to the tunnel

As described under “Design” of grouting in rock tunnels, there is no way ofdirectly and accurately linking the grouting works effort and the final water ingressresult. The result has to be monitored, corrected if necessary by doing post-injection as needed and by correcting the way the pre-grouting is being executed.

To be able to accurately determine what is the water ingress result after injection,this has to be measured for pre-defined tunnel lengths. Depending on therequirements and the necessary accuracy of these measurements, tunnellengths could be 10 m, 100 m or even more. The normal way of measurement isby dams in the tunnel floor (especially prepared and sealed to avoid wrongresults) equipped with an overflow V-notch (or any other defined shape that canbe used to calculate the flow rate).

One alternative is the 90° V-notch where the height of water above the bottomof the notch can be used in the formula:

q = 43 • 10-6 • h2.5

where q is flow of water in l/s, h is the water height in mm above the bottom ofthe V-notch. For quick reference, the diagram in Figure 3.7 can be used.

Figure 3.7 Measuring water flow rate by V-notch overflow

0.20.1 0.4 0.6 0.8 1.0 2.0 4.0 8.06.0 10 20 40 60 80 100

100

200

300

Log scale: q in l/s

Hei

ght:

h in

mm

90

h

q = 43 x 10 x h-6 2.5

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4. CEMENT BASED GROUTS

4.1 Basic properties of cement grouts

4.1.1 Cement particle size, fineness

Any type of cement may be used for injection purposes, but coarse cementswith relatively large particle size, can only be used to fill bigger openings. Twoimportant parameters governing the permeation capability of cement, are theparticle size and particle size distribution. The average particle size can beexpressed as the specific surface of all cement particles in a given quantity. Thefiner the grinding, the higher is the specific surface, or Blaine value (m2/kg).For a given Blaine value, the particle size distribution may vary and the importantfactor is the maximum particle size, or as often expressed the d95. The d95

gives the sieve dimension where 95% of the cement particles will pass through(and conversely, the remaining 5% of the particle population is larger than thisdimension. The maximum particle size should be small, to avoid prematureblockage of fine openings, caused by jamming of the coarsest particles andfilter creation in narrow spots.

The typical cement types available from most manufacturers, without asking forspecial cement qualities are shown in Table 4.1.

Table 4.1 Fineness of normal cement types (largest particle size 40 to 150 µm)

Cement type \ Specific surface Blaine (m2/kg)Low heat cement for massive structures 250Standard Portland cement (CEM 42.5) 300-350Rapid hardening Portland cement (CEM 52.5) 400-450Extra fine rapid hardening cement (limited availability) 550

The cements with the highest Blaine value will normally be the most expensive,due to more fine grinding.

Table 4.2 gives an example of particle size distribution of cements commonlyused for pressure injection. Please note that the actual figures are onlyindications, since the table is based on single measurements, from single cementsamples.

40

From an injection viewpoint, these cements will have the following basicproperties:

• A highly ground cement with small particle size, will bind more water than acoarse cement. The risk of bleeding (water separation) in a suspensioncreated from a fine cement is therefore lower and a filled opening willremain more completely filled.

• The finer cements have a quicker hydration and a higher final strength.This is normally an advantage, but causes also the disadvantage of shorteropen time in the equipment. High temperatures will increase the potentialproblems of clogging of lines and valves. The intensive mixing required forfine cements, must be closely controlled, to avoid heat development causedby the friction in the high shear mixer, and hence even quicker setting.

Table 4.2. Particle size of some frequently used injection cements

Percent passing�m Norwegian Spinor A12 W650 Blue Swedish

rapid Ciments Circle Injectionhardening cement

(RP38) d’Origny Degerhamn1 7.0 12.9 10.1 12.63 22.0 59.0 31.2 30.45 32.0 82.5 45.2 40.510 50.7 98.3 68.8 55.415 65.6 100.0 86.5 66.620 76.9 95.5 73.825 86.3 99.1 80.932 95.6 100.0 90.440 99.6 97.150 100.0 99.8

���������������m90%< 27,3 6.4 16.6 31.610%< 1.3 0.5 1.0 0.9Averageparticlesize 9.8 2.5 5.9 7.9

The finer cements will give better penetration into fine cracks and openings.

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This advantage will only be realized as long as the mixing process is efficientenough to separate the individual particles and properly wet them. In a purecement and water suspension, there is a tendency of particle flocculation aftermixing, especially with finer cements, and this is counter-productive. It is commonlysaid that the finest crack injectable, is about 3x the maximum particle size (includingthe size of flocculates). For standard cements, this means openings down toabout 0.30 mm, while the finest micro cements may enter openings of 0.06 mm.

The question is sometimes raised, what is the definition of microcement.Unfortunately, this question cannot be answered based on any kind ofinternationally accepted agreed definition and it is left to common practice andcase by case identification. As an informative indication of a minimumrequirement to apply the term micro cement, the following suggestion can beused:

Cement with a Blaine value > 600 m2/kg and minimum 99% having particle size <40 µm.

The above “definition” fits quite well with the International Society for RockMechanics reference [4.1]:

“Superfine cement is made of the same materials as ordinary cement. It ischaracterised by a greater fineness (d95 < 16 µm) and an even, steep particle sizedistribution.”

An example of a micro cement just satisfying the superfine “definition” can befound in Chapter MBT Injection Materials. The Rheocem© 650 has a Blaine valueof 650 m2/kg and the particle distribution shows 94% < 15 mm.

The effect of water reducing admixture (or dispersing admixture) when mixing amicro cement suspension can be seen in Figure 4.1 [4.2]. It is quite evident thatthe reduction of d85 by the use of a dispersing admixture from about 9 µm to5 µm will strongly influence the penetration of the suspension into the ground.If these figures are put into the soil injection criteria of Mitchell [4.3], a goodinjection result with this cement without admixture could be achieved in a soil withd15 > 0.22 mm. With admixture the same result could be obtained in a soil withd15 > 0.12 mm. Also in rock injection the effect would be significant.

42

Another important effect of water reducing admixtures is the lowered viscosity ata fixed w/c-ratio. The effect of lower water content is improved final strength ofthe grout, but more important is lower permeability and better chemical stability.The compressive strength of a pure water and cement mix using a standard OPCis about 90 MPa at w/c-ratio of 0.3 (which will be far too stiff to be used for normalinjection). Already at a w/c-ratio of 0.6 the strength will drop to 35 MPa and whenusing grout mixes with w/c-ratio above 1.0 the strength is finally in the range of 1.0MPa and less. (Rheocem® 650 microcement with 1.5% admixture reaches 10MPa compressive strength after 28 days). More important in cases with evenhigher water content is that the permeability is pretty high and the strength is solow that if any water flow takes place, it can lead to mechanical erosion andchemical leaching out of hydroxides (hydration products from cement reactingwith water).

Figure 4.1 Dispersing effect of an admixture when using micro-cement [4.2]

43

4.1.2 Bentonite

Bentonite has traditionally been used on a routine basis in combination withcement for grouting of soil and rock. The reason to do so was the strong tendencyof standard cement to separate when suspended in water, enhanced by thenormal use of water cement ratio > 1.0. Bentonite can be used to reduce thebleeding in such grouts and a standard dosage of 3 to 5% of the cement weighthas a strong stabilising effect.

Bentonite is a natural clay from volcanic ashes and the main mineral ismontmorillonite. There are two main types:

• Sodium-bentonite (Na-)

• Calcium-bentonite (Ca-)

Mostly the sodium-Bentonite is used as an additive in cement grouts, becauseit swells to between 10 and 25 times the original dry volume when mixed inwater. The particles resemble the shape of playing cards and will adsorb wateron the particle surfaces, thus stabilising the grout mix. The particles also sinkvery slowly within the suspension because of the shape. See Figure 4.2.

Fig 4.2 Idealised structure of Bentonite clay after dispersion in water.

With the traditional cement grouting methods and materials Bentonite had itsplace. However, in combination with micro-cements it is normally not necessaryand will mostly be of disadvantage. One reason is that a typical d95 particle size ofBentonite clay is around 60 µm. This is two to three times larger than what isfound in good micro-cements and will reduce the penetration achievable by agiven cement. The shape of the particles are also a negative property in thisrespect. Modern micro-cement grouts can be made with very low viscosity andlimited or no bleeding if combined with chemical admixtures and the Bentonite useis therefore unnecessary and negative for the result.

The final strength of the grout is not important in most cases. However, at highground water head, or when a ground stabilisation effect is valuable, the use ofBentonite at normal dosage will reduce the grout strength by 50% and more.This is avoided when using modern admixtures in micro-cement grouts, withoutsacrificing stability or penetration.

44

4.1.3 Rheological behaviour of cement grouts

Cement mixed in water as an unstable suspension, or as a stable paste (in termsof water separation), behaves according to Bingham‘s Law. Water and trueliquids have flow behaviour according to Newton‘s Law. These laws are as follows:See Figure 4.3

Bingham‘s Law: � = c + � dv/dxNewton‘s Law: � = � dv/dxwhere: ��= flow shear resistance (Pa)

� = viscosity (Pa s)dv/dx = shear velocity (s-1)c = cohesion (Pa)

Figure 4.3 Rheological behaviour of Newton and Bingham fluids

When a stable grout has a very low w/c-ratio, or when ground mineral powder orfine sand has been added, the grout may also have an internal friction.To cover this property, Lombardi has proposed the following rheologicalformula [4.4]:

� = c + � dv/dx + p tan�where: p = internal pressure within the grout

� = angle of internal friction of the grout

A true liquid will flow as soon as there is a force creating a shear stress. Waterin a pipe will start flowing, as soon as there is an inclination. A liquid with ahigher viscosity than water will also flow, but at a lower velocity.

A cement suspension or paste, will demonstrate some cohesion. The differenceto liquids is that the cohesion has to be overcome, for any flow to be initiated. Ifthe internal friction is negligible, the paste will thereafter behave in a similarmanner as a liquid. The rheological parameters of cement suspensions can be

45

influenced by w/c-ratio, by chemical admixtures, by bentonite clay and by othermineral fillers. As an example, it is possible and often useful, to create a groutwith a high degree of thixotropy. This means a paste with a low total flowresistance while being stirred or pumped, but shortly after being left undisturbed,it shows a very high cohesion.

4.1.4 Pressure stability of cement grouts

For the purpose of controlling grout flow in the ground (to be able to place thegrout where it is wanted), the control of the rheological parameters of the groutis vital. In this context, there is one more factor that is very important: The groutstability under pressure, which is not tested or reflected by the normal check onbleeding. The best way to illustrate the point, is to consider two different grouts,both having w/c-ratio low enough for zero bleeding. If these grouts are filled intoa container with a 45 µm micro filter in the bottom and subjected to pressure, twothings may happen:

• The grout with a good stability, will loose a very small quantity of waterthrough the filter and the thickness of dried out and compacted grout ontop of the filter will be very thin. The main part of the grout under pressureremains uninfluenced.

• A grout with a poor stability will over the same time loose much more waterthrough the filter and a thick layer of dried out and compacted grout will befound on top of the filter. If the pressure is high enough and the grout stabilityis very poor, all the grout volume may be dried out and compacted.

The standard method for testing the pressure filtration coefficient (Kpf) is theAmerican Petroleum Institute (API) Recommended Practice 13. The coefficientis defined as the volume of water lost using the API filter press divided by theinitial volume, divided by the square root of the filtration time in minutes, using a6.9 bar pressure (100 psi).

When squeezing out a small quantity of water from the grout at the injectionfront (which is well simulated by the API pressure filtration test), internal frictionwill quickly increase the flow resistance enough to stop further permeation. Thiswill cause the pump pressure to increase, having the effect of more water beingpressed out and a rapid development of a plug. This will happen more readilywith a poor stability grout and often in positions where the openings are muchbigger than the rule of thumb 3x maximum particle size.

Practical project experience and results support the above views and it is likelythat the grout stability is much more important for the permeation of a cementgrout, than some limited difference in particle size.

46

4.1.5 Use of high injection pressure

High injection pressure has proven very successful in achieving low water ingresslevels, far better than what was within reach some years ago. As describedabove the pressure filtration is an important factor in this and it is clear that thebest effect will be reached with a combination of a high grouting pressure (above50 bar) and a grout with a low filtration coefficient.

Furthermore, the grouting pressure, when high enough, will also dilate the cracksand joints of the rock formation and thus increase penetration by increasing theopening size. If high pressure is used without careful consideration of theconsequences, it will be possible to cause damage. Especially, be careful not touse very high pressure in combination with large grout quantities in a singlecontinuous pumping sequence.

Keil et al [4.5] used stable microfine cement injected into a granite formation.This full scale injection test was well instrumented and revealed opening andclosure of fracture zones by as much as 100 micron. Analysis of specimensfrom the grouted formation revealed penetration into cracks as fine as 20 micron.It should be noted that the grout used had a relatively high viscosity of 44 secondsMarsh cone time.

4.1.6 Grout setting characteristics

Ordinary Portland cements will typically show the following ranges of initial andfinal setting times and 24 hours uniaxial compressive strength (ISO mortar,MPa):

Initial set: 140 to 240 minutesFinal set: 190 to 240 minutes (10 to 20 MPa at 24h)

A typical high early strength (rapid hardening) Portland cement in comparison:

Initial set: 80 to 180 minutesFinal set: 150 to 240 minutes (15 to 30 MPa at 24h)

From a practical point of view, initial setting time cannot be made much shorter,without potential problems of build up in equipment and clogging of materiallines. Of course, it is possible to use admixtures to control the open time, whichis covered separately.

One has to be aware that final set has limited relevance compared to strength,or hardening created by cement hydration. Under field conditions in tunnelinjection, the ground water hydrostatic pressure may be in the range of 10 to 50bar (sometimes even higher). If a high hydrostatic pressure is combined withfairly large openings, then sufficient time has to be allowed at the end of an

47

injection stage, before any drilling or blasting into the same area. Otherwise, apuncture may occur and injected cement and water is flushed back into thetunnel, thus destroying the work carried out and creating a hazardous condition.The necessary time will also depend upon the w/c-ratio of the injected groutand at w/c-ratios substantially greater than 1.0, whether or not compaction hasbeen carried out by standing end pressure.

In extreme cases, the necessary waiting time may be as long as 24 hours(above 30 bar and openings larger than 50 mm). In a more moderate case(pressure of 5 to 25 bar and maximum openings up to 25 mm), a waiting time inthe range of 10 to 15 hours should be sufficient. As a rule of thumb, keep inmind that the compressive strength reached at a w/c-ratio of 1.0 will be only 25to 30% of that at w/c-ratio of 0.4 and a further reduction to only 5% at w/c-ratioof 2.0. From this, it should be quite obvious that it will pay off to carefully evaluatethe situation under difficult conditions and control the w/c-ratio.

4.2 Durability of cement injection in rock

There is a large volume of hard rock tunnelling with extensive use of pre-injectionas part of the tunnel design and as the sole measure of permanent groundwater control. The primary experience basis is probably in Scandinavia, whereNorway alone has close to 100 km of sub-sea tunnelling. Even though some ofthese tunnels go down to as much as 260 m below sea level and the groutinjection works carried out are of a permanent nature, there is no report indicatingthat grout has degraded.

The Norwegian Public Roads Administration operates 17 sub-sea tunnels ofvarious different ages (the oldest tunnel goes to Vardø island and wascommissioned in 1981) excavated through quite variable ground conditions. Infact, the general trend reported is a slow reduction of water ingress over theyears as opposed to any sort of degradation in the grout which, of course, if itoccurred would lead to an increase as opposed to a reduction in the wateringress. Melby [4.5] presents a paper dealing with 17 different projects totalling58.6 km of tunnelling. A comparison of water ingress at the time of opening andmeasurements made in 1996 shows the average ingress in 1996 to be only62.9% of the ingress recorded when the tunnels opened. None of the tunnelsshowed an increase in the leakage rate.

The Norwegian national oil company Statoil constructed three pipeline sub-seatunnels amounting to a total of 12 km, going down to 180 m below sea level. Thetunnels are crossing Karmsundet, Førdesfjord and Førlandsfjord. During morethan 15 years of operation Statoil has recorded the energy-consumptionexpended in pumping of ingress water from the deepest point in the tunnels tosea level discharge. Statoil states that there has been no increase in groundwater ingress, since the energy consumed has not increased [4.7].

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Very important for the quality and durability of cement grouts is the w/c-ratio andwhether the grout is stable or segregating. Modern grouting technology in tunnellingmeans stable grouts and thus also w/c-ratio below a certain limit, depending onthe type of cement and the admixture used. This view is supported by the ISRM,Commission on Rock Grouting, Final Report, which states in Chapter 4.2.6 [4.1]:

“Stable or almost stable suspensions contain far less excess water than unstableones. Hence, grouts with a low water content offer the following advantages:

- During grouting:

• higher density, hence better removal of joint water and less mixing at thegrouting front

• almost complete filling of joints, including branches

• the reach and the volume of grout can be closely delineated

• grouting time is shortened because little excess water has to be expelled

• the risk is reduced that expelled water will damage the partially set grout

- After hardening:

• greater strength

• lower permeability

• better adhesion to joint walls

• better durability

4.3 Accelerators for cement injection

It is frequently claimed that there is no need for relatively fast setting cement forrock injection, because it is possible to use an accelerator in combination withslow cements, when needed. This is partly correct, but when considering theuse of microfine cement in combination with quick setting to speed up tunnelling,then the picture is different.

The main point is that accelerators will cause flocculation of the cement particleswhen added to the grout. In the case of a microcement, this is defeating thepurpose of paying for and using a microfine cement. Furthermore, in most casespart of the injection will be carried out without accelerator and the accelerator isadded for special local purposes. The downside of this is that at the end ofinjection, there will be some grout setting fast, but most of the volume is slowand this volume will be dimensioning for the waiting time.

49

SA 160

Rheocem

The MBT range of specially adapted micro-cements for tunneling are namedRheocem©. These cements are fast setting without any added accelerator, thusovercoming the above described problem.

Even when using a quick setting Rheocem© grout there are situations whereacceleration can be necessary. This will typically be in post-grouting to cut offbackflow, but this problem sometimes also appears as backflow through theface in pre-injection. If for any other reason the grout is pumped into runningwater, or pressure or channel sizes are extreme, accelerated grout may becomenecessary.

The best option in combination with Rheocem© is MEYCO® SA 160 accelerator(MBT alkali free accelerator for sprayed concrete). This product seems to createno flocculation before the setting is initiated and then it sets pretty fast. Thestandard MEYCO® SA 160 product can be diluted up to 50% by adding water,before addition to the grout. The practical way of using SA 160 is described inChapter 9.

Normal dosage (calculated on un-diluted MEYCO® SA 160) will be in the rangeof 0.1 to about 3% by weight of cement. Low dosages can be added to the groutin the mixer (but it is NOT recommended), while higher dosages must comethrough a separate hose to the packer head.

The non-return valve that is needed for use with a dosage pump for MEYCO®

SA 160 through a separate hose to the packer head is shown in Figure 4.4.

Figure 4.4 Non-return valve for accelerator dosage (dimensions in mm)

Practical experience has shown that this system works very well and can competewith other alternatives (like quick-foaming polyurethane) to block backflow, mostlyeven without loosing the borehole for further injection without accelerator.

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5. CHEMICAL GROUTS

Chemical grouts consist of only liquid components, which leads to a quite differentbehaviour than cementitious grouts. Chemical grouts behave like Newtonianfluids, demonstrating viscosity but no cohesion (see Figure 4.3). Therefore thepenetration distance from a borehole and the placement time for a given volume,only depend on the viscosity of the liquid grout and the injection pressure used.Chemical grouts available include silicates, phenolic resins, lignosulphonates,acrylamide and acrylates, sodium carbomethylcellulose, amino resins, epoxy,polyurethane and some other exotic materials.

For practical purposes there are two main groups of chemical grouts available:

• Reactive plastic resins

• Water-rich gels

The reactive resins may be monomers or polymers that are mixed to create areaction (polymerisation) to a stable three-dimensional polymeric end product.When short reaction times are used, normally such products are injected astwo-component materials, mixing taking place at the injection packer upon entryinto the ground. At longer reaction times even two component materials can beinjected by a one component pump. Mixed batches only have to be small enoughand with long enough open time to be injected before the polymerisation reactiontakes place. Such products will not be dissolved in water, but they may reactwith water. For proper reaction and quality of the end product the rightproportioning of the components is important. Two component pumps mustfunction properly for this to be satisfied.

The gel forming products are dissolved in water in low concentrations and theliquid components therefore show a very low viscosity (often almost as fluid aswater). When the polymerisation takes place, an open three dimensionalmolecular grid is created, which binds a lot of water in the gel. The water is notchemically linked to the polymeric grid, but is locked within the grid by adsorption.

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5.1 Polyurethane grouts

5.1.1 General

Polyurethane grouts (PU-grouts) are reactive plastic polymers having a widerange of properties for practical applications. Polymers are giant molecules thatare produced by joining smaller molecules (monomers) in a so called step growth(or condensation) polymerisation into e.g. polyurethane products. Products withrepeating units of NHCO2 are called polyurethane. A simple example reaction isshown below:

CH3-N=C=O + HO-CH

2-CH

3=> CH

3-NH-CO-O-CH

2-CH

3

Isocyanate + Alcohol => Urethane

The reaction products may be rigid or soft, pore free or foamed up to 30 times thevolume of the liquid components and the reaction time may vary between secondsand hours. The viscosity of mixed product, before reaction has started and alsothe speed of reaction, are both quite sensitive to temperature. There are productsfor practical application to be injected as a single component, as well as two-component systems. The properties of a product are mainly governed by thechoice of different basic raw materials. Most systems can be modified by the useof added catalysts and other chemicals that influence the behaviour of the product.

The very wide range of possible PU-grout properties offers an advantage to thespecialist, to tailor make a material for specific purposes. For the normal enduser, this complexity can be quite frustrating, because it will be difficult to sortout which commercial product is the best one for an intended application.

The normal way to offer some flexibility, without complicating matters too much,is that manufacturers will offer a limited number of standard products, with a setof properties for a range of typical situations. On the basis of such a palette ofstandard products, it will be possible for solving special problems, to addmodifications, by involving specialists on the job site.

The polyurethanes are formed by reaction of two components:

Polyisocyanate (Diphenylmethane-diisocyanate, or abbreviated “MDI”). (Thereare also other isocyanates available, but these are more hazardous and shouldnot be used for injection in any underground project).

Polyalcohols (abbreviated “polyol”)

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The structure of a polyurethane molecule created from polyglycol is illustrated inFigure 5.1.

CH2NC

O

N

H

C

O

O CH2 CH2 OX

n

Figure 5.1 Polyurethane molecule

One very interesting part of the reaction is the effect of water. If some water isadded to the polyol component, or the mixed components are meeting waterafter injection, a part of the isocyanate will react to polyurea and carbon dioxide(CO2). This reaction takes place in parallel to the formation of polyurethane andthe gas generates trapped bubbles, causing the formation of a closed cell foam.

In most cases under ground, there is a need of combined effects from an injection,like water flow cut-off and ground consolidation. The cost of materials is alsoimportant. The best consolidation is reached when there is very little foamreaction, but this will reduce the penetration into finer openings and the volumecost becomes high. At the other extreme, a very quick foaming to several timesthe original volume, will produce a low strength grout, that may be very effectivefor an initial cut-off of running water, but with little consolidation effect. A veryporous grout will also not seal completely and subsequent water pressure buildup, may compress the foam and increase the leakage again. The volume costdrops with the foam factor. The foam formation has the effect of self-injection ofthe PU-grout, because the CO2-pressure developed can be up to 50 bar(temperature dependent). The penetration of the grout is therefore not onlygoverned by pump pressure and by the product viscosity, but is also very muchinfluenced by the foaming pressure.

The properties of the foam created will depend on the local conditions. Whenfree foaming produces a volume increase of 30 times, in the ground the restrictedvolume increase will create pressure and less expansion. A typical averagevolume increase in rock injection at low pressure, is more like 5 to 10 times.

Polyurethane products have typically a high viscosity, which is a limiting factorfor permeation into the ground. At room temperature a typical product viscosityis 200 cP, but it is possible to get as low as 100 cP. If the products are diluted bythe addition of solvents it is possible to come down to about 20 cP, but solventscan cause health problems and environmental problems under ground.

5.1.2 MBT PU-products

See Chapter 11 on MBT injection materials.

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5.1.3 Pumping equipment

For 2-component PU it is necessary to use a custom design 2-component PUpump. These are normally prepared for 1:1 ratio of the A and B components (byvolume) and the whole set-up all the way up to the packer is showndiagrammatically in Figure 5.2.

To packer

Static mixer

Non-return valve

Pressure release

Pump D 200.2.21

Component A"White"

Component B"Black"

Polyol Isocyanat

valve

Return valvefor flushing

Figure 5.2 Pump and other accessories for 2-component PU

5.2 Silicate grouts

Sodium silicates have been used for decades as soil injection grouts. There arealso examples of silicate injection in rock formations. The main advantage ofsilicate grouts is the low cost and the low viscosity. It may also be added thatapart from the pH of typically 10.5 to 11.5 (causing it to be quite aggressive),there are small problems with working safety and health. Silicates are used forsoil stabilisation or for ground water control.

Liquid silicate (also called waterglass) is produced by dissolving vitreous silicatein water at high temperature (900 °C) and high pressure. The liquid is laterdiluted by water to reach a viscosity level that can be used for injection purposesin soil and fine cracks in rock. A normal injection grout will have a viscosity ofabout 5 cP and the gel produced is water rich, weak and somewhat unstable.Some syneresis will take place after gel has been formed in the ground (releaseof water from the gel and some shrinkage). Because of the low gel strength itwill have limited resistance to ground water pressure, especially in cracks andjoints that are relatively large. This can be seen in rock injection locally, wherechannels may be some cm wide, by a slow extrusion of gel over time.

The liquid silicate needs a hardener to create a gel. Acids and acidic salts willcause such gel-formation (like sodium bicarbonate, sodium aluminate), but todaynormally proprietary chemical systems will be used, showing much betterpractical properties with improved quality of the final grout. These products aremostly methyl and ethyl di-esters.

54

If the grouting is done as a ground water control of a permanent nature (severalyears), then silicates cannot be used. The syneresis is one of the problems insuch an application, that can lead to new leakage channels over time, but alsothe chemical stability is questionable in many cases. For temporary groundwater control for some months it will mostly be acceptable. In rock injection itwill often be necessary to do cement-injection as a first step, to fill up the largerchannels. The low pH cement-environment is very unfavorable for the durabilityof a silicate grout.

5.3 MBT colloidal silica

This product has no resemblance to the silicate systems described above. Thecolloidal silica is a unique new system with entirely new properties and caneven be considered more environment friendly than cement.

See Chapter 11 on MBT injection materials.

5.4 Acrylic grouts

The acrylic grouts came in use already 50 years ago and for cost reasons thesewere based on acrylamide. The toxic properties of such products have over theyears stopped them from being used. The last known major application was inthe Swedish Hallandsasen tunnel, where run-off to ground water caused pollutionand poisoning of livestock. However, it is not necessary to include this dangerouscomponent in an acrylic grout.

Polyacrylates are gels formed in a polymerisation reaction after mixing acrylicmonomers with an accelerator in aqueous solution. In the construction industry,acrylic grouts are used for soil stabilisation and water proofing of rock.Polymerised polyacrylates are not dangerous for human health and theenvironment. In contrast to that, the primary substances (monomers) of certainproducts can be of ecological relevance before their complete polymerisation.Injection materials polymerise very quickly - as a rule within some minutes.Before the monomers completely polymerise, a considerable amount can bediluted by the ground water, subsequently leading to contamination.

Because of such effects in practical injection works underground and becauseof the working safety of personnel, the use of products containing acrylamide(which is a nerve poison, is carcinogenic and with cumulative effect in the humanbody) must be avoided.

Products are available that are based on methacrylic acid esters, usingaccelerator of alconal amines and catalyst of ammonium persulphate. Theseproducts are in the same class as cement regarding working safety and can beused under ground, provided normal precautions are taken.

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Figure 5.3 MEYCO MP 301 injected in sand

Acrylic gel materials are very useful for injection into soil and rock with predominantlyfine cracks. Normally such a product is injected with less than 20% monomerconcentration in water and the product viscosity is therefore as low as 4 to 5 cP.This viscosity is kept unchanged until just before polymerisation, which then happensvery fast. This is a very favorable behavior under most conditions. The gel-timecan typically be chosen between seconds and up to an hour.

The strength of the gel will primarily depend on the concentration of monomerdissolved in water, but also which catalyst system and catalyst dosage that isbeing used. The gel will normally be elastic like a weak rubber with a strength ofabout 10 kPa at low deformation. An injected sand can reach a compressivestrength of 10 MPa.

If a gel sample is left in the open over time under normal room conditions, it willloose the adsorbed water trapped within the polymer grid, shrink and becomehard. If placed in water, it will swell again and regain its original properties. Inunderground conditions this property of an acrylic gel will seldom representany problem, but be aware that if an unlimited number of drying/wetting cyclesmust be assumed, then the gel will eventually disintegrate. The chemical stabilityand durability of acrylic gels are otherwise very good.

5.4.1 MBT acrylic products

See Chapter 11 on MBT injection materials.

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5.5 Epoxy resins

Epoxy products can have some interesting technical properties in special cases,but the cost of epoxy and the difficult handling and applicationare the reasonsfor very limited use in rock injection under ground.

Epoxy resin and hardener must be mixed in exactly the right proportions for acomplete polymerisation to take place. Any deviation will reduce the quality ofthe product. The reaction is strongly exothermic and if openings are filled thatare too large (width > some cm) the epoxy material will start boiling and againthe quality will be reduced. Also for epoxy the viscosity is high, unless specialsolvents are used.

Working safety and environmental risk are additional aspects of epoxy injectionthat makes the product group of marginal interest for rock injection underground.

5.6 Combined systems of silicate and acrylic materials

In practical grouting it is quite normal to combine different grouts during theexecution of the works. This will normally consist in reaching a certain level oftightness by the use of cement and then to finalise by some chemical grout.However, there are also products available where different chemical systemsare combined into one commercial product.

Best known is combination of silicate and acrylic grout. The silicate componentwill lower the volume cost of the final product and the acrylic component willimprove the chemical stability, reduce the syneresis and give a much strongerand more stable gel.

The product will be handled as a two-component material, where the hardenerfor the silicate is mixed into the acrylic monomer and the hardener for the acrylicgrout is mixed with the silicate. When the two components are mixed, there willfirst be a silicate gel reaction, which is then followed by an acrylic gel formationto reinforce and stabilise the final gel.

The practical handling of such a system is a bit complicated and the use ofsuch products is therefore quite limited.

5.7 Bitumen (asphalt)

In tunnel excavation it has happened a few times that extreme water ingress isexposed locally at the face. Such inrush can be catastrophic and will in mostcases be extremely difficult to get under control or to seal off.

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It has also happened that hydropower dams expose water channels from insidethe water reservoir to downstream of the dam, causing severe water loss. Leakagelike that can be extremely difficult to seal off, because it is mostly not an option toempty the water reservoir. The water pressure is therefore always present andthe flow rate in the channels that need to be sealed, can be very high.

Typically, grouting of ordinary cement grouts in such situations is useless. Thegrout has no chance to set and is diluted and flushed out by the turbulent flowingwater. Up to a certain limit, quick foaming polyurethane can be used for waterflow cut-off, but there are situations where it will not work, especially at lowtemperature (slow reaction). From case reports it is known that a number ofvery innovative methods have been tried, like cement or concrete mixed withwood cuttings, bark cuttings, cellulose materials etc., and with all kinds ofaccelerators. Frequently failing to do the job.

As a last resort, heated liquid bitumen (asphalt) can be an alternative. Theprinciple will be to use a selected quality of bitumen (roofing grade asphalt),that heated to a sufficiently high temperature (typically 200 to 230 °C) has lowviscosity allowing easy pumping. The softening point should be around 95 to100 °C. The output must be adapted to the water flow rate, the water head andthe distance from the injection point until the downstream outlet point. However,the asphalt output may be less than 1% of the water leakage rate and still beeffective. This is totally different to all sorts of cementitious grouting, where thegrout flow rate must be able to displace the water to avoid washing out.

The ideal bitumen quality will rapidly change from an easily pumped fluid materialto sticky, highly viscous and non-fluid asphalt at the water temperature. Wheninjected into the water stream, the bitumen will rapidly loose its high temperatureand rapidly and dramatically change its rheological properties. The bitumengets sticky, will easily stop in narrow points in the water channel and can thusblock the flow.

After a blockage has been achieved, it is always advisable to place some suitablecementitious grout to ensure a permanent and stable barrier.

At the Stewartwill Dam in Eastern Ontario, Canada, two concentrated leakagezones through the dam foundation were grouted by asphalt (combined withcement) [5.1]. The work was carried out with a full reservoir (about 6 bar waterhead). The first zone, grouted in 1983, yielded 13’600 l/min water leakage andthis was reduced by more than 90%. The other zone, grouted in 1984, was9’000 l/min and was reduced to virtually nil. It is interesting to note that bothcases where executed in one day of grouting. Materials consumption was 6000l asphalt and 5.7 m3 sand (1983) and 3370 l asphalt and 2.8 m3 sand (1984). Anunsuccessful attempt in 1982, using cement and sand took 2 months andconsumed 5600 bags of cement plus 73 m3 sand.

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The specialist contractor FEC Inc. carried out injection with asphalt in PleasantGap [5.2], near State College PA, USA. The grouting was running over 5 shiftsand Figure 5.4 shows one of the water-flow exits after the 4th and the 5th shift.

Figure 5.4 Flow after 4th shift (left) and 5th shift grouting (right) (Photo P. Cochrane)

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6. BORE HOLES IN ROCK

6.1 Top hammer percussive drilling

This is the common drilling method in hard rock- and medium hard rock tunnelling.The drill rods attach to the drilling machine using coarse threads and the energyfrom the hammer blows travel through the drill rod to the drill bit at the end. Thedrilling machine delivers torque for drill rod- and drill bit rotation. The rotationspeed is in the range of 80 to 160 rev./min. For hole length greater than about5 m, the drill rods are coupled. The most frequently used borehole diameter is51 mm, but lately, 64 mm diameter has become more popular. The maximumhole length is limited to about 60 m.

Since the late seventies, the hydraulic drilling machines have completely replacedpneumatic machines. Typically, modern hydraulic machines can penetrate at1.5 to 2.0 m/min. even in hard granitic rocks. By coupling of drill rods, it is possibleto drill very long holes, but the hole deviation will limit the practical hole lengthfor injection purposes. The directional deviation depends on a number of factors,primarily the chosen equipment and practical procedures and secondarily onthe rock conditions. Holes drilled near horizontal will show higher deviation thanvertically drilled holes.

A bore hole diameter of 51 mm uses a drill rod diameter of 32 mm. The outerdiameter of the couplings are 36 mm. A bore hole of 30 m length, with standardequipment, used in jointed and variable rock and with careless drilling (meaningmaximum speed drilling with high feeder pressure from the beginning), canproduce an end point deviation of 5 to 10 m (17 to 34%). By a careful and slowstart of the hole, until the first drill rod length has entered into the rock and by aslightly reduced feeder pressure, the deviation can be reduced to less than15%. It is also possible to apply stiffeners to the first drill rod, thus further reducingthe deviation. With such equipment it is realistic to achieve deviation around5%. One disadvantage with stiffeners on the drill string, is problems of groundseizing in poor ground. The risk of getting the drill string stuck in the hole issubstantially increased.

Figure 6.1 Atlas Copco COP 1838 hydraulic drifter machine (photo Atlas Copco)

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Using drilling machines of the latest design like the Atlas Copco COP 1838(Figure 6.1), the drilling capacity with 64 mm diameter drill bits is about 2 m/min.Such diameter allows the use of drill rods of diameter 38 mm. The stiffness ofthis system is substantially improved compared to the above and the holedeviation is around 5% without any special equipment or technique. Onedisadvantage is the need for bore hole packers of increased diameter. The costis higher and the problems of packer sealing in poor ground and at high groundwater head are quite a bit increased. A 25% increase of hole diameter, gives a57% increase of axial force on the packer from the ground water- or injectionpressure. It also means that the cement quantity spent for simply filling theborehole volume of one 30 m injection round of 25 holes, increases from 2200 kgto 3500 kg.

A popular compromise is the use of 54 mm diameter drillbits with drill rods of35 mm and couplings of 38 mm diameter. This is today the preferred solutionfor long hole probe drilling and injection drilling.

For the drilling of injection holes it isimportant that the borehole is ascircular as possible and with the correctdiameter. The packer will then have thebest possible chance to seal the holewithout problems. From experience itis evident that the drill bits with a (+)configuration of the carbide inserts givethe best hole circularity at the leastdeviation (see Figure 6.2). Both buttonbits and bits with a (X)-configurationtend to more easily produce ovalshaped holes. Furthermore, especiallythe button bit will more rapidly showdiameter wear and it may be producingtoo narrow holes for the packer, longbefore it would otherwise be worn out.

Figure 6.2 Drillbit for good borehole roundness and small deviation (photo Atlas Copco)

To achieve high productivity and good economy, drilling of probe holes andinjection holes of more than 5 m length, will require hydraulic equipment for thehandling of drill rods, including coupling and decoupling. This is available offthe shelf from most equipment manufacturers. It should be noted that it is alsoa must from a safety point of view, if the ground water head is above about5 bar (theoretically 100 kp axial force on a 51 mm diameter drill bit). At waterheads above this level, all manual handling of the drill string would be verydangerous and often not possible.

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For high productivity percussive drilling the water flushing for removal of thedrill cuttings is very important. When this drilling method is used for injectionbore holes, proper flushing is even more important, to reduce the risk that finematerial may be clogging joints and cracks (that shall afterwards be injected).Remaining rock cuttings may also interfere with the packer seal. Typically, about5% of the produced cuttings are less than 5 mm grain size when drilling in agranitic gneiss. Very likely, the quantity of fines will increase in softer rocks. Asecondary grinding of particles arises from the rotation of the couplers and thedrill rods and friction against the bore hole walls. This secondary grinding andthe risk of squeezing fines into joints and cracks is greatly reduced by sufficientwater flushing.

6.2 Down the hole drilling machines

This technique is also a percussive drilling method, but the drilling machineworks directly on the drill bit and follows the bit into the borehole. The drill rodsare there for feeder pressure, rotational torque and to convey the flushingmedium. Since the hammer blows are always directly on the drill bit, longboreholes will not reduce the energy delivered at the drill bit. Drilling rate istherefore not much influenced by the hole length. Typical rotation speed is 10 to60 rev./min.

The typical bore hole diameter range is 85 mm and larger. The reason whysmaller diameter is not available is the necessary space for the machine. SeeFigure 6.3.

Figure 6.3 Down-the-hole machine (illustration from SECOROC)

For drilling of injection holes in underground works, this method is not normallyused. In special cases it may be considered. If the greater hole diameter is ofbenefit; if a long hole with small deviation is required; or if it is necessary to usea casing for hole stabilisation, this drilling method may be useful. This drillingmethod, as part of the ODEX system (Atlas Copco), allows a steel pipe casingto be fed into the hole in parallel with the drilling. When the hole has reachedthe final depth, drilling machine and drill bit can be withdrawn by counter-rotatingthe bit, which reduces its diameter sufficiently for retraction. The system isexpensive and slow, but elegant for certain purposes.

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6.3 Rotary low speed drilling

Rotary drilling works by point crushing under the drill bit, due to the rotation andaxial feeding. The method is not efficient in hard rock and the minimum diameternecessary makes it unsuitable for injection drilling.

6.4 Rotary high speed, core drilling

Core drilling is also a rotary drilling method, but the drill bit is a cutting tool (notcrushing). The drill rods are steel pipes and the drill bit is a ring shaped bit withdiamonds as the cutting material. Feeding pressure and rotation torque isproduced by the drilling machine at the hole opening. The operations are normallyhydraulic, while the machine is typically powered by electricity.

Core drilling is not used for normal injection drilling, but for investigations aheadof the tunnel face and for special case injection at greater depth. The drillingproduces a core of rock material that is retrieved from the bore hole for inspectionand geological logging. Normal hole diameters are 45-56-66-76 and 86 mm.Hole lengths in the range of 300 to 500 m are possible. Up to about 100 mlength, depending on rock conditions and equipment, the drilling capacity willbe up to 5 m/h. The deviation will be in the range of 2-3% for short holes (<15 m)and around 5% for long holes.

Core drilling tends to produce round and smooth holes and typically the cloggingof cracks and joints is reduced, compared to percussive drilling. The cost andtime needed for core drilling is still much higher than for percussive drilling andit is therefore only used in special cases.

6.5 Example solution for drill and blast excavation (tunnels and shafts)

Figure 6.4 Drilling jumbo Atlas Copco Rocket Boomer (photo Atlas Copco)

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Shafts are in many respects the same as tunnels (except for the fact that theyare vertical or very steep) from an injection viewpoint. The necessity to controlground water is higher than in a tunnel, because water ingress very quicklycreates problems at the working face (the shaft bottom). Probe drilling to detectwater bearing zones before they become a real problem in the shaft is thereforeessential.

The following is an example of procedures for the systematic pre-injection aheadof tunnels or shaft faces to be excavated by drill-and-blast. The describedapproach is based on the use of the Rheocem® microcement system withsupplementary chemical products (MEYCO® MP 355 /A3 2K quick foamingpolyurethane and MEYCO® MP 320 silica grout) and on experience of similaroperations over recent years (2K means 2-component).

The example is a tunnel with a diameter of 5.5 m with access through a shaft of10.7 m diameter, where both must be sealed. The average ground permeabilityis k = 3 x 10-5 m/s and the injection should bring it down to k = 5 x 10-7 m/s. Thisis a relatively strict requirement and consequently, systematic pre-injection mustbe executed and no effort is done to probe drill to decide about injection basedon the findings. There are many situations where a more relaxed approach willperform adequately.

6.5.1 Drilling of injection holes

Drilling of the boreholes shall be done with a 51 mm drill bit preferably using ahydraulic drilling rig for maximum efficiency and control. During drilling, anyweakness zones and areas containing pressurised water are registered manuallyand noted in a special drilling record by the shift supervisor. Drilling of injectionholes must be done with water flushing of the drill bit. A suitable drilling jumbo isshown in Figure 6.4, but there are many alternatives available and also units forlarger tunnel cross sections.

All holes generally have a length of 20 m. By drilling and injecting into 20 m holelength and repeating the process every 10 m the risk of exposing unsealedundetected larger leakages by blasting are close to nil. This will be important toensure that ground water flow of uncontrolled magnitude into the openings isavoided. By a 100% overlap of injection fans the quality of the injection work willbe good.

All holes are generally drilled at theoretically about 11° out from the shaft ortunnel direction, although other orientations may be appropriate for particularsituations and/or rock conditions. The number of holes is shown in Figure 6.5.Additional holes may be drilled out from the centre of the shaft/tunnel if considerednecessary to achieve water tightness of the face. See Figure 6.5, which showsthe tunnel and the same set-up would apply in the shaft, only that more holeswould be needed (larger diameter) to get about the same hole spacing.

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Figure 6.5 Full overlap systematic pre-injection.

All holes must first be flushed with water in general at approximately 10 barpressure before injection commences.

Flushing must be done thoroughly by introducing a stiff PVC hose to the bottomof the hole which is then slowly withdrawn while flushing. Flushing is importantto get rid of all the drilling sludge and fines which may otherwise block theopening of the cracks. See also Figure 6.8 and about cleaning of holes later inthis Chapter. In weak rock conditions, with the risk of collapse of the holes, orholes where the measured ground water backflow is greater than 10 l/min. fromthe hole, flushing is not carried out.

6.5.2 Packer placement

Packers are placed between 1.0 and 3.0 m depth into the borehole, adjusted tothe ground conditions and the locations providing a good sealing. In extremelypoor ground, the grouting in of stand pipes of steel or plastic may be necessary.

In holes that are yielding ground water backflow the packer should be placed assoon as possible and the valve should be closed, to minimise the ground waterdrainage into the excavated opening.

6.5.3 Water pressure testing

Water pressure testing of boreholes is not required as a routine activity. Thelong time spent in comparison to the information value produced is the mainreason for this. Especially when using Rheocem® microfine cement at a fixedw/c-ratio, which can cover a wide variation in ground conditions, there is nogood reason to invest time and money in such measurements.

6.5.4 Choice of injection materials

Based on the expected ground conditions the type of Rheocem® must be selectedas the primary injection material. Boreholes yielding ground water inflow of morethan 5 l/min must be cement injected in any case and also all primary stageboreholes.

SP

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Depending on ground conditions and the required level of maximum groundwater leakage into the underground openings, chemical grout by MEYCO® MP320 silica grout may be necessary as a supplement. In such a case this productshould be used in the secondary stage boreholes (unless ground water inflowin individual holes is too large, as stated above).

Inflow of ground water through joints and cracks in the face or elsewhere (not inthe boreholes), may cause problems of grout washout and backflow. Suchproblems can be solved by injection of quick foaming polyurethane MEYCO®

MP 355 /A3 2K. This product is very fast (and adjustable by addition of anaccelerator) and can be used as a temporary flow blockage. Also the acceleratorused in the Rheocem mix can be an alternative as stated below.

6.5.5 Mix design for Rheocem grouting

Rheobuild 2000PF: 1.5 - 2 % by weight of binderUsual w/c ratio: Rheocem 650, 650SR, 800 and 900: 1.0

The w/c-ratio of 1.0 allows a non-bleeding grout, still with a very low viscosity ofabout 32 seconds Marsh cone flow time. This grout mix design should be keptconstant and only particular special conditions will require an adjustment suchas extremely large crack openings and lower w/c-ratio.

In cases the of uncontrolled spread of the grout or backflow to the shaft/tunnelthe MEYCO® SA160 can be added to the standard mix, by dosage at the packer.

6.5.6 Accelerated cement grout

The MEYCO® SA160 can shorten the curing time of the grout to minutes whichallows an early re-commencement of excavation operations even at high groundwater pressure and large fissures.

The normal dosage of the MEYCO® SA160 is between 1 - 5 % by weight of binder.

MEYCO® SA160 must be added at the packer by a separate dosage pumpdelivering through a specially designed non-return valve. See Chapter 4 Cementbased grouts, Accelerators for cement injection.

6.5.7 Injection pressure

The injection pressure is important for the success of the injection and needs tobe as high as conditions allow. This is one of the advantages of injection aheadof the face (compared to post-injection) and should be utilised fully.

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As noted above, relatively high pressure injection is generally possible with thepre-injection approach because injection is made into undisturbed rock ahead ofthe tunnel face. The available pumping equipment should therefore be capable ofproducing controlled pressure of up to 100 bar.

However, situations can arise where other factors influence the choice of injectionpressure and the methods of control. Some typical special measures are givenbelow:

6.5.8 Special measures

Special measures should be adopted for injection operations where eitheradjacent works are less than approximately 10 m away from the point of injectionor overburden is less than approximately 10 meters. Very weak or broken groundmay also require special measures.

• Where necessary, the following typical special measures can be adoptedas appropriate:

• Injection pressures must always be controlled by monitoring of the linepressure and pre-setting an appropriately low pump cut-out pressure.

• The grout take per hole can be limited to less than the general maximum,if the pressure comes above a certain limit. Because of the non-bleedingcharacter of the Rheocem® grout and its fast gelling when pumping stops,it will remain in place and permanently fill the occupied volume. A grout torefusal technique for consolidation of the grout is not necessary whenusing Rheocem®.

• There are a number of special measures available for the protection ofexisting tunnel linings or other structures in close proximity to the injectionarea. In summary, these measures include:

• Predetermined pressure cut-out on pumping pressure

• Predetermined limit of grout volume per hole

• Predetermined limit of injection time per hole

• Controlled setting time of the grout

• Temporary pressure relief

• Continuous visual monitoring with telephone or radiocommunication to the injection supervisor during carefullysupervised injection

Measures such as these have been used previously to control pre-injectionoperations where, for example, overburden has been as low as 4 metres (OrmenWater Tunnel, Stockholm).

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6.5.9 Injection procedure

Always start the injection in the lowest hole in the face (tunnels) and progresssuccessively towards the roof until all holes are injected.

Unless special measures are required, the injection on an individual borehole iscompleted when the amount of Rheocem® grout going into the hole is less than3 litres per minute at the maximum pressure specified. (Maximum pressure hasto be measured and maintained over a period of at least 2 - 5 minutes.), orwhen more than 1000 kg has been injected.

In the case of chemical injection by MEYCO® MP 320, an individual hole isfinished when a maximum pressure of 30 bar has been reached (at a flow ofless than 1 l/min for 5 minutes), or the total quantity has reached 500 kg.

In cases where backflow leakages occur directly out of the rock surface, useRheocem® with MEYCO® SA160 to block it, or use quick foaming polyurethaneMEYCO® MP 355 /A3 2K.

If during the injection process two or more holes become inter-connected, closethe injection packers in the connected holes. Multiply the amount of groutspecified with the number of connected holes before completing the injection.

6.5.10 Injection records

During injection the following parameters should be recorded by the supervisorin the injection record:

• Injection material and mix design

• Pressure at the beginning and the end of each injection

• Injection time per hole

• Flow of water

• Material consumption per hole

• Number of holes

• Surface leakages

• Inter-connection of grout between holes

6.5.11 Cement hydration

Packers can be removed from the holes 1.5 - 2 hours after completion of theinjection and drilling of secondary stage holes (or drill and blast holes) can start2 hours after completion of the injection of Rheocem®.

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Where the injection has been done with grout containing MEYCO® SA160or with w/c-ratio < 0.7 packers can be removed from the holes approximately40 - 60 minutes after completion of the injection. Drilling of new holes in thiscase can start 60 minutes after completion of the injection.

In the case of silica grout MEYCO® MP 320, a minimum of two times the geltimeshould be allowed from the completion of injection until next drilling.

6.5.12 Other relevant issues

All preinjection works shall be carried out under the supervision of aSuperintendent with relevant qualifications and experience.

The Contractor must submit a complete method Statement (MS) for thepreinjection works, in advance of the start of injection. The MS shall containinformation about, but not necessarily be limited to, the following:

• personnel and supervision, with lines of decision-making

• drilling and flushing methods and equipment

• type and use of packers

• materials, mixes and quality control procedures

• proposals for site trials

• injection plant presentation

• procedures and forms of record keeping

• integration of systematic pre-injection into the construction cycle

• safety instructions

All pipes, hoses and connections shall be designed to withstand the maximumpressure to be applied and shall be drip tight.

The mixer shall be of the colloidal mixer type, with a rotor speed of a minimumof 1500 rpm. After the mixer a holding tank shall be provided, equipped with anagitator slowly running at all times. The pump shall be a duplex piston typeoperated hydraulically, to allow the pre-setting of the grout flow and the maximumpressure.

Holes injected by MEYCO® MP 320 shall be filled by cement grout from thepacker location to the opening. This grout shall be of a low w/c-ratio type suitablefor grouted rock bolts.

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6.6 Solutions for TBM excavation

Hard rock TBMs are open machine layouts, with just a part roof shield over thefront of the machine. The system is designed for fast advance and the economyof the project depends entirely on the rate of advance. Typically, hard rockconditions will demonstrate stable and good ground for a major part of thetunnel. However, short sections of crushed shear zones with clay and gougematerial may cause serious time delays. Spiling rock bolting is very efficientunder such circumstances, provided the fully grouted rebar bolts can be placedefficiently, which requires proper drilling equipment.

Environmental restrictions are also a part of TBM tunnel excavation projects.Even such tunnelling may require a strict ground water control, because of thenormal potential consequences on the ground surface.

To take advantage of spiling rockbolts and to execute pre-injection, it is an obviousprerequisite to be able to drill the necessary boreholes in the right positions andat the correct angle. In drill and blast excavation this is simple, but in TBMprojects it has repeatedly turned out to be difficult. More than once owners haveaccepted bids containing reassurance from the contractor that the drilling methodwill be sorted out later. Experience shows that if “later” means after start of theTBM operation, it is often too late.

6.6.1 The Oslo Sewage Tunnel System

The tunnel system consists of about 40 km of sewage transport tunnels and anunderground sewage treatment plant. Construction was undertaken around 1980.The tunnels were constructed by TBM to avoid the vibration problems whenpassing below an urban area. Pre-injection was mandatory because a majorpart of buildings and infrastructure are founded on marine clay. Even a minorlowering of the pore pressure in the clay basins would cause settlements up toseveral hundred meters away from the tunnel alignment.

The first contract let was based on a 3.5 m diameter hard rock Robbins TBM.The contractor stated that the probe drilling and injection drilling would be solved“later”. The method finally adopted was very poor. The TBM was backed up acouple of meters, people and equipment were passed through the cutterheadand drilling was carried out by manually operated pneumatic jackleg drills. Thissystem was grossly unsatisfactory and caused the owner to reject all bids forsubsequent project sections, if the detailed pre-injection drilling solution wasnot included and acceptable up-front.

The largest single tunnelling contract covered 14.2 km of 3.5 m diameter TBMtunnel and a 900 m drill and blast access tunnel at Holmen. The two RobbinsTBMs were manufactured to accommodate two hydraulic booms with MontabertH 70 hydraulic borehammers. The feeder length was 10 feet (3 m).

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During planning of the works, it was found that all components had to be adaptedto integrate with each other. This included the TBM. The final outcome provided17 locations around the periphery where boreholes could be started. From eachlocation drilling could be carried out in variable directions. The starting points tocollar the holes were 3 m behind the face.

The equipment layout can be seen in Figure 6.6. The normal borehole anglerelative to the tunnel contour was 4°. By drilling 27 m boreholes, losing 3 mbetween the starting point and the actual face and by 4 m overlap to the nextdrilling, a net length of 20 m tunnel was pre-injected per round. This is shown inFigure 6.7.

Figure 6.6 Tailor made hydraulic drilling equipment mounted on hard rock TBM

Work in the tunnel was organized in two shifts per day; each shift was 7.5hours. The routine drilling of four 27 m long holes normally required 3 to 4 hours,including setup and clearing away. The injection time was highly variabledepending on the quantities injected. It is therefore no surprise that weekly faceprogress also varied accordingly. The average weekly advance was about 60m.

Figure 6.7 Borehole length and net coverage per grouting stage, plan view.

The total cost of pre-injection, including drilling ahead, was 38% of the totalContractor’s cost per meter of tunnel.

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6.6.2 The Hong Kong Sewage Tunnel System

More than 1.5 million cubic meters of wastewater is being discharged into VictoriaHarbour per day and to reduce the pollution the Government has decided toconstruct a deep sewage collection and conveyance system with a total lengthof about 70 km. The Stage I include 23.6 km tunnels to convey sewage collectedfrom the northeastern areas of Hong Kong Island and Kowloon to StonecuttersIsland. A treatment plant has been built to purify the sewage. After treatment,the effluent will be disposed via a submarine outfall to the western approach ofthe Victoria Harbour.

Construction of the Stage 1 works started in April 1994. The deep tunnelconveyance system and the outfall, which are 2.2 m to 5.0 m in diameter runningat depths between 76 m and 150 m below sea level, was excavated by TBM.The value of the works was about 270 million USD.

Skanska International Civil Engineering AB was the main contractor for contractDC/96/20 including 3580 m of TBM tunnel. Grouting was carried out to limitinflow of water for safe tunnel boring and to enable permanent concrete liningto follow. The aim was met by pre-grouting supplemented by post-grouting whereneeded.

The method reached after a long period of optimization was to executepre-grouting when probe holes yielded 2 lit/min/m. Supplementary post-groutingwas also used. Key points in the procedure was:

• Stable grout (< 5% bleeding)

• Micro cement with admixture to allow low viscosity (Rheocem® 650)

• Optimized drilling pattern

6.6.3 Comments on drilling and injection equipment

Drilling ahead of a hard rock TBM is difficult because of the very limited availablespace close to the tunnel face. The TBM itself occupies almost all the volume forthe first about 15 meters.

The solution showed from the Holmen Site was established after elaboratedesign work including the TBM manufacturer’s design staff. The main beam ofthe TBM was elongated by about one meter, to accommodate the hydraulicbooms. Even with this solution the starting points for probe holes or injectionholes are about 3 m behind the face. This distance is critical to the performanceof the total set-up.

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There are examples of starting points at greater distances like 6 m, Skjeggedal[6.1], and 9 m from the face. The last figure as given by Avery [6.2] from theInland Feeder Project, Arrowhead East tunnel, Los Angeles, where they finallydecided to drill through the cutter head itself. In the Hong Kong sewage projectmore than 10 m distance was tried but later improved as a matter of necessity.It is obvious that the starting point distance multiplied by the number of holes,gives the meters drilled and wasted per round of drilling. Lost time and additionalcost will soon become critical with increasing starting point distance.

Injection often requires pumping pressures of more than 30 bar. Because thedrilled holes are started in the wall at typically 4° to 8°, the distance to theexcavated tunnel wall is very small. To avoid a blowout and grout backflow intothe tunnel, the only safe solution is packer placement in front of the actual facelocation. This may require a packer placement depth of more than 10 m on aroutine basis, which is very time consuming and expensive.

6.7 Cleaning of holes

Holes drilled for injection of grout must be cleaned properly. The effect of notdoing this can be a rapid blockage of the intersected water bearing channelsalready in the first few mm of the channel, measured from the borehole wall.This can happen when sludge and rock cuttings from the drilling process areforced into the openings by the injection material and the pumping pressure.The effort spent in drilling the borehole may in a worst case be more or lesswasted.

An investigation carried out in Norway in 1982 and reported at the yearlyNorwegian Rock Blasting Conference gives an indication of the importance ofcleaning. Unfortunately, the volume of tests is low and therefore not conclusive.However, the results are fully in line with practical experience from injectionworks in rock.

A custom designed diesel powered equipment was used to provide a cleaningjet pressure of 250 bar. The water was pumped through a high pressure hose toa nozzle with water jets pointing at 45º back along the hose and 90º radially.With this configuration the nozzle was self-propelled forward into the hole andcould be pulled out again by the flexible hose.

The pump was also used for water pressure testing (WPT) and to executehydraulic splitting of the boreholes (if no water take was measured at normal 10bar testing pressure), by providing water pressure up to 350 bar. The equipmentdiagram is shown in Figure 6.8.

For cleaning of boreholes and if hydraulic fracturing, the pump would be drawingwater from the buffer tank. When executing WPT, the valve would close to thebuffer tank for water supply only from the graded measuring tank.

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During high pressure cleaning of boreholes the valves A and B would be closed.The nozzles were designed to give 250 bar pressure at a flow rate of 40 l/min.For safety reasons the water supply hose had a foot operated valve giving freelow pressure water flow when not operated. When ready to start flushing theoperator would step on the valve and all the water would go to the flushingnozzle.

Figure 6.8. Equipment for borehole flushing, WPT and hydraulic fracturing

For hydraulic fracturing the foot-valve was removed, valve A closed and valve Bopened. The fixed nozzle in series with valve B was designed to give 150 bar at40 l/min if the borehole was tight. Other nozzles could be used if a highermaximum pressure was required.

For WPT the valve B had to be closed and valve A opened. The nozzle in serieswith valve A was adjustable and could be used for adjustment of the pressure(depending on water flow into the borehole), to keep it as close as possible to10 bar (which should be used for WPT).

The holes were cleaned first by the traditional method of water and compressedair flushing through an open hose pushed to the bottom of the hole. The typicalhole length was 10 to 15 m. After this normal way of cleaning WPT was executedwith the described equipment.

The next step was high pressure cleaning and the nozzle was self-propelled tothe bottom of the hole and pulled out three times. Then another WPT was carriedout. Tight sections were subjected to hydraulic splitting to see if it was possibleto create permanent connections usable for injection.

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The equipment turned out to be very practical and the cleaning process could becarried out much faster and more efficiently. The equipment was furthermore wellsuited for WPT and for hydraulic splitting. In the two locations where there waswater take measured with normal cleaning, the measured values increased my8.2% and 55.3% after high pressure cleaning. In places where there was noleakage, the hydraulic splitting created channels yielding up to 3.04 Lugeon.The quantity of additional dry material washed out of the already cleaned holesvaried from 0.5 kg to 40 kg per hole. The maximum quantity came from a holeintersected by a clay seam.

6.8 Packers

When a hole has been drilled into the rock formation for the purpose of injectinga grout at high pressure, a tight connection (seal) between the pumping hoseand the borehole is needed. The normal way of achieving this is by the use ofso-called packers.

The typical packer consists of a pipe with a coupling in the tunnel end and anelastic expander that can be inserted into the hole and expanded against theborehole wall. The expander will anchor the packer in place so that the injectionpressure is not forcing it out of the hole and it shall also seal off the pressurisedsection of the borehole from the tunnel side. The injection pump hose is hookedup to the pipe and the pump can be started.

There are a number of different packer types available and some examples areshown just for illustration. Most manufacturers produce in principle the sametypes of packers, but they may be quite different in quality, dimensions andtechnical details. Packers must be selected for each individual project based onground conditions, availability, price and a number of other factors.

6.8.1 Mechanical packers (expanders)

The typical mechanical expander is meant to be re-usable and works in principleas shown on Figure 6.9. The diameter of the rubber expander has to be in acertain relation to the bore hole diameter and the maximum expansion available.The manufacturers will give detailed information about this. Normally, suchpackers can be delivered in different standard lengths, typically from 1.0 m to5.0 in steps of 0.5 m, but the user can also produce his own pipes locally andmake any suitable length. For very deep packer placements it is normal to useconnectors to join standard pipe lengths like 3.0 m.

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Figure 6.9 Mechanical borehole packer

At the end of the packer-pipe it is normal to fit a ball valve or similar. When theinjection is complete, the ball valve can be closed and the pump hosedisconnected (see Figure 6.10). Without the valve pressurised grout would flowback into the tunnel. The valve must remain closed with the packer in place untilthe grout has set sufficiently to keep the ground water pressure. The packermay then be removed and cleaned for re-use in a different hole.

Figure 6.10 Ball-valve and hook-up for the grout hose

The cleaning of packers of this type can be quite time consuming and if they arenot removed at the right time, it may become impossible. Loss of some of thepackers is therefore normal. If very fast setting grout must be used, or withPolyurethane grout, cleaning of packers is often not feasible or practical. Thetendency has been to use less of this traditional type packer and to use more ofthe disposable (single-application) packers.

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6.8.2 Disposable packers

For reasons given above the disposable packers are frequently a good alternativeto re-usable packers. They are working in principle the same way as there-usable, but they are constructed so that when expanded, the expansion isautomatically locked to allow removing the inner- and outer pipes used to placethe packer and expand it. The packer itself has a one-way valve to keeppressurised grout in place without backflow when releasing the pump pressureand removing the pipes.

Figure 6.11 Disposable packer with installation assembly (photo Roulunds Codan)

Such packer assemblies are illustrated in Figure 6.11 and Figure 6.12 showingfour different standard dimensions.

Figure 6.12 Disposable packers, 38 to 63 mm diameter (photo Roulunds Codan)

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The same type of packers with minor modifications can be used as normal re-usable packers (by removing the expansion lock ring and the non-return valveat the tip). It is also possible to force the non-return valve to stay open whenwanted (by inserting a short piece of pipe), e.g. to be able to detect connectionsfrom other boreholes being injected or water pressure tested.

6.8.3 Hydraulic packers

So-called hydraulic packers are expanded (or inflated) via high water pressuresupplied through a separate thin line from the tunnel to the packer location. Thepacker itself is only handled via a single pipe, which is also the grouting pipe (orhose) after the expansion. Such packers are normally longer (typically 300 mmto more than one meter), they have a much wider expansion range and they willseal better (due to the length). However, they are also substantially moreexpensive and if such packers are regularly lost due to attempted removal afterthe grout has set too much, the cost will quickly become prohibitive.

For WPT in long holes, these packers are quite practical, because they arequick to expand, deflate and move and the low risk of backflow around thepacker and the good sealing properties in poor ground are very favourable.Figure 6.13 shows an inflated packer.

Figure 6.13 Inflatable borehole packer (photo Roulunds Codan)

When it is necessary to WPT or inject shorter sections of boreholes the hydraulicdouble packer is used. See Figure 15. Here two packers are coupled in tandemat a fixed distance. When expanded in the borehole, the grout will fill the boreholeonly between the packers and only this section of the hole will be subject toinjection pressure (or water pressure in WPT procedures).

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The mechanical expanders and the disposable ones will not work properly in veryweak ground. It is difficult to make them seal without backflow, they may startsliding in the hole and sometimes they get stuck in the wrong position. A combinationof a hydraulic packer and a disposable self-locking packer can be very useful andeconomic under such conditions. This special hydraulic packer allows expansionof the disposable packer mounted in the front of it, and the hydraulic packer helpsprevent backflow and sliding during injection. After a short waiting for grout setting,the hydraulic packer can be removed, while the disposable one remains in place.

6.8.4 Standpipe techniques

There are situations where the ground is so poor that packer placement is verydifficult and the bore hole stability can also be quite a problem. Typically, thishappens in hard rock tunnelling in shear zones and highly broken ground. Whensuch conditions are combined with high water ingress at high pressure thecombination may even lead to loss of face stability and a progressive collapse.

The drilling of long holes will frequently be a problem in itself because the drillstring will easily get stuck and will sometimes break in the bore hole.

If such conditions are encountered it is important to get a safe position to workfrom (the overlap zone from previous round of grouting should normally help inthis respect). It must be avoided to improvise a shallow packer placement invery poor ground, allowing the high water pressure to get too close to the face(risk of collapse).

One of the best ways of dealing with serious problems of this type is to use theso-called stand-pipe technique. By using an over-size drill bit of e.g. 76 mmdiameter to drill to a depth of say 3 to 4 meter it will mostly be possible to inserta steel pipe of suitable diameter (i.d. > 55 mm, o.d. < 66 mm) into this hole. Thepipe must be grouted in place using a high quality shrinkage compensatedcement grout. This is easy to do by placing a packer close to the inner end of thepipe and pumping the grout into the annular space between pipe and rock, untilit appears at the bore hole collar. See Figure 6.14.

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Figure 6.14 Use of standpipe in poor unstable ground

Once the grout has set the pipe can be used to extend the hole by an ordinary 51mm diameter drill bit (as indicated in Figure 6.14). As soon as the drilling hitsserious problems of any kind, a packer may be placed safely and tightly in thesteel pipe and the drilled part can be injected. After grout setting the drilling maybe resumed for another step of bore hole deepening. The process may berepeated as required.

When the boreholes are drilled from the tunnel contour and angled outwards,the steel pipes will work like spiling rock bolts and improve stability quitedramatically. If such stand-pipes must be drilled in the tunnel face it may happenthat steel pipes cannot be used. It is then possible to place plastic pipes thesame way as described above. These do not cause any problems for TBMs orRoadheader excavators, and can be rapidly broken without damaging the cutters.

6.8.5 Tube-a-manchet

This is a technique frequently used in soil injection (mostly vertical holes) but itis not common in rock injection under ground. The principle is shown in Figure6.15, where a hydraulic double packer has been inserted into a pre-groutedsleeve pipe. The sleeve pipe is surrounded by a weak mortar often called amantel grout, which is a simple cement grout with a relatively high content ofBentonite clay. The sleeve pipe has non-return valves (rubber sleeves) at fixeddistance and these valves can be activated individually by injection pressurebetween the double packers. The mantel grout is designed so weak that it willsplit from the injection pressure and grout can flow out into the ground withoutescaping along the borehole. The packer can be moved as needed and a givenvalve can be grouted several times.

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Figure 6.15 Tube-a-manchet (sleeve pipe), principle

In tunnel injection where holes are frequently sub-horizontal, it is very difficult toensure a proper filling by mantel grout around the sleeve pipe. Grout leakagealong the hole, rather than injection of the ground is therefore often the result.

6.9 Probing ahead of the face

6.9.1 Normal approach

In tunnelling it is normal that information about the details of rock conditions infront of the face is quite limited and not so reliable. The general average conditionsmay be reasonably well known, but that is of little help if a local feature is suddenlyexposed yielding several thousand liters of water per minute at high pressure.Furthermore, the contrast between normal hard rock tunnelling conditions andthe sudden occurrence of a major shear zone containing swelling clay andcrushed rock, can be quite dramatic. When exposed without warning, this isoften magnifying the problem.

Probing ahead of the tunnel face by percussive drilling is one way of reducingthe risk created by not being prepared. Percussive drilling is not an optimalmethod for mapping of rock conditions or investigation of hydro-geologicalconditions ahead of the face. It is however, the best method available forinvestigation of water within a reasonable time- and cost frame, operating froma tunnel face. A core hole will produce a lot more information and more accuratedata, but it takes too much time to be used as a routine tool.

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In a drill and blast tunnelling operation, the equipment is already there and theadditional effort of drilling some of the blasting holes to a greater depth for probingahead, is quite limited. A minimum will be a single hole, extending some distancebeyond the blast holes. Typically, two to five holes reaching 20 to 30 from the facewill be used. The number of probe holes that are necessary will depend on thesize of the tunnel, the rock- and ground water regime and the potentialconsequences of not detected problems. A general rule is not available, butregarding water inrush risk, probability of problem detection, will increaseproportionally to the number of holes drilled, until a hole spacing of about 5 m.The risk reduction by further reduction of the spacing, will certainly be real, butwith diminishing returns.

In sub-sea tunnels, below rivers or a lakes, or anywhere with a high risk if therock cover is less than expected, the probe drilling would be targeted at morethan just detecting water. A drilling pattern for a sub-sea two lane road tunnelhas been presented by Blindheim [1.2], as shown in Figure 6.16.

Figure 6.16 Probe drilling for sub-sea two lane road tunnel1. Routine minimum probe drilling2. Additional holes in expected weakness zones3. Alternative holes in sections of low rock cover4. Overlap (minimum 8 m) for each 5th blasting round

In tunnels excavated mechanically, equipment for probe holes will be one extraunit. In roadheader excavation a small drill jumbo could be used, on any kind offull face machine, custom designed equipment must be mounted on the TBM,to be practically useful.

Percussive drilling produces bore holes in the ground and a sludge of drill cuttingsand water coming out of the hole. A trained operator or an experienced geologicalengineer can log information like changes in drilling rate, colour of sludge,changes in fragmentation of the sludge, loss or reduction of flushing water,sudden increase of water out of the hole etc., all linked to depth from the tunnel

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face. The observations must be noted in a prepared log. The interpretation of theobservations must be expressed in writing, but separated from the actual basicdata. From the observations and the resulting interpretation, decisions can bemade on possible action regarding additional drilling, execution of pre-injection,start of drill and blast etc.

One problem for visual observation of the probe drilling process, using modernhydraulic drill jumbos, is the automatic jamming prevention system. When thedrill bit goes from hard un-jointed rock into weak material, or very fracturedmaterial, the feeder pressure will be reduced and sometimes even a shortretraction will take place. These automatic system reactions to varying rockconditions are not easily interpreted by the observer.

The advantages of percussive probe drilling are the low cost, the speed ofexecution, that normally no extra equipment is required and a fairly highprobability of detecting major serious features.

The disadvantages are the dependency on the observer’s experience and thesubjective evaluation of what can be observed. It is very difficult to interpretvariations observed, other than high contrast features and the method is thereforequite crude.

When there are indications that problems of a serious nature will occur withinthe probing depth and more exact information is considered essential, acombination including core drilling is often used. This is normally chosen as anext step only after a careful evaluation, because of time and cost involved.Core drilling will produce rock samples for inspection, where the exact locationof all features can be logged. In cases where core loss occurs, this is in itself anindication of so weak material that the core has been destroyed (unless carelessdrilling or worn equipment was the reason).

Regardless whether probe holes are drilled by one or the other method, it isalso possible to use bore hole radar systems, seismic tomography, electricresistance investigations and similar sophisticated techniques. This is consideredbeyond the scope of this book and will in any case be a subject in only a verylimited number of cases.

6.9.2 Computer supported logging

One example of a commercially available computerised logging system forpercussive drilling in rock comes from Atlas Copco in Sweden [6.3]. The systemis based on the idea that the penetration rate is normally increasing in weakerrock and to some extent in jointed rock, while at the same time the torque alsoincreases. The range and pattern of drilling parameter variation, is givingindications about discontinuities, spacing and rock material strength contrasts.

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A rock quality model has been developed as a PC-software, interpreting themeasurements made by instrumentation on the hydraulic system of the drill jumbo.The drilling parameters measured and recorded on the PC are:

• Drilled hole length

• Penetration rate

• Axial drill rod thrust

• Torque

The sampling frequency of the drilling parameters can be chosen and the normalvalue has been 100 mm. When the system is used on a normal drill jumbo, afiner resolution is mostly not useful, since the bore hole deviation and theuncertainty of the exact location of the borehole starting point will be greaterthan this. Computerised drill jumbos are being used in some projects, wherethe system reads off the exact drill jumbo location from a laser beam and inputis made of the exact chainage. If this is combined with stiffer drill rods, then afiner resolution is possible and reasonable.

The graphical model software will filter and process the drill parametermeasurements and generate a rock quality scaled colour picture.

The entire analysis and presentation on screen takes only a few minutes. Therock quality shown by the colours along the bore hole can be compared betweenholes, rounds or tunnel sections, independently of drill depth, thrust etc., whichvary extensively between operators. Parallel holes can also be combined togenerate sectional rock quality maps.

This model is based on a combination of several monitored parameters, is muchmore accurate and robust than any observation method based on a singleparameter monitoring. This system is also overcoming the observational problemof the automatic drill jamming prevention system. When this system reducesthrust because of weaker material to reduce the risk of jamming, the reducedpenetration resulting, is not misinterpreted as harder rock.

Probe drilling is carried out as part of a decision-making procedure. Theinformation has to be processed and evaluated, to decide on the consequencesfor further activity at the tunnel face. Due to the high cost of time and oftenlimited possibility of providing highly qualified geological engineers at all tunnelfaces, this whole process can become expensive and with a risk ofmisinterpretation. The computer system can help reducing these problemssubstantially. By using data-communication, one design office located anywhere,may process and evaluate monitoring results from several tunnel faces andreturn the conclusions within minutes. It should be mentioned that the cost ofinstrumentation, software and PC to be able to run the system, is marginal in

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comparison to the benefits of the accurate information. The cost of an experiencedand qualified visual observer at the face could easily be in the same range, with farless accurate interpretation.

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7. HIGH PRESSURE GROUND WATER CONDITIONS

Ground water at high static head (greater than 10 bar) creating a high-flowwater in-rush creates problems in tunnel construction. A summary of experiencesfrom some Norwegian tunneling projects is presented and discussed below.

7.1 Basic problem

In hard rocks like granite and granitic gneiss with high overburden, the normalsituation is that only limited parts of a tunnel will intersect highly jointed areasproducing large water in-rush at high pressure. The problem character will varywithin a wide range, from project to project. Even smaller and more distributedinflows may add up to substantial leakage volumes.

Practical work procedures, economy, construction time and safety are aspectsthat must be considered and balanced against each other.

7.2 Features that adds to the problem

• High static head of the ground water (above 10 bar)

Ulla-Førre Project 3 to 15 bar

Kjela Project 20 to 30 bar

Holen Project 20 to 50 bar

• Large water-bearing channels intersected frequently but randomly

• Tunneling on down slope, or the access tunnel is on a down slope or througha shaft

• The problem tunneling face is on the Project critical path

• Too low pumping capacity for dewatering, poor drainage capacity

• Weak rocks or rock zones, or heavy jointing or crushing

• Salt water

7.3 Consequences for the Contractor

A normal Norwegian contract requirement is that the Contractor must cope withup to 500 l/min. inflow from one face. This figure is sometimes as high as 1000to 1500 l/min. The normal understanding is that the figure expresses the sumtotal of water inflows over the tunnel section excavated on one face. Such waterinflows are normally handled by pumping, especially when the inflows are welldistributed. Some local problems may arise, but seldom of a serious nature.

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More concentrated ingress directly at the face (a few m3/min.) at a high statichead, will often create a cost reimbursement situation, until the problem zonehas been passed. Such an unforeseen situation will cause loss of time, especiallywhen not prepared for. On short notice, the Contractor will have to providegrouting equipment, grout materials, pumps and suitably experienced staff. Whensuch conditions are encountered, the tendency is that more similar zones willfollow and that more time passes until contractual and practical solutions tominimise the problems have been found.

7.4 Consequences for the Owner

The Owner’s concerns are project progress and cost, but often the economicalconsequences may be far more serious than for the Contractor. This willespecially be the case if the face is on the critical path of a major project. Asample calculation may illustrate the point (cost in USD):

Specialist grouting Contractor with equipment 2000 per dayFace stand-still cost, main Contractor 10000 per dayIncreased interest cost, (Hydro power project 200 mio) 55000 per dayGrouting materials, packers etc. 200 per day

Total 67200 per day

If the above figures were related to a hydro power scheme, the lost revenuefrom delayed electricity production must also be added. The cost of possibledamages in the surroundings is also not included.

To keep a complete set of grouting equipment in stand-by at the job site, therental cost could amount to USD 100 per day. In addition there will be some costof storing grouting materials on site (capital cost and potential cost of waste inshelf life is running out). With this rental cost, materials cost and the above costof delay, one day saved project time would cover about one year of fully preparedstand-by. The water problem risk must be very low, not to pay this premium.

7.5 Methods

There are two ways of handling water inflow problems:

1. Pumping out of the water

2. Injection

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These methods could be regarded as alternatives, but there are good reasonsto consider them as supplementary:

• There are clear limits as to the quantities of water that can be pumpedthrough pipes, or that can be handled by gravity drainage systems, providedthat reasonable practical and economical frameworks are applied.

• The limitations are even more pronounced when considering the face area.Tunneling on a decline will experience problems already at inflow rates ofonly 1 to 2 m3/min.

• Water at a high static head may cause water jets spraying the whole facearea, causing very difficult working conditions, especially at low watertemperatures.

• If inflows have already occurred (through cracks and joints), post groutingis very difficult, costly and often unsuccessful, especially at high pressure.

• A counterpoint is: It is possible to successfully grout almost any kind ofwater bearing structure, provided that detection and contact has been madethrough drilled holes (pre -injection). The prerequisite for this is effectiveprobe drilling ahead of the face, which is a relatively simple and inexpensivemeasure.

• Pre-injection may also be costly and time consuming, particularly so, if theaim is absolute water tightness. Experience shows that an attempt to sealthe last 20% of a potential water inflow may cost more than sealing the first80%.

In conclusion to the above points:

• It may be a high-risk undertaking to excavate without probe drilling, onlyrelying on the pumps for dewatering. A drowned tunnel may be theconsequence.

• A complete sealing of the tunnel by grouting, becomes too time consumingand costly to be a feasible solution.

• A well planned use of probe drilling, pre-injection locally and pumping willnormally be the optimum solution. The risk of major water inrushes can bevirtually eliminated.

7.6 Practical procedure in high risk areas

7.6.1 Pumping system

The capacity must be chosen based on predicted and actual project conditions.The reserve capacity should be minimum 100%. When excavating on a longdown gradient, a stepwise pumping system with buffer tanks and decreasingcapacity down slope has proven efficient.

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7.6.2 Probe drilling

The safety effect of probe drilling increases about proportionally with the numberof appropriately oriented holes, within a practical range of 1 to 10 holes. Thereare examples of major water inrushes because executed probe drilling did nothit the water bearing channels. In high risk areas the minimum should be about4 holes and shafts would require more than this.

The length of probe holes can be adapted to the equipment, shift sequences,round length etc. Still, a minimum overlap should be in the range of 5 to 10 m.Probe drilling of this type can be executed by percussive equipment. Diamondcore drilling can only be a supplement in special situations, due to time andcost.

7.6.3 Injection

If large water quantities are found at a drilled depth smaller than the plannedprobe length, only 2 to 3 meters further drilling is carried out. More holes arethen drilled into the same area and injection carried out. New holes to check theeffect of the grouting are made from the same face position, if the contact depthis less than about 15 m.

If the first contact and injection was made at a depth greater than 15 m, furtherexcavation until 5 to 10 m remains can be executed to shorten the drilling forcontrol- and grouting purposes.

7.6.4 Special issues

In spite of probe drilling and pre-grouting, a risk is always there to still intersectwater when drilling a blast round. In such a situation, an extra round of groutingmay become necessary. If so, care must be exercised to avoid allowing highpressure water too close to the face. This can be achieved by placing packersas deep as possible in the hole, and by limiting the number of holes drilled. Incase of a poor and jointed rock in the face area, the risk may be high that a localrupture in the face occurs. Grouting will then become difficult, or impossible dueto flushing out of pumped materials. Experience shows that about one weekmay be lost in such a case, to establish an anchored concrete face slab, allowingcontrolled grouting to be executed.

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7.7 Practical aspects

At Holen Hydropower Scheme, Access Øyestøl (52 m2), the recorded groundwater static head varied between 20 and 50 bar. Such pressure may causequite dramatic effects in the tunnel. When drilling into a water bearing zone,frequently water, sand and fines would punch through the drill rod all the wayback into the drilling machine. Water supply hoses of normal quality leading tothe drilling machine, would break. When withdrawing the drill rod, the water jetout of a 51 mm diameter hole would easily reach 25 m back from the face. Thewater yield from a contact at 10 m depth would typically be 2 to 3 m3/min. Ameasurement made on a 45 mm diameter hole being 4.5 m long, gave 4 to5 m3/min.

To reach the depths required for safety purposes, drilling has to be executed bythe coupling of drill rods. Manual handling of the drill string against 50 bar statichead is impossible. The force exerted on a 51 mm diameter drillbit is about1000 kp. It happened accidentally, that the drill string was blown out of the holeand landed 15 m away from the face. In one example of such a blow, the front ofthe drill jumbo was hit by the drill rods, producing a very visible dent in a 25 mmsteel plate.

When high pressure ground water is expected, the drill jumbo shall be equippedwith hydraulic clamps for securing the drill string during coupling and de-couplingof rods. A last resort at extreme pressure, without such equipment, is to drivethe drill jumbo away from the face, until the drill string is free of the hole. Also, ifnecessary, when drilling more holes into the zone, drill all holes almost to fulldepth. Then couple the last one or two rods by moving the drill jumbo.

When conditions allow, it is beneficial to drill a number of holes into contact withthe water bearing zone. The pressure will then normally drop somewhat, makingit easier to place packers in the holes. Also, the effect of the first step groutingwill normally be better, compared to grouting through very few holes. Normalcements will require about 24 h hardening time, before control holes can bedrilled. Drilling too early may cause a rupture and flushing out of the injectedmaterial.

To place packers against static head of 50 bar, adaptations on the drill jumbohave to be made. The drill feeder and drill rod guides must allow handling of thepackers by the hydraulic system. Even with such a solution, it is quite complicatedto enter the borehole, due to the produced water spray and subsequent lack ofvisibility.

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7.8 Equipment

Mixing and pumping equipment must allow a pumping capacity of about 5 m3/hat 30 bar pressure, as a typical starting point. The pump must allow a minimumof 50 bar over pressure compared to the ground water static head. Hydraulicpumps should be used, since these normally allow independent control of flowand pressure. The equipment package must allow the use of fairly stiff mortars(e.g. no long and narrow suction hoses) and preferably allow particle sizes up toa maximum of 5 mm.

Couplings, hoses, valves and other fittings must be designed for the maximumpressure.

All kinds of standard mechanical rubber expanders (packers) will easily become“bottlenecks” in the system, in more than one sense. Frequently, the rubberexpander is damaged during insertion against extreme pressure, or it cannottake the load when closing the valve. The inner pipe used in packers for 51 mmdiameter holes, is often a ½” (12 mm) pipe. The pipe is weak and will also limitthe maximum particle size in the grout to about 3 to 4 mm. A long pipe of thisdimension will furthermore reduce the possible pumping capacity.

A threaded steel pipe, split like a Split Set rock bolt in one end, has proven agood alternative. The net diameter with this solution is about 40 mm. Fixing of astandpipe by quick setting mortar, combined with drilling through the pipe, issometimes a good and necessary solution (refer to Figure 6.14).

7.9 Examples

Some key facts are given below from executed tunnelling where severe groundwater problems where encountered.

7.9.1 Kjela Hydropower Scheme (South central Norway)

The access tunnel Turvelid, excavation in direction of the lake Bordalsvann, islocated close to the Europe-road E68, Edland - Haukeliseter. The access tunnelwas excavated on a decline, while the water tunnel towards Bordalsvann had aslight incline, with frequent ground water inflows. At 1800 m from the accesstunnel, the worst water ingress situation occurred.

Ground water at 23 bar static head was encountered in probe holes 6 to 7 mahead of the face. Grouting was carried out during 6 shifts and was prematurelystopped due to time and cost concerns. The next blasting round struck a waterinrush of 15 m3/min.

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Steel pipes (4 units of 102 mm diameter) were placed on the tunnel invert, fromthe inrush point outwards. The last 7 m of the tunnel was then solidly filled byconcrete (while the water was drained through the pipes). Additionally, 2 m ofconcrete plug was carried out later. Contact grouting around the concrete plugfinally brought the remaining inflow with closed steel pipe valves, down to500 l/min. When the situation was under control and a by pass tunnel had beenexcavated, about 6 months had been lost.

7.9.2 Ulla Førre Hydropower Scheme (South West Norway)

The Flottene access tunnel was excavated on a decline and the water tunnel inthe direction of Førrejuvet had some ground water problems. In a similar situationas the one described above, the Owner wanted to blast the next round in spiteof a potential ground water yield higher than the installed pumping capacity.This blasting was not executed. The Owner then instructed the Contractor toprovide increased electricity supply, extra transformer and more pumps andpipes. Meanwhile, the Contractor after one week was able to start injection and30 tons of cement was placed. A successful excavation through the zone wasfinalized before the added pump installations as instructed by the Owner, wereoperational.

The Osane access tunnel and water tunnel (75 m2) were both excavated on adecline. Frequent ground water problems were encountered. A summary after2300 m of tunnel excavation shows the following:

• Total quantity of cement injected was 1100 tons

• Added cost due to ground water problems was USD 10 m

• A maximum of 175 tons were injected from one face position

• The typical ground water static head of 15 bar, corresponded well with theoverburden

7.9.3 Holen Hydropower Scheme (South central Norway)

The access tunnel Øyestøl was excavated on a decline and in the water tunnelthe typical ground water static head varied between 20 and 50 bar. Typicalproblems encountered were bent and damaged packers, sand and waterpunching into the drilling machines, back flow of cement through cracks in theface etc. In two cases failures occurred behind the face, in pre grouted areaspassed by the face.

A grout failure and water inrush behind the face under such high static head isextremely difficult to stop, but not impossible. In the above mentioned cases,the open joints filled by grout material were typically 100 mm wide, with substantiallocal variation. The blow outs occurred at wide spots, where the depth of cementfilling was insufficient to sustain the water pressure.

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Steel pipes of diameter 75 to 150 mm were driven into the inrush channel(s), asmany as possible. Additionally, relief holes were drilled from the sound side rockinto the water bearing zone. When a sufficient pressure relief was established,valves were fitted to the steel pipes and anchored to the rock by rock bolts. Thewhole pipe and valve assembly was then encased in reinforced shotcrete, alsoanchored into the rock. After necessary hardening, packers were used to closethe relief holes and the valves on the steel pipes were closed. Normally, thisexposed serious inflows around the pipes and the concrete plug that had to besealed by grouting and additional shotcrete, while all valves and packers wereopen. Still, the start of injection had to utilize saw cuttings, concrete with particlesize up to 10 mm and stiff mortar with anti-washout admixture. As soon as theback flows were under control, a stiff cement mortar with a low w/c-ratio ofabout 0.5 was used for injection.

A prerequisite for a successful sealing of such blow outs, was stiff mortar, loww/c-ratio, 50 bar injection pump over pressure capacity, sufficient quantity injectedand at least 24 h hardening time before any disturbance could be allowed (likeremoving packers or pipes and valves).

7.10 Experience rules in summary

High ground water static head, high ground water yield, excavation on downslope and other possible problem enhancing features, requires that the followingset of principles should be applied:

• Probe drilling ahead of the face on a routine basis must be executed. Theamount of pre grouting shall be balanced against the cost of pumpinstallation and operation. Pre grouting and pumping shall both be used(these measures are not alternatives).

• The reserve pump capacity must be at least 100% more than the maximumexpected water inrush.

• A backup diesel generator is often required.

• It is a requirement that the grouting equipment has sufficient capacity regardingflow and pressure and the ability to pump particle size above 5 mm.

• Post grouting is difficult and time consuming and may become impossible.

• Pre grouting, on the other hand, is simple and efficient, provided that atight face area is maintained. A 5 to 10 m buffer is recommended.

• High static head requires care and special measures. Do not allow highpressure water too close to the face, particularly if in poor ground.

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• Using the consumption of cement as the main pay item is equal to invitingproblems. Even at high consumption of cement, the cost of cement is onlyabout 5% of the total time related cost and injection cost. It is obvious thatsuch a relatively small and highly variable cost factor should not be themain basis for payment.

• Depending on conditions, the added cost of pumping, probe drilling andpre grouting may be in the range of 50 to 100% of the excavation cost.

• Finally: Keep the face area watertight and never blast the next round if indoubt.

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8. EQUIPMENT FOR CEMENT INJECTION

There are many ways of executing injection with cement and because of therelatively low cost of the material sometimes it is believed that the equipmentside can be improvised with little negative consequence. This would be a seriousmisunderstanding and the result of such an approach to cement injection wouldbe an overall cost increase and poor effectiveness.

There are many specialist manufacturers producing high quality equipment forcement grouting, far too many to be presented here and it is not the purpose ofthis publication to grade them or give any particular recommendations. Still, it isstrongly recommended to select a complete set of equipment from one of thesespecialist companies before starting any sort of grouting operation underground.Especially if the requirements call for the use of micro cement it would be a totalwaste of a more expensive and efficient material, not to use modern customdesigned dedicated equipment.

Companies like Atlas Copco Craelius, Haeny, ChemGrout, Montanbuero andColcrete are all good options when seeking an equipment manufacturer, but asmentioned, there are many others.

8.1 Mixing equipment

The whole process starts by mixing the dry cement with water and often withother components of the mix, like chemical admixtures, sometimes Bentonite,sand or other materials. The crucial point here is to get all the cement particlesproperly wetted by water.

This may seem a simple task, but if you try to do it manually with just a smallcement quantity you will see that it is not so straightforward. Good mixingequipment is absolutely necessary to achieve good results. Mixing equipmentwill fall in two main categories:

1. Mixing by agitation

2. Mixing by high shear action

Figure 8.1 Paddle mixer [8.1]

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The first method is typically some sort of paddle mixer as illustrated in Figure8.1. The agitation creates turbulence in the mix and after some time the mix willappear to be uniform. The drawback with this method is that it will not fully breakup dry lumps of cement (in reality consisting of many individual cement particles).The surface tension of water tends to preserve such lumps and this createsgrout segregation, blocking of small openings and build-up in bends, valves andother parts of the equipment.

The high shear mixers are normally termed colloidal mixers. These units typicallyconsist of a tank with a high speed circulation pump. Water and cement is drawnfrom the bottom of the tank, running through the high speed impeller of thepump and returned on top of the tank. A good colloidal mixer will have an impellerspeed of 1500 to 2000 rpm and the shear action is strong enough to break upall lumps to properly wet individual single cement particles.

The high shear is created either by the tight tolerance between the impeller andthe housing or by intense turbulence (see Figure 8.2 and 8.3 respectively).Typically the whole tank volume should be fully circulated at a rate of aboutthree times per minute. It should be noted that the principle shown in Figure 8.3is best suited if there is a need of adding sand or other coarse materials to thegrout, due to lower wear cost.

Figure 8.2 Tight tolerance [8.1] Figure 8.3 Turbulence [8.1]

The difference in mixing efficiency between colloidal mixers and other types iseasy to demonstrate by simply comparing the grout behaviour of equal mixdesigns and mixing times after mixing with the two types of mixers. Tall glasscylinders filled with grout will demonstrate a substantial difference in bleeding.Pouring grout from a paddle mixer onto a low plate and allowing it to harden willshow distinct layering when breaking up the cement cake. The same test givesa uniform layer using the colloidal mixer.

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When injecting a cement grout it is mostly executed against ground water. Paddlemixers will create a grout that has a strong tendency to be diluted and washedout. With a colloidal mixer the grout is much more stable and will tend to displacethe water rather than mixing with it. By simply lowering a spoon of grout intowater and turning it upside down (to allow the grout to fall through the water),the difference is well demonstrated. The paddle mixer grout will totally dissolveand segregate right out of the spoon and all the water becomes a cement cloud.With the other grout you can observe how the grout falls like a lump with muchless cement cloud created.

Be aware that the high energy used in a colloidal mixer will raise the temperatureof the grout. This is not a problem in normal operation carried out as specified,but if too long a mixing time is used the batch may be unusable and could set inthe mixer. Micro cement of the fast setting type could be very sensitive to thiseffect and the mixing procedure must be well controlled. Typically, one batch ofgrout is created in about four minutes. The circulation pump is then used tosend the prepared batch to an agitated holding tank, from which the injectionpump is drawing grout. Therefore, even though the mixing is batch-wise, thepump may still operate continuously.

Figure 8.4 Typical colloidal mixer (photo ChemGrout)

Colloidal mixers are made in a variety of sizes and there must be a balancebetween the maximum pump output and the maximum capacity of the mixer.The equipment manufacturers will normally offer well balanced equipment setsto suit the needs of a customer.

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It is recommended to only use weight batching of the grout components, due tothe much better accuracy. Liquid components may of course be added volumetric,provided reliable measuring devices are employed.

8.2 Grout pumps

To be able to execute well controlled high pressure grouting in rock it is necessaryto have a suitable injection pump. Even though progressive cavity pumps havebeen used for decades in numerous rock grouting projects (primarily damfoundations and other above ground projects) it is still clear that this pump typetoday is unsuitable for most under ground tasks. The reasons are many, butmost important is the limited maximum grout pressure, the high wear cost onrotor and stator and the unpractical pressure control system provided by a returnline to the hopper with grout flow control valve.

Today’s preference in underground grouting projects is the piston plunger pumpwith a hydraulic drive system. Such pumps will normally work on a single groutingline. This pumping system requires and allows independent grout pressure andgrout flow control without any valves or mechanical control parts in contact withthe grout. The operating reliability and the control accuracy are also good. Theplunger pumps furthermore have the advantage of low wear even with abrasivegrouts and they operate reliably at very low output. A high pressure may bemaintained over time at marginal or no output.

Figure 8.5 Pressure pulsation by piston or plunger pumps [8.1]

There is full agreement that it is necessary to require a tight pressure control toavoid exceeding the set allowed maximum. Pressure peaks above the set levelat start of a piston stroke (because of inertia of the grout column) is unfavourableand it is not a property of modern equipment. Pressure above the limit maycause damage to nearby structures or cause unwanted fracturing of the ground.

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Regarding the effects of the pressure pulsation that is normal for piston andplunger pumps, there is not the same general agreement (see Figure 8.5).Some say that a constant pressure and flow is best, others that the pressuredrop between pump strokes is actually an advantage. Practical experiencesupports the idea that the pressure drops actually improve grout penetration[8.1]. The reason for this seems to be the re-arrangement of particles that areabout to bridge and block a narrow joint (causing pressure filtration and fullblockage) when the pressure suddenly drops. When the pressure increasesagain, the same particles may again move some distance without bridging.

8.3 Complete systems

Most manufacturers of grouting equipment will today offer complete systemswith all elements included (mixer, agitator and pump), frequently including aPLC control of batching with the mix design ratios pre-stored in memory. Forsuch systems to operate properly there must also be integrated componentweighing and accurate measuring devices for water and admixtures.

The layout of such systems can vary quite a lot and the size may range fromsmall compact units to be put on a small truck or trailer, to larger units that willneed a heavy dump truck chassis. The larger units may also have hydraulicworking platform to allow access to packer placements in the roof of the tunnel,which can be more than 10 m up in larger road tunnels.

One example of an assembled system is shown in Figure 8.6.

Figure 8.6 Complete system (mixer, agitator and pump) (photo Atlas Copco)

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A real high-output equipment system for pre-excavation grouting in larger tunnelshas been assembled by general contractor AF Spesialprosjekt AS/SRG of Oslo,Norway. See Figure 8.7. The equipment unit contains 2 colloidal mixers, 4 agitatorvessels and 4 hydraulic pumps, each pump capable of delivering 60 l/min at100 bar grout pressure. The whole system has been built into a container, whichis put on a normal heavy-duty road truck.

Figure 8.7 Container-mounted 4-pump grouting system (AF Spesialprosjekt AS/SRG)

8.4 Recording of grouting data

The traditional way of recording data has been manual recording of the maininjection parameters by writing them into pre-printed forms. Of course groutingpressure, cement quantity, type of mix into which hole along with general datalike location, date and time are noted this way. Actually, this part of the workmay require an extra person just for the record keeping, especially if theprocedures are complicated and many different parameters have to be accuratelyrecorded.

Since time is money at the tunnel face it often happens that more than one borehole gets injected at a time. The manual recording task then quickly becomesimpossible.

Today there is a number of alternatives available to improve the data recordingand to reduce the workload for the operators. The simplest device is a pressuretransducer and an inductive flow meter coupled into the grouting line, writingthe data to a chart recorder. The printed data sheet can be collected when thehole is finished the unit may be reset and then the next hole can be started.Grout quantity may alternatively be recorded based on pump stroke impulsecounting, with quite a reasonable accuracy. See Figure 8.7.

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Figure 8.7 Grout recorder example (photo Atlas Copco)

Regardless how the system is set up and regardless of how many automaticrecording devices are used it is important that a good visual control of injectionpressure is available at all times. A good manometer with a simple and clearscale must be installed in a place where it is easily observed. See Figure 8.8.

Figure 8.8 A good easy to read manometer is important

More advanced versions will send the data to an electronic data logger, but thisis just a different way of recording the same data. However, when using dataprocessing (a PC), this adds the opportunity to actively control the processfrom the PC. The PC may be input with control parameters like maximum allowedinjection pressure, maximum and minimum flow rate and maximum quantityinjected per hole. The PC will then record the process automatically, but alsostop the pump when any of the stop criteria has been reached. When injectingon several holes simultaneously (with one pump per line) this equipment is agreat help in keeping things under control and getting accurate recordings,without adding more staff. At a tunnel face with extensive grouting it will quicklypay for itself and increase the work quality and effectiveness.

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9. OUTLINE METHOD STATEMENT FOR PRE-GROUTING IN ROCK

This Method Statement is written specifically for the use of Rheocem®microcement or for microcement with similar properties. The most importantfeatures that must be satisfied for this Method Statement to be applicable are:

• Stable grout with less than 5% bleeding (normally zero), thixotropicbehaviour, Marsh cone viscosity of less than 35 s, quick setting grout andgood pressure stability (low filtration coefficient).

Soil injection is not considered and primarily this statement is intended forbasically competent rocks from medium hard to hard, including the normalfrequencies of weak zones and particularly jointed and crushed zones. Typically,such tunnelling is carried out by drill and blast and this is the excavation methodconsidered in this document. The same principles will be applicable also in ahard rock TBM tunnel and this Method Statement can be developed and modifiedalso to cover this excavation method, but this is not included here.

In a practical case with very strict water ingress limitations it would be beneficialto combine the use of Rheocem® microcement and the colloidal silica MEYCO®MP 320. For control of backflow problems and in post-grouting situations, therange of one and two component PU products of the MEYCO® MP 355-seriescould also be used as a supplement.

9.1 Drilling

9.1.1 General

Drilling of probe holes and grouting holes is done with multi-boom drilling jumbothat is primarily used for the blasting holes. Typical drill bit diameter is 51 mm or64 mm with rods and rod couplers fitting the drill bit chosen. During drilling, thepenetration rate, occurrence of weakness zones, water (or loss of flushing water)and other selected parameters shall be observed and recorded in a preparedformat by the drilling supervisor or operator.

Together with the measured water in-leakage from the drilled holes, this recordforms the basis for the action to be taken, e.g. choice between injection/noinjection and if injection how many additional holes, what length etc. See Figure9.1, the decision flowchart at the end of this Chapter.

9.1.2 Flushing of boreholes for injection

The first requirement is a good water flushing during drilling of the hole. Thewater pressure used shall be at the maximum specified by the drilling equipmentmanufacturer and shall be ensured by a special pressure booster on the drillingjumbo.

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Further cleaning of the injection holes must be described as either a procedurecombining water and compressed air or by high pressure water cleaning like itis described in Chapter 6 and Figure 6.8.

Flushing by water and compressed air should be done using a stiff plastic hoseusing water at 10 bar pressure, combined with some compressed air. Push thehose to the bottom of the hole, open up for water and air and withdraw the hosewhile flushing is on. If there are zones in the borehole that may collapse ifsoaked in water, or if the in-leakage from the hole is larger than 10 l/min theflushing should be omitted.

Flushing of boreholes for grouting shall be done as specified as a routine matterand any necessary deviations shall be decided and recorded by the supervisor,based on the borehole records.

9.1.3 Length of boreholes

Probe holes are normally less than 30 m long. The length specified may beinfluenced by the chosen borehole diameter, as the deviation is substantiallylarger for the 51 mm diameter equipment than for 64 mm. Normally, a balancebetween drilling effort, drilling accuracy and risk of getting stuck, injectionefficiency and efficient tunnelling progress is aimed at. If four to five rounds canbe blasted between probe drilling (and possibly injection rounds), this is thetypical choice.

9.1.4 Number of holes, hole direction

Generally, holes are drilled from close to the tunnel sidewall contour throughthe tunnel face, using an angle between 5° and 8° in a pattern creating a conewith the top cut off. There are situations with very dominating joint orientations,that may call for an adapted preferential borehole direction, but mostly this isnot necessary or beneficial.

Probeholes are drilled to reduce the risk and to detect areas where pre-injectionshould be carried out. The probability of problem detection increasesproportionally with the number of holes drilled up to a certain maximum level.Decision on the number of holes must be based on size of the tunnel, riskinvolved (in the tunnel and outside) and the required tightness of the tunnel.This issue shall be covered by the Technical Specification for the project.

When pre-grouting has been decided, the initial number of holes for a first stageinjection will typically produce a borehole spacing at the face of 1.5 m to 3.0 m.Subsequent stages (if necessary) will be drilled using the split spacing principle.As for probe holes, the spacing of the first stage injection holes shall be specified.

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9.1.5 Placing of packers

The packer is normally placed near to the borehole opening and the hole isinjected over its entire length in one single step. The packer placement depth istypically 1.5 m. However, allowance must be made for a number of differentpossible situations that may require a different packer placement.

High ground water pressure and very poor rock may provoke a face failure andthe appropriate action is to place the packer at larger depth (e.g. 5 m). It happensthat a channel causes water and grout backflow to the face and that the packermust be placed at a depth larger than the depth of intersection between theborehole and this channel. Sometimes the borehole is locally disturbed by weakrock material, local wedge fallout and similar, causing the packer to slide or toleak. Moving it deeper is normally able to solve the problem. In principle, thereis supposed to be an overlap of tight rock (a buffer either from sound rock orgrouted rock from the previous injection round) of say 5 m in front of the face.Normally, the packer placement should be in this zone.

9.2 Injection

9.2.1 General

The decision criteria for pre-injection to be undertaken must be specified. Thisis often based on measured water in-leakage from the probe holes and can bea given number of l/min from a single hole or a maximum sum leakage from allthe probe holes, whichever happens first. Depending on the target maximumwater ingress into the tunnel, the injection could be initiated if a single holeyields more than 4 l/min or if any combination of probe holes yield a total ofmore than 15 l/min. The balance between these criteria and the target tunneltightness must be based on experience and local rock conditions, with the optionof feedback from actual results during operation.

Rheocem® 650, 650 SR, 800 and 900 shall be mixed with a w/c-ratio of 1.0using Rheobuild® 2000 PF at a dosage of 1.5% of the cement weight. If thereare reasons for deviation from the above given parameters or materials choice,this shall be specified by the project documents. Decision about local adaptationsmust be made by the injection supervisor, preferably in consultation with theproduct supplier.

9.2.2 Mixing procedure

i) The cement mixer has to be a state of the art colloidal mixer with an impellerspeed of not less than 1500 RPM. The mixer must also be kept in goodmaintenance to work efficiently with microcement.

ii) Add all the water for one batch into the mixer

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iii) Add the corresponding required quantity of cement

iv) Add the Rheobuild® water reducing and dispersing admixture

v) Mix for 3 minutes. Be careful not to exceed the mixing time, since theintensive high shear mixing will generate heat and increase the temperatureof the mix. If the temperature gets too high, the open time of the batchcould be substantially shortened. In addition, don’t cut the mixing timeshort; because microcement is not living up to the term if flocculated clustersare not broken up by the mixer. This requires sufficient mixing time and theuse of Rheobuild® 2000 PF.

vi) Immediately transfer the batch to the agitated holding tank and keep thegrout in slow agitation at all times. Monitor the quantity of grout in theagitator and never start mixing a new batch if the agitator holds a lot ofmaterial and the grout pump is delivering at a slow rate and high pressure.The batches in the agitator should always be kept as fresh as possible.

9.2.3 Use of an accelerator in the grout

There are situations where unexpected backflow can occur through the face oreven further back in the tunnel. Sometimes indications are that a borehole is incontact with extremely large channels with a lot of high pressure water. In bothsituations it can be beneficial to accelerate the cement setting and hardening.In the first case, by stopping the backflow and allowing further injection of theground without loss of material and in the second case, by stopping unnecessaryspread of grout outside of a reasonable distance from the tunnel.

MEYCO® SA 160 is normally used as a shotcrete accelerator, but it works verywell with Rheocem grout in injection works. One advantage is that there is noevident flocculation or thickening at the time of addition and the reaction onlyinfluences the grout after a certain time. The dosage of SA 160 can be adjustedto give the effect necessary (should only be added through a non-return valveat the packer).

Before using MEYCO® SA 160, site tests have to be executed to determine theopen time, setting time and hardening time, with the actual equipment, type ofRheocem and w/c-ratio used on site, site temperature etc. This is very importantto avoid unexpected early setting and risk of premature blocking of holes. Toimprove dosing accuracy and to avoid immediate local reaction when addingthe accelerator, it may be useful to dilute the accelerator by water up to a 50/50ratio (by volume).

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Addition in the mixer (can be done but it is NOT recommended):

i) Follow the mixing procedure for Rheocem as given above in Chapter 2.2.In step v) above when about one minute of the mixing time remains, slowlyadd the decided quantity of MEYCO® SA 160 into the mixer. Proceed asdescribed above. Take a sample from each batch to monitor setting time.

ii) During injection of the accelerated grout, make sure that the speed ofgrout flow through the hose is not dropping too much. If the grouting almoststops (because of no more take at highest pressure), detach the hosefrom the packer and pump back into the agitator to prevent blockage of thehose and pump. It must be decided if the remaining grout in the systemhas to be dumped, diluted by water or pumped into a different hole withhigh leakage (if available).

iii) Always use a T-valve at the packer. If the grout flow becomes very slow, itmay become necessary to open this valve and pump a few strokes ofgrout onto the tunnel floor, to get fresh material into the system and preventclogging of the equipment.

iv) Any longer interruptions of pumping may require a full cleaning of all theequipment and delivery hoses, before continuation of the work.

It should be noted that even if the setting time of an undisturbed sample dropsto 5 or 10 minutes, the agitated material will still show an open time of 20 to 30minutes (temperature dependent), so the key to a successful use of this techniqueis: keep the grout moving.

Addition at the packer:

i) Addition at the packer has to be done by a separate pump and deliveryhose, connected to a non-return valve coupled into the grout line at thepacker head. This non-return valve has been described in Chapter 4 andis illustrated in Figure 4.4.

ii) The pump for MEYCO® SA 160 can be a Wagner diaphragm pump forspray painting, giving a maximum pressure (300 bar) substantially higherthan the grout injection pressure. The output is adjustable and because ofthe high pressure, will not be influenced by the pressure in the grout line.

iii) Based on pre-testing of dosage and calibration of the pump, dosage ofMEYCO® SA 160 can be started at any time, can be increased in stepsuntil the targeted effect has been achieved and can be closed at any stage,keeping the injection line open.

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9.2.4 Injection pressure

As is always the case, the maximum injection pressure has to be evaluated ona running basis and especially it has to be checked against local conditions inthe tunnel. Very poor rock conditions in the face area, high hydrostatic waterpressure and existing backflow, will be indicators that maximum pressure mustbe limited, even if the rock cover is hundreds of meters.

However, in pre-injection the maximum allowed pressure should be used fromthe beginning of injection (if the pump can deliver sufficient output to reach thispressure) until alternatively:

i) No more grout is accepted by the ground at maximum allowed pumpingpressure, or

ii) The maximum specified grout quantity for the hole has been reached,regardless of pressure used

whichever happens first. With this approach the quantity of grout that can beplaced will be executed in the shortest possible time and by working at thehighest possible/allowed pressure from the start of the process, the spread ofgrout into the smaller cracks and joints will be optimized.

The permitted maximum grouting pressure should be at least 50 bar above thestatic ground water head, unless there are special reasons identified requiringa lower maximum pressure. In pressure sensitive situations it must also berecognised that the danger of causing damage by lifting, splitting or otherdeformations, is rather linked to the product of pressure and quantity, than topressure alone. A high pressure exerted on the borehole alone (quantity onlysufficient to fill the borehole) will not cause “damage” anywhere other than thelocal hydraulic fracturing of some dm around the borehole itself.

9.2.5 Injection procedure

i) Start injection of the lowest hole in the face and work upwards, alternativelythe holes with the largest water inflow to the tunnel should be grouted first.

ii) A hole is finished when the maximum allowed pump pressure is not givingmore than 2 l/min grout flow during a 2 minutes period, or when the specifiedmaximum grout quantity per hole has been injected.

iii) If backflow of grout and water into the tunnel is detected, this should beminimised by reducing the pump output and accelerator MEYCO® SA160should be used to create a blockage of the backflow. A decision must betaken which method to use (addition in the mixer or by separate pump).

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iv) If during the injection process two or more holes become inter-connectedas demonstrated by grout backflow through the holes, close the packers inthose connected holes and continue grouting on the current hole. Themaximum amount before stop shall be multiplied by the number ofconnected holes. If the maximum pressure is reached before the maximumquantity, then the connected holes shall be injected as well, if they takeany grout.

9.2.6 Injection Records

Records of the injection data have to be taken as a matter of routine. Part of thismay be automatic by computerised recording if the system is suitably equipped.Otherwise, there must be well prepared forms to be used in the tunnel duringwork progress. It must also be well defined who is responsible for the recordkeeping.

As a minimum the following information must be recorded:

i) General data like tunnel location, date, time and shift, person who doesthe recording, identification and location of all holes, measured water flowfrom the holes.

ii) Per hole: packer placement location, length of hole, grout mix design,pressure at start and end, time at start and end, flow rate development,total grout quantity, any leakage (backflow) and any connections to otherholes

9.3 Setting of grout, time until next activity

Rheocem is specifically developed to behave as a thixotropic grout and to giveinitial set a short time after the end of injection. The purpose is to allow work toproceed without breaks. At moderate ground water head (say less than 15 bar)and if water bearing channels are limited in size (say maximum thickness lessthan 10 mm), then this should be possible without risk.

When the pressure increases and especially if also the channel dimensionsincrease at the same time, the risk of grout material failure and wash out willincrease. It is not possible to give general rules about how to evaluate this,other than that the aspects of consequences of a failure, time allowed for settingand the water pressure and channel size in the ground, have to be considered.

If accelerator has been used to shorten setting time, be aware that this will be agood help for the actually accelerated grout, but experience tells that only a partof the grout in one injection stage is normally accelerated. Caution must beused if the consequences of failure are serious.

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If the next planned activity is drilling of boreholes for control of injection result,or for a next round of grout holes, always start drilling in the area where theprevious injection was first completed (giving the maximum setting time).

9.4 Drilling of control holes

The efficiency of a stage of injection must be controlled by new boreholes.These holes will be evaluated using the same decision criteria as used for theprobe holes in regard of injection or no injection. Control holes shall be drilledon both sides of all holes that yielded water flow above the injection criteria. Ifthe project requires the use of an acrylate grout the decision criteria for a secondstage (or subsequent stages) must tell when to use such grout.

Holes that are tight and all holes, if no injection is necessary, shall be filled bystable cement grout. This can be done by rock bolting mortar, if preferred, toavoid starting up and cleaning all the injection equipment just for backfilling ofthe holes.

9.5 Measuring of water ingress in excavated parts of the tunnel

Control of achieved tightness in the tunnel behind the face is the only way ofconfirming the result of carried out injection. After a certain length of tunnelexcavation, the average water flow out of the tunnel must be checked. By installingsealed dams in the floor, with V-shape overflow, the in-leakage over definedtunnel sections can be measured. To get accurate readings, it will normally benecessary to measure at the end of a weekend, to avoid disturbance from otheractivities that use water in the excavation.

If the required in-leakage rate has been exceeded, post grouting of the remainingleakage spots must be carried out, starting with the largest ones. Also, anevaluation of the pre grouting procedure and criteria must be conducted, todecide if an adjustment is necessary.

9.6 Decision-making Flowchart, example criteria (Figure 9.1)

Step I: Probing ahead. Standard number of holes is two, in clock positions 12and 6. In high risk areas, use four holes, in positions 6-9-12 and 3. Maximumdrilling length per hole, 30 m. Use percussion drilling with water flushing.Recommended drill bit: 51 mm diameter. Start holes at tunnel contour, angleout 5 to 8°. Overlap with end of last drilling is minimum 5 m.

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Recordings to be made during probe hole drilling:

• indications of any weak zones, higher drilling rates, voids.

• loss of drilling water.

• depth of detectable water in-leakage.

• after drilling of a hole, drill string removed: initial water in-leakage rate inl/min.

Apply maximum flushing with water and compressed air, when pulling out thedrill string at the end of drilling, for proper cleaning of the hole.

Grouting Criteria, A: Injection shall be carried out, if any of the following criteriaare met:

• Initial in-leakage from any single hole > 3 l/min.

• Total initial in-leakage from all holes > 6 l/min.

• Loss of more than 50% of the flushing water (approximate), in any singlehole

Figure 9.1 Flowchart of decisions regarding probe drilling and injection

Distance Criteria, B: If all, or a major part of the recorded in-leakage or loss offlushing water locations occur deeper than 15 m into the holes, then the faceshall be advanced to a minimum distance of 5 m from these features.

Step II: Grout filling of probe holes. Place a packer minimum 2 m into the probeholes and inject grout for the purpose of filling the hole. Stop if a pressure of 20bar is reached, or if the pumped quantity reaches 300 kg. Holes can alternativelybe filled by anchoring mortar through an open plastic hose from the bottom up.

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Step III: Advance the face. Advance the face until a minimum of 5 m probingoverlap is reached. Execute next stage of probe drilling.

Step IV: Add bore holes for grouting. Add bore holes until total number equals 8.Positions 6-9-12-3 and 7:30-4:30 shall be covered first. The last two holes shallbe added in the area of most in-leakage or flushing water loss.

Step V: Advance the face. Advance the face until a minimum distance of 5 mfrom the features that initiated the grouting decision.

Step VI: Add bore holes for grouting. Add bore holes until total number equals 8.Positions 6-9-12-3 and 7:30-4:30 shall be covered first. The last two holes shallbe added in the area of most in-leakage or flushing water loss. The length of theadded holes shall be adjusted to end at the same chainage as the previousholes.

Step VII: Pressure Grouting. By packer placement at minimum 1.5 m depth,start grouting in the lower part and work upwards. All holes shall be grouted.Stop the grouting of a hole if the pressure reaches 50 bar, or if the pumpedcement quantity reaches 1500 kg.

Step VIII: Control holes. Drill minimum 4 control holes (after a careful evaluationof required minimum time for cement hydration), increased to 8 holes if highgrout takes occurred in most of the previously grouted holes. Location of controlholes shall be adjusted, based on distribution of grout takes and location ofrecorded features.

Apply the Grouting Criteria A on the control holes, for decision on the next step.

Step IX: Add holes. If necessary, add boreholes to a minimum number of 8holes available for grouting. Location of holes shall be adapted to availableinformation on features in the ground, in-leakage locations and distribution ofgrout takes.

Step X: Grout filling of control holes. Place a packer minimum 2 m into thecontrol holes and inject grout for the purpose of filling the hole. Stop if a pressureof 20 bar is reached, or if the pumped quantity reaches 300 kg. Holes canalternatively be filled by bolting mortar through an open plastic hose from thebottom up.

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10. EXAMPLES OF RESULTS ACHIEVED

10.1 General

The term waterproofing is sometimes used when considering sealing of rock bygrouting. A more correct term would be ground water control or conductivitycontrol. The reason for this is that a 100% drip free and watertight tunnel cannotbe guaranteed by pre-injection and post-injection methods, even with the mostelaborate procedures.

However, for a number of purposes it is possible to reach what is required andin many cases with less effort and cost than most engineers would assume inadvance.

Generally speaking it is possible with reasonable means using pre-injection toreduce the water ingress into a tunnel to a few percent of what it would havebeen without injection. However, be aware that the additional cost of improvingwater ingress reduction from 90 to 95% can be higher than sealing off the first90%.

10.2 What is achievable?

This question is probably wrong, because almost anything is possible if theresources are unlimited. More relevant is it may be to use project examples witha focus on the local situation, with targeted and achieved results.

How much relative and absolute improvement of the ground water ingresssituation that can be achieved will depend on the hydrogeological situation i.e.primarily the character of jointing and the number of joint sets.

The improvement in the ground water situation may be limited to around twoorders of magnitude if the rock mass surrounding the tunnel is highly fractured.This is what can be regarded as a ’worst case scenario.’ The sedimentary rocksin Oslo are of this type, with extensive jointing along 3 joint sets with spacing inthe 10 mm and 100 mm scale. Under such conditions and based on a largevolume of water pressure testing of boreholes (before grouting situation) andback analysis of water ingress into pre-grouted, executed tunnels (after groutingsituation), the general rock permeability without grouting was determined as k= 1•10-7 m/s and the improvement achievable by pre-injection by cement andchemicals was given as end result k = 2.5•10-9 m/s [10.1].

However, in hard rock conditions with granites, granitic gneisses and similarstiff and brittle rocks, there is no real limit to the relative improvement obtainableby pre-injection. There are a large number of examples showing water featuresahead of the tunnel face that would certainly drown the tunnel if left untreated.

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The same features are subsequently tunnelled through without major problems,after pre-injection. (There are also examples of decisions or ’gambles’ to goahead excavating without pre-injection in spite of serious indications that thereis a lot of water ahead, causing a flooding situation). The main consideration isto keep a tight bulkhead of sealed rock between the water feature and thetunnel face, until all the rock ahead of the ongoing excavation has been properlyinjected (see Chapter 7).

To take one example, the Bjorøy sub-sea road tunnel got into extremely difficultground water conditions, with several hundred metres of tunnel producing fullwater flows from all probe holes at up to 7 bar pressure (70 m below sea level).Frequently, the tunnel crossed areas with water-filled joints that were typicallymore than 100 mm wide. After excavating through one injected section, anoriginally 400 mm wide open joint was recorded as being completely filled bymicro cement [10.2]. This statement can be found on page 252, Item 4.1 a.

Without pre-injection of a discontinuity of this size, the tunnelling would simplyhave been impossible. The paper furthermore states on page 250, Item 3:”When encountering the zone with exploratory drilling ahead of the tunnel faceat a distance of 8 – 10 m, several cubic meters of sand and silt were flushed intothe tunnel through the drillholes (51 mm diameter) together with water leakagesof about 200 l per minute. Hence, the untreated condition of the soil is assumedto have had a behaviour like running ground”.

With pre-injection of cement, microcement and acrylate grout the normallyrequired level of water ingress for such tunnels was actually reached.A satisfactory ground stability to allow very careful excavation through the zone,was also provided. See more details later in this Chapter.

10.3 Comparing shallow and deep tunnels

10.3.1 Some shallow hard rock tunnels in Sweden

Figure 10.1 Nomograph indicating tightness target complexity

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Stille [10.3] discusses the development from unstable cement grouts using OPCto stable and low viscosity grouts with micro cement. To illustrate what it ispossible to achieve in terms of leakage reduction by cement injection, the paperpresents a line nomograph as presented in Figure 10.1. Use of the nomographby starting at an assumed ground water ingress of 1500 l/min per 1000 m anddrawing a line through an assumed target of 200 l/min per 1000 m after injection,indicates that this is a medium level complexity. This is a reduction of wateringress by 87%.

It is important to note that the difficulty of achieving a certain specified result interms of water ingress is far more dependent upon the required tightness level(50 – 100 or 200 l/min per 1000 m) than by the level of water ingress before anyinjection of the rock takes place. Even if the untreated ground would yield 15000l/min per 1000 m this would not reduce the probability of reaching e.g. 200 l/minper 1000 m. Under hard rock conditions, reduction of water ingress by twoorders of magnitude is frequently quite easy to reach.

Erikson and Palmqvist [10.4] report on specified water ingress limits of between0.5 and 2.5 l/min per 100 m, depending on local risk level in the project, asshown in figure 2 on page 161 of their paper. The measured water ingress afterthe end of the construction period showed results from 0.85 to 1.1 l/min per 100 m,as given in figure 7 on page 172. It is noteworthy that this result was reachedwith cementitious grouts only.

The English translation of the summary of the paper in reference [10.5] byHässler and Forhaug reads as follows:

“A good result can be achieved with close to no water drips from the roof inmica shist, even with relatively few curtain holes, fast grouting cycle and avoidingtime consuming execution controls. Finely jointed mica shist with clay-filledjoints can be well grouted with stable grouts based on cement. An even curtainwith small volumes in many holes can be better than an uneven curtain withlarge volumes in few holes. Extremely high pressure, especially in the first phaseof the grouting, can improve the result. Development of grouting methods duringthe project is good for the result”.

Sundin and Karlsson [10.6] report about a tunnel that is 3.7 km long and has adiameter of 3.5 m. The rock types are granites and granitic gneiss. Probe drillingahead of the face was mostly carried out by drilling 8 holes, each with a lengthof 25 m, starting 8 m behind the face. The required maximum water ingress was2 l/min per 100 m and pre-injection was successfully carried out where necessary.

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Hahn [10.7] describes a tunnel which is 7.6 km long and has a diameter of3.5 m. The rock types are granites and granitic gneiss with some amphibolite.The required maximum water ingress was 5 l/min per 100 m and pre-injectionwas carried out where necessary. A substantial part of the total water ingressoriginated from within 18% of the total tunnel length. About 15% of the probehole length gave water loss measurements equal to or larger than 1.0 Lugeon(about 2 • 10-7 m/s). About 5% of the length showed more than 10 Lugeon(about 2 • 10-6 m/s).

On behalf of the Södra Länken highway tunnel project in Stockholm, the RoyalTechnical University of Stockholm sent out a materials request to suppliers dated12 May 1999 (Mr. T. Dalmalm). Some interesting information is given in therequest in terms of the tightness requirements that were expected using injection:

“Maximum allowed water ingress of 1 – 3 l/min per 100 mBased on a number of tunnelling projects in the Stockholm granitic rocks:75% of the rock mass has permeability < 1 Lugeon (k = 10-7 m/s)20% is more jointed with k > 10-6 m/s5% will cross shear zonesThe cement injection material must satisfy the following:Shear strength > 3 kPa after 2 hoursBleeding maximum 2% after 2 hours”

10.3.2 Some shallow tunnels in the Oslo area

Shallow tunnelling in sedimentary, highly fractured rocks has been extensivelycarried out also in Oslo. The tunnelling in this area, all requiring ground watercontrol by pre-injection, will soon exceed a total of 100 km in length. Someselected references from this area give the following information:

Rock tunnelling in the Oslo area requires pre-injection to avoid surfacesettlements in marine clay deposits. Some early experiences, like theHolmenkollen subway commissioned in 1916, gave settlements of up to 350 mmwithin 200-400 m from the tunnel alignment [10.8]. Page 74, Item 3. As statedon page 74, second column, tunnels driven in Oslo’s sedimentary rocks willgenerally yield in the range of 20 to 40 l/min per 100 m if not injected (thiscorresponds to an overall rock permeability of the order 10-7 m/s). To avoidsurface damage in the most sensitive areas the pre-injection grouting must

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reduce the leakage to 1 to 2 l/min per 100 m. The authors also emphasise thatpost-grouting may be fairly successful in pre-grouted areas, but post-grouting isstated to be no alternative to pre-grouting. The following statement can be foundon page 75, second column:

“Experience shows that fairly good results from post-grouting can only beachieved in pre-grouted areas. Post-grouting is no alternative to pre-grouting”.Furthermore, “experience from recent road tunnels show that water ingressmay be reduced to 2 to 5 l/min per 100 m by the use of cement pre-injection intunnels of 60 to 100 m2 cross section”.

10.3.3 Deep situated tunnels

Since 1979, 17 sub-sea road tunnels have been constructed in Norway. Most ofthem are located in hard rock, with maximum depths of between 56 to 260 mbelow sea level and all of them were systematically probe-drilled and pre-injectedwhere necessary.

With cross sections in the range of 43 m2 to 68 m2, the water ingress aftercommissioning varies from 10 to 45 l/min per 100 m. These results have beenachieved with cement grouting alone and with a typical target tightness of about30 l/min per 100 m. In this sense they are not illustrating what is ultimatelyachievable by injection techniques, but illustrate well what can be achieved byquite reasonable measures.

10.4 Sedrun Access tunnel, Alp Transit Project, Switzerland

The 1000 m long access tunnel to the vertical shaft (800 m down to the maintunnels level) hit a small sub-vertical shear zone that yielded about 200 l/min. at10 bar. This concentrated ingress was not pre-injected and because of thenuisance of the flowing water, an attempt was made to reduce the ingress bypost-injection.

Since this was a concentrated ingress with good rock on both sides of the aboutone meter zone of disturbance, it was considered possible to succeed and anacrylate grout was selected for the work. Injection holes were pre-drilled by thecontractor and as it turned out, they were drilled in a way to cross the waterchannels at only one to two meter depth inside the tunnel contour. This wasvery unfavourable because of the risk of back flow to the tunnel.

To counteract this situation the acrylate grout was prepared in batches, allowinga start of gel-formation before start of the injection pump (an ordinary cementpump). In reality what was pumped was gel lumps under formation, albeit stillweak and soft. It turned out that these gel lumps started clogging up the back-flow channels, the ingress gradually reduced and finally, almost blockedcompletely.

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The permanent rest ingress in this area has been measured to between 5 and10 l/min and this was satisfactory to the client (so no additional attempts weremade to further reduce the ingress).

Figure 10.2 Acrylate grout appearing as limited backflow before sealing off

10.5 Bekkestua Road Tunnel, Oslo, Norway

The Bekkestua Tunnel is a short tunnel (705 m long, cross section 68 m2) locatedin a suburb of Oslo in a semi-agricultural area. The initiative to construct thetunnel was taken by the inhabitants of Bekkestua, who wished to get rid of theheavy transit traffic through their town. The tunnel was excavated by the drilland blast method.

Due to the low rock cover (between 2 and 50 m) vibrations had to be reduced toa minimum. Highly jointed limestone with layers of shale was the dominatingrock type. Rock support was carried out by steel fiber reinforced shotcrete,including sprayed-in steel arches in weak zones. Since the tunnel is below theground water level with marine clay sediments resting on the bedrock, measureshad to be taken to prevent drainage and lowering of the pore pressure in thesoil. Surface settlement and damage would otherwise be the result. The limit ofwater ingress into the tunnel was set as maximum 2 l/minute per 100 m oftunnel length.

10.5.1 Practical execution in the Bekkestua Tunnel

Per pre-injection station a round of 25 holes were drilled with a length of 21 m.Recorded water ingress measured at more than 5 l/min per hole was treatedwith normal Portland cement and 2% of Rheobuild 1000 admixture for waterreduction. Maximum cement quantity per hole was set at 4000 kg and maximuminjection pressure at 30 bar.

For measured water ingress less than 5 l/min per hole, injection was carried outwith Rheocem microcement, with 3% of Rheobuild 1000 as water reducing anddispersing agent. Maximum microcement quantity per hole was 2000 kg atmaximum injection pressure of 30 bar.

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The resulting measured total water ingress to the tunnel at the end of theexcavation period was 0.7 l/min and 100 m tunnel length. The largest leakage of1.7 l/min and 100 m tunnel was recorded in a section where only OPC hadbeen used (no microcement).

The project consumed in total 583 tons of Rheocem 650, 40 tons of Rheocem900 and 556 tons OPC. This was injected through 1440 packer placements anddistributed over 26’000 m of boreholes. The quantities are comparatively high,but this is linked to the very strict ingress limit and the highly jointed sedimentaryrocks. Execution was from August 1993 to March 1994. See also Chapter 11,Figure 11.2 which illustrates the efficiency of using Rheocem microfine cementin regard of both time spent, quantities injected and final result.

10.6 The Bjoroy sub-sea road tunnel

10.6.1 The project

The 1965 m long Bjorøy road tunnel passes under the strait of Vatlestraumennear the city of Bergen in South-western Norway, with a maximum depth of80 m below sea level. General Contractor Selmer ASA was awarded the contractby the Public Road Authority of Hordaland County.

Excavation was commenced in November 1993 on the island side. Breakthroughwas reached in August 1995, when 840 m had been excavated from the islandside and 1125 m from the mainland. The tunnel was opened for public use in1996.

10.6.2 The problem

Extreme conditions were encountered after about 700 m of excavation from theBjorøy side. During routine probe drilling ahead of the face, flowing sand/siltunder 7 bar water head was hit at 8 to 10 m in front of the face. Within a fewminutes, several m³ of water and sand had blown into the tunnel through onesingle 51 mm diameter borehole. The hole yielded water at about 200 l/min.

The main part of the fault system encountered turned out to be a Jurassicformation with competent sandstone, sedimentary breccia and unconsolidatedsand and silt. The thickness of loose sand material varied from a few cm to2.5 m, while the complete zone had a maximum thickness of about 4 m. Thetunnel crossed the zone at 72 m below sea level with a rock cover of about30 m.

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Figure 10.3 The running ground zone

It was quickly agreed that to enter into this type of flowing ground with a tunnelface of about 60 m2 cross section without special measures would be impossible.A number of different technical solutions were considered, including groundfreezing, horizontal jet grouting and different types of spiling and micro pillarinstallation. To be able to use ground consolidation by pressure pre-injection,the key problem was to ensure sufficient penetration into the silty soil to createnecessary water cut-off and sufficient ground stability improvement.

10.6.3 The solution

Extensive ground consolidation activities were undertaken in order to improveground stability allowing an open face excavation and support. Groundconsolidation techniques included cement based compaction and hydrofracturinggrouting, chemical acrylic hydrofracturing and permeation grouting, as well asgravity water drainage from the zone.

Support ahead of the face by spiling and immediate shotcrete support aftershort excavation sequences was utilised. Stability was monitored systematicallyby the use of convergence measurements.

Key elements of the chosen solution was the quick setting, high strength ultrafine micro cement Rheocem® 900 and the acrylate resin MEYCO® MP 301. Theresin provided a permeation capability into the fine sand and silt material andcreated a simultaneous sealing- and strengthening effect in the injected ground.The cement was always used first in several stages, until the necessaryhomogeneity was achieved to allow pressure build up and permeation byMEYCO® MP 301 into the sand lenses.

1460

1470

1480

1490

Direction of excavation

Tectonic breccia, heavily jointed and altered (chlorite, serisite and illite)

Sand and silt with lenses of hard quartz sandstone and broken conglomerate

Biotite gneiss, altered and very poor with high shistosity

Plan view

Core drilling area after break through

Chainage

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The injection was carried out through steel stand-pipes placed around the tunnelcontour. These pipes had also the function of spiling bolts for the subsequentexcavation. Excavation by backhoe, in very short steps and on part face area,was followed immediately by steel fiber reinforced shotcrete.

10 100 1000Grain size in micro meter

SILT SAND

20

40

60

80

100P

erc

en

t pa

ssin

g s

ieve

Grain size of zone materialSamples from core drilling

Figure 10.4 Zone material sieve analysis

10.6.4 Results

The progress through the about 30 m of tunnel length directly influenced by thezone, proceeded slowly and successfully.

Only minimal water seepage was observed and there were no blow-outs oruncontrolled collapse areas. A research program carried out by inspection ofcores drilled through the final concrete lining after the tunnel break through,can be summed up as follows:

• Of the ground inspected, about 50% consisted of compacted silty sand.The compaction effect was sufficient to produce core samples.

• About 25% of the ground produced no core recovery.

• Of the silt and sand material, 10 to 15% had been permeated by the acrylicresin grout MP301.

• Cement lenses had replaced 10 to 15% of the sand/silt ground by splitting,causing compaction of the adjacent silt material.

• Silt permeated by MEYCO® MP 301 showed compressive strengths of 0.36and 0.39 MPa.

For a more complete presentation of the project see [10.2].

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10.7 The Ormen Project (the snake), Stockholm, Sweden

10.7.1 The project

With a frequency of about once per 5 years heavy rainfalls hit the city ofStockholm. This caused problems as the capacity of the network of pipelines forrain and waste water drainage was insufficient. To reduce overflows into thesurrounding rivers and lakes, a tunnel was excavated to serve as a temporarystorage of surplus water until the pressure on the pipelines and the waste watertreatment plants was reduced.

Eight raise-bored shafts lead the rain water from the streets down to this tunnel.Due to its winding form the tunnel got the name “Ormen” (= The snake). TheSnake was constructed at a depth of 40 to 60 m beneath the central parts ofStockholm city in an extremely sensitive area of the old town where many of thehouses are supported on wooden piles. Any lowering of the ground water levelin the vicinity of these buildings would have resulted in serious settlements,rotting of the piles and damage to the buildings.

For this reason the level of maximum permitted ingress of water into the tunnelwas set at 2 l/min per 100 m of tunnel length. This is a very strict requirement,which means a practically dry tunnel.

10.7.2 Tunnel data

The tunnel goes mainly through crystalline gneisses (50%) and granites (40%),interspersed with zones of fractured and weathered rock (10%).

The tunnel diameter is 3.5 m, the total length is 3700 m and it was excavated bya TBM, Atlas Copco Foro 900. Average tunnel production including pre-injectionworks was15 m per day.

In order to meet the project requirements it was decided to use a TBM to eliminatethe risk of vibration damages to overlying structures and also to reduce the riskof extra water ingress caused by blasting cracks in the surrounding rock.

Continuous pre-injection along the tunnel alignment was necessary in order toseal cracks and joints to keep water ingress below the specified limit. Rheocemmicrocement was the chosen grout material for this work.

The Rheocem microcement technology requires the use of a modern colloidalmixer and pretty high pressure during injection (from 30 to 50 bar). The selectedpump from Montanbüro, therefore had a maximum working pressure of100 bar. The equipment worked very reliably throughout the whole project.

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In this case The MBT Underground Construction Team was a consultant to thecontractor (Siab) and produced working guidelines and procedures. MBT UGCInternational was also involved during tendering and further assisted thecontractor in discussions with the client. Both theoretical and practical trainingwas conducted by MBT UGC International.

10.7.3 Some general information

Contractor was Siab AB. Injected quantities were 160’000 kg of Rheocem 650and 40’000 kg of Rheocem 900.

Works period: February 1991 through June 1992.

10.8 Limerick main drainage water tunnel, Ireland

10.8.1 The Project

The tunnel provides a new drainage system for the City of Limerick, linked to astate-of-the-art sewage treatment plant at the downstream end. This eliminatingall untreated discharge to the river and is an important environmentalimprovement.

Murphy Tunnelling was the Contractor for the 2550 m of 2.82 inner diameterEPBM drive. The tunnel is lined by concrete segments and runs at about 15 mdepth. Access for excavation and for sewage connection points are through13 vertical shafts.

10.8.2 The Problem

One of the access shafts down to the main tunnel was located in water bearingfine sand and this soil needed stabilisation to allow safe break-in and break-outof the TBM at the shaft. The soft alluvial deposits, the high water head and theproximity to the river added to the construction problems. Figure zz is illustratingthe general layout of the shaft and tunnel.

Figure 10.5 Break-in area soil stabilisation

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10.8.3 The solution

Fine sands with silt will typically cause injection problems using cement or evenultrafine cement. The penetration may stop prematurely and it is very difficult toachieve a uniform distribution. Many chemical resin products may causeenvironmental hazards in some locations and it was therefore suggested togrout with the MEYCO® MP 320 colloidal silica gel.

The colloidal silica is a nanometric sol, with primary particles of 0.015 micron,coupled with a viscosity of 5 cP (similar to milk). This product can penetrateextremely fine sands and coarse silts.

To facilitate injection, a series of one and two metre long perforated steel pipes,with one-way valves were rammed into the sand through pre-drilled holes in theshaft segment lining. Positions were marked on the outer circumference of thecoming TBM breakthrough. The pipes were sealed in place by quick settingmortar. Refer to Figure 10.6.

Figure 10.6 Injection point through shaft segment lining

The MEYCO® MP 320 was pre-mixed with 20% component B (10% solution oftable salt in water), giving an open time of 30 minutes. This allowed sufficienttime for permeation and the grout could be injected by standard cement groutingequipment.

10.8.4 Results

The mixing of the MEYCO® MP 320 proved extremely simple to undertake, andthe use of standard equipment offered a clear advantage to the tunnel crewcarrying out the grouting operation.

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After removal of the shaft segments to allow the safe breakthrough and breakout,the sand were seen to be effectively treated and stable. The MEYCO® MP 320had solved the problem of ground water control and stability of the soil, butoffered no resistance to the TBM excavation.

10.9 The Kilkenny Main Drainage Tunnel, Ireland

10.9.1 The project

The tunnel is about one meter in diameter and is 200 m long, driven by pipejacking. It passes beneath the town centre with between 5 and 10 m cover tothe surface. The tunnel has been driven through fine to silty saturated sand,causing considerable construction problems.

10.9.2 The problem

The sand was saturated with water, causing it to flow readily once exposedduring excavation. Consequently, the original traditional pipe jacking methodwas abandoned for an Iseki micro-tunneling machine, with jacked steel pipes.There were still considerable problems, like one occasion where the head wasalmost lost to an oversized washout cavity in the ground. Also, settlementproblems occurred due to the close proximity to the foundations of old townbuildings along the route.

Various ground treatment systems had been used to improve the stability of thesand, including PFA, bentonite and cement injection; waterglass injection andalso jet grouting. None of the systems accomplished any improvement to thetunnelling conditions.

10.9.3 The solution

When about 10 m remained to complete the tunnel drive, the sand demonstratedincreased instability. The Iseki machine could therefore not achieve the steeringaccuracy needed to reach the target in the reception chamber constructed frompre-cast concrete rings.

Samples of the sand gave a particle distribution between 0.063 mm and about2 mm, with roughly 95% smaller than 1.0 mm. This indicated soil conditions wellwithin the range of the ground treatment envelope offered by MEYCO MP 301acrylic grout and on the lower border of what is possible with Rheocem 900ultrafine cement. For cost reasons the contractor wished to try the Rheocem900, but ended up using the acrylic grout since this clearly offered the bestsolution.

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Injection pipes were drilled from the concrete segment reception chamber in ahorizontal umbrella fan arrangement. Pipe spacing was approximately 300 mm.Low pressure injection was carried out using a hand pump system and theMEYCO MP 301 acrylic resin was mixed at 1:1 ratio of component A to B.

10.9.4 Results

During excavation of the final 10 m of tunnel the Iseki machine was able tocontinue with improved steering performance. The continuous sand washoutexperienced prior to injection of the acrylic grout was now stopped. Some clearwater was running on the invert of the tunnel whereas before, the invert wasfilled with silt and fine sand. Surface settlement was also well controlled as aresult of the grouting.

10.10 West Process Propane Cavern Project (WPPC), Norway

10.10.1 The project

As an addition to the existing oil and gas facilities at Mongstad, North of Bergenin Norway, a rock cavern has been constructed for storage of liquefied propanegas. The actual rock cavern is 33 m high, 21 m wide and the length is 134 m.The floor of the cavern is located at 83 m below sea level to allow for a groundwater head larger than the gas pressure above the liquid propane.

To allow the storage of propane in liquid form the gas has to be stored at–42º C. The freezing down of the rock surrounding the cavern will be started byair circulation and at the end by filling liquid propane.

Figure 10.7 The propane storage cavern at Mongstad, Norway

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10.10.2 The problem

For such gas storage to work properly and avoid gas leakage to the surroundingsit is crucial to maintain the ground water level during all stages of constructionand operation. This has been achieved by systematic pre-excavation groutingand by the installed water injection system. About 4000 m of guided boreholeshave been drilled for this purpose.

To be able to carry out the freezing-down of the surrounding rock it was also forthis reason necessary to limit the water ingress. Flowing water would otherwisetransport heat into the cavern and at concentrated water ingress spots it couldbecome impossible to stop the water by ice building. It was estimated that theground water ingress would have to be less than 15 l/min measured for thewhole cavern.

10.10.3 The solution

A program was developed for systematic pre-grouting of all excavation stages(top heading, benches and invert). All grouting was done by Rheocem 900Ultrafine cement with Rheobuild 2000PF at 1.5% by weight. The w/c-ratio of thegrout varied from 0.8 to 1.0 by weight.

The pre-grouting work required about 30’000 m of borehole drilling andconsumed 410 t of micro cement.

10.10.4 The result

Measuring of the total ground water ingress after the end of excavation amountedto less than 2.0 l/min with the ground water level being virtually undisturbed bythe project.

Some grouting had to be done in the 450 m of vertical shafts (diameter 2.1 m).The shafts have steel lining with concrete backfill and some water was tricklingin the rock/concrete contact. To stop the water at the bottom part, 400 kg ofMEYCO MP 355 1K polyurethane foam was used. After this blockage was inplace, a total of 500 l of MEYCO MP 320 silica gel was injected. The injectionhoses in the steel/concrete contact were also injected by MP 320.

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11. MBT INJECTION MATERIALS

11.1 The Rheocem range of tunnel grouting cements

Rheocem microcement comes in four different standard types:

1. Rheocem® 650 (Blaine value > 625 m2/kg), a pure Portland cement,particle size:100% < 40 micron98% < 30 micron97% < 20 micron94% < 15 micron77% < 10 micron44% < 5 micron16% < 2 micron

2. Rheocem® 650 SR (Blaine value 625 m2/kg), sulphate resistant type(slower setting)

3. Rheocem® 800 (Blaine value 800 m2/kg), a pure Portland cement, particle size:100% < 40 micron99% < 30 micron99% < 20 micron98% < 15 micron92% < 10 micron58% < 5 micron20% < 2 micron

4. Rheocem® 900 (Blaine value 900 m2/kg), a pure Portland cement, particle size:100% < 40 micron100% < 30 micron99% < 20 micron99% < 15 micron98% < 10 micron73% < 5 micron25% < 2 micron12% < 1 micron

These cements have been specifically adapted for use from a tunnel front, bygiving a very short setting time of about two hours. In the laboratory a 1:1 water/cement ratio (by weight) at 20 °C will give initial set (measured by Vicat needle)of 60 to 120 minutes and final set (defined as 1 mm penetration by the Vicatneedle) of 120 to 150 minutes. Under most practical conditions, the open timein the equipment is still one hour as long as the grout is agitated. (Be aware thatthe SR versions are slower, showing final set in about 6 hours). The importance

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of short setting time has been covered in Chapter 2, Handling of rock conductivitycontrast and is primarily linked to economy. Also the strength development andfinal strength is superior to most other microcements. When calculating thecontractor’s cost per meter of tunnelling, the time related cost items frequentlyamount to more than 60% while cement (when using OPC) cost regularly lessthan 5%. This is why it is possible to use a cement costing about three times asmuch per kilo and still save money. The work proceeds in less time.

Max 6 bar

Water saturated sand

w/c-ratio = 1.0Pump

Rheocem 900

Best

Poorest

Figure 11.1 Pressure stability and permeation dependent on the admixture

The second most important parameter common to all the four types is pressurestability, or the low filtration coefficient. Here it must be emphasised that thisproperty is only maintained when using the prescribed low w/c-ratio of 1.0 andby the use of Rheobuild® 2000 PF at about 1.5 to 2.0% of the cement weight.This particular admixture gives the combined effect of low viscosity (Marshcone flow time of 32 seconds), no segregation and the low filtration coefficient.Thus, penetration is excellent without loss of stability. The practical results in anumber of tunnels have demonstrated superior results when other cementshave also been tested.

The importance of the right admixture has been demonstrated by test injectionin sand-filled plexiglass tubes. Using Rheocem® 900, w/c-ratio 1.0 and onlyvarying the admixture (28 different products tested), gave permeation depthsvarying from 20 mm to 610 mm. The testing set-up can be seen in Figure 11.1.The best result was achieved by Rheobuild® 2000 PF, which of course is thereason why this has been selected as the standard admixture.

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The described test is one of the good examples that the tendency to focus onmaximum particle size or Blaine value to evaluate permeation properties ofdifferent cements, is the wrong focus. Fact is, with Rheocem® 650 and Rheobuild®

2000 PF the permeation depth is frequently almost the same as with Rheocem900.

Proper mixing can only be achieved in a colloidal mixer and the best result isproduced by:

• fill all the water into the mixer

• add all the cement while running the mixer and mix for 2 minutes

• add the Rheobuild® 2000PF and mix for another minute. Transfer to agitator

One practical example demonstrating the benefits of using Rheocem® microcement versus OPC is the Bekkestua tunnel in Oslo. The contractor VeidekkeAS partly used OPC only, partly a combination of OPC and Rheocem® andpartly the microcement alone. By keeping accurate records of the work progressand the achieved results over the 705 m tunnel length, a very interesting analysiscould be carried out by the site manager. Figure 11.2 gives the details of thisanalysis.

Figure 11.2 Time spent on injection with OPC and micro cement Rheocem.

As can be seen from the graph the time spent per kg injected OPC increasedtypically by a factor of 2 to 3 compared the use of micro cement. It also turnedout that the section of the tunnel with the highest recorded remaining leakageafter completion had been injected by OPC alone, thus demonstrating theefficiency of the micro cement system.

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11.2 Polyurethane grouts

Polyurethane (PU) grouts are quite useful in rock injection as a supplement tocement and other injection materials. Into this statement you should read thatPU is not really meant to be an injection material in its own right. This may be asurprise, but can be explained as follows below.

The viscosity is pretty high (as explained before), giving poor permeation incomparison to many other products.

It is a “dirty” material in the sense that PU sticks to anything it comes in contactwith and re-use of pipes, packers and valves becomes a hassle. However, welltrained and experienced staff will be able to handle PU without much difficulty.

It is unfavourable from a health viewpoint due to the isocyanate and risk ofallergy and respiratory problems. Again, using modern low risk products andprofessional staff with proper personal protection and applying good handlingprocedures, there is no high risk of problems.

PU needs special equipment, sometimes two-component pumps.

The material volume cost in place is high, depending on the actual foam factorin place.

The usefulness is primarily linked to the application of quick foaming productsthat can be used to block running water (typically when backflow into the tunnelis a problem), to locally fill larger openings and voids and sometimes to limitand control spread of the primary injection materials.

11.2.1 MEYCO MP 355 1K

The MEYCO MP 355 1K is such a quick foaming material and it has theadvantage of being one-component, so the pumping equipment is quite simpleto operate and has a reasonably low cost. The product is solvent free.

In most practical cases when used for running water cut-off it is beneficial tohave as short reaction time as possible. It is seldom a problem that the reactiontime gets too short, because the foaming goes on for a minute and more andduring this time a continued pumping will bring fresh material that createschannels in the foam. The targeted injection quantity will therefore not stopprematurely. The product comes in 25 kg cans with a 2.5 kg dosage of accelerator.This accelerator can be used partly or all of it, depending on the required reactiontime. The actual foaming reaction requires water and is triggered by first contactwith water. Be aware that also temperature of surroundings, water and producthas a strong influence on the reaction time. It is therefore normal to carry out

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site tests to determine the best dosage of accelerator. To give an idea aboutreaction times the following has been measured in the laboratory (with 10%accelerator and 10% water):

Initial temperature °C 5 10 15 20Start of reaction(seconds) 120 60 25 10End of reaction(seconds) 300 200 110 50Foam factor(free foaming) 25 25 25 30

Used under wet conditions (which is the rule) the application procedure is:

1. add the accelerator to the PU at the dosage established (2 to 10%) andmix it well.

2. inject with a suitable single component pump. Water in the ground willtrigger the foaming reaction.

It does happen that there is reason to inject under dry conditions (or in a situationwhere it is unsure if there is enough water in the ground). The procedure thenmust be modified by first pumping water into the rock or soil and then followingthis by the two steps above. This way you can make sure there is water totrigger the reaction.

When handling accelerated batches of the product, make sure that the workingplace is absolutely drip-free. Otherwise, one single drop of water into the mixedproduct or into the hopper of the pump will start the foaming reaction andequipment and hose may get clogged.

11.2.2 MEYCO MP 355 A3

This two-component product consist of the B component (isocyanate) which iscombined with the A component (polyol) to produce a foam end product. Thecomponents are delivered ready to use and the two-component pump must beset at 1:1 by volume of A and B (this is 1:1.2 by weight). The components areconveyed from the pump to the injection packer in separate hoses. Mixing takesplace through a static mixer and the mixed product goes through the packerinto the ground.

The chemical reaction of MP355 does not depend on contact with water, sinceall the necessary elements are in the A and B components. The A-componentmixed with B produce the following properties in the laboratory at 25 °C:

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Properties A3Density (g/cm3) 1.013±0.02Viscosity (mPas) 220 ±20Potlife mixed (s)Reaction time (s) 42-48Foam factor variable

In terms of ground water control and running water cut-off, the A3 is an alternativeto MP355 1K. However, the two-component product will normally be the firstchoice when using large volumes and against very much water. The A3 versioncan be made quicker by added accelerator, if necessary.

The MP355 A3 product comes in pails 30 kg (A) and 36 kg (B) or in drums of200 kg (A) or 240 kg (B). Containers and bulk is also available for larger quantities.

11.3 Acrylate resin grouts

11.3.1 MEYCO MP 301

MEYCO® MP 301 contains several acrylic esters and a methacrylamide derivativeas accelerator. In contrast to the acrylamide-based products, MEYCO® MP 301contains neither acrylamide nor formaldehyde. No acrylamide and noformaldehyde will be emitted during its application.

The primary substances of MEYCO® MP 301 are not harmful to human health:they are not acutely toxic, not neurotoxic, not carcinogenic, and show no negativeeffects on human reproduction. Most relevant are the irritating effects on skin,eyes, and mucous membranes. Repeated skin contact can cause allergicreactions. To minimise the risks of irritation and sensitisation, construction workersshould wear impermeable overalls, goggles, gloves, and rubber boots. All theserecommendations are printed on the containers and on the material safety datasheet.

All primary substances of MEYCO® MP 301 are biologically degradable.Regarding the ecotoxicity the acute toxicity toward fish and bacteria is low.Polymerised injection material of MEYCO® MP 301 has no ecologically relevanteffect.

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The product is a highly reactive hydrophilic resin that can be used for injectionin soil and rock. It is a two-component product, but the slower gel-times canallow the use of one-component pumps by mixing and injecting batches thatare pumped in shorter time than the chosen gel-time. The product is solventfree has no toxic components, can be used down to +3 °C and allow a choice ofgel-time as needed. Also the strength of the gel and subsequently the strengthof an injected soil can be adjusted by varying the concentration of the mixedproduct (by increasing the hardener concentration in component B and reducingthe volume of component B).

For ground stabilisation the MP301 is particularly well suited, since it gives astrong gel, but it is equally well suited for ground water control and mostly itrequires a two-component pump.

The product is prepared for use by adding a liquid accelerator to component A,while component B is prepared from potable water with up to 5% of the powderhardener. The two pre-made components are mostly combined at a 1:1 ratio(by volume). The mixed product will have the following general properties:

Property MP301 mixed Hardener comp. BForm liquid powderColour yellow whiteDensity 1.05pH 6-7Viscosity 1-2 mPas

When working with two-component systems the pump must be of stainlesssteel quality due to the aggressive component B. Containers used during injectionshould preferably be made of plastic.

11.4 Special product on silica basis

11.4.1 MEYCO MP 320 Colloidal Silica

MEYCO® MP 320 is a milky white nanometric colloidal silica suspension. Thewater dispersion contains discrete, non-aggregated spherical particles of 100%amorphous silicon dioxide in a 40% suspension, with 0,25 % concentration ofNa2O as a stabiliser. To give an idea about the particle size, remember thefrequently made statement that silica fume particles are like cigarette smokeand compare in Table 11.1 below. See also Figure 11.3 below.

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Table 11.1 . Comparison of particle size for silica products

Product Paticle size (�m) Specific surface(m2/g)

Colloidal silica (suspension) 0.016 80-900Silica fume 0.2 15-25Precipitated silica 5 10-15Fine crystalline silica 5 10-15Crystalline silica (mesh 200) 15 0.4

Figure 11.3 Relative size of colloidal silica nano-particle

The colloidal silica is a manufactured product and not a by-product from otherprocesses. This gives a very consistent product quality, reproducible performanceand the chemical structure makes the suspension fully stable with a shelf life ofminimum 6 months.

Figure 11.4 Gel time at 8 °C versus dosage of accelerator (component B)

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To use the colloidal silica suspension (component A) as an injection product wehave to add a component B, also termed accelerator. Depending on the dosageof the accelerator we can adjust the gel time between about 10 minutes andmore than 2 hours. The gel time will depend on temperature and must beestablished under site conditions. Figure 11.4 shows the relation betweenaccelerator dosage and gel time.

The product can be used between temperatures of +5°C and + 40°C and a onecomponent pump, like the cement grouting pump, will be suitable in most cases.The two components have to be pre-mixed in batches with the chosen volumeratio, before feeding the mix to the pump. Cleaning of the equipment is easilydone by water. None of the components contain toxic, aggressive or in any wayharmful substances.

MEYCO® MP 320 is available in standard sets containing component A in 210liter drums or 1000 liter containers, with accelerator (Component B) in 25 litercans or 210 liter drums.

The most important technical data are as follows (at 20 °C):

Property Component A Component B Mixed productColor Milky white TransparentViscosity mPas 9 1 5Density g/ml 1.3 1.07 1.25pH 9 - 10 7 9

As can be seen from the technical data, the product has a very low viscosityand it is well suited for all situations where penetration into fine cracks, jointsand pores is necessary.

The gelling behavior of MP320 is very favorable in the sense that the low viscosityis maintained until the preset gel time, when the viscosity increases rapidly. Thisis well demonstrated in the measurements presented in Figure 11.5.

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Figure 11.5 Viscosity development of MP320

The strength of the gel is similar to the traditional silica gel products, but MEYCOMP320 shows zero syneresis and no shrinkage. This creates very good watertightness and the ground strengthening effect is also noticeable in loose soils,running sand and in very broken rock. Like any other gel product, it will dry outand shrink if exposed for long time to atmospheric conditions at less than 100%humidity. This is not a problem under ground in soil and rock, when injected toseal off ground water. Compared to traditional silicate grouts, the chemicalstability is very much improved and the product can in many cases be used asa permanent grout. This must, however, be verified in each case due to variationin ground chemistry and the project requirements from site to site.

This product represents an entirely new opportunity in rock and soil injection,primarily because of the unique combination of positive properties:

• low materials cost for both components. Long shelf life

• no toxic, aggressive or hazardous substances in either component

• extremely simple handling, preparation, practical use and cleaning anddisposal

• easily adjustable gel time within a wide range (10 to 150 minutes)

• very low viscosity (5 mPas) until gelling, behaves like a true liquid in practicalterms

• zero syneresis gel with good chemical stability

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12. REFERENCES

[1.1] Davik, K, I., Andersson, H., “Urban road tunnels – a subsurface solutionto a surface problem,” Norwegian Tunnelling Society, Publication No. 12,Oslo 2002.

[1.2] Blindheim, O. T., Oevstedal, E., “Design principles and constructionmethods for water control in subsea road tunnels in rock,” NorwegianTunnelling Society, Publication No. 12, Oslo 2002.

[1.3] Houlsby, A. C., “Construction and design of cement grouting, a guide togrouting in rock foundations, John Wiley and Sons, New York, 1990.

[1.4] Fu, R., Sun, L. J., Wang, C. L., “Catastrophic water inflow in the newYung-Chuen Tunnel,” Proceedings of the AITES-ITA 2001 World TunnelCongress, Milan – Italy, 2001, Vol. III, pp 143-150.

[1.5] Stenstad, O., “Execution of injection works” (in Norwegian), Proceedingsof Post Graduate Training Course sponsored by the Norwegian CharteredEngineer Association and the Norwegian Rock mechanics Group,Fagernes, Norway, 1998.

[2.1] Karol, R. H., “Chemical Grouting,” Marcel Decker, Inc., New York, 1983.

[2.2] Norwegian Tunnelling Society, Handbook no. 1, “Injection in rock, practicalguidelines for injection strategy and methodology” (in Norwegian).

[2.3] Berge, K. O., “Water control – reasonable sharing of risk,” NorwegianTunnelling Society, Publication No. 12, Oslo 2002.

[3.1] Dahlø, T. S., Nilsen, B., “Sub-sea tunnelling – stability and rock cover” (inNorwegian with English Summary), Proceedings Norwegian TunnellingSociety yearly conference, Oslo 1991.

[3.2] Karlsrud, K., “Control of water leakage when tunnelling under urbanareas in the Oslo region,” Norwegian Tunnelling Society, Publication No.12, Oslo 2002.

[4.1] ISRM (1995): Final Report of the Commission on Rock Grouting.International Society for Rock Mechanics.

[4.2] De Paoli, B., Bosco, B., Granata, R., Bruce, D. A., “Fundamentalobservations on cement based grouts: Microfine cements and Cemillprocess,” International Conference Soil and Rock Improvement inUnderground Works, Milan, 1991.

[4.3] Mitchell, J.K., “Soil improvement – State of the Art Report”, ProceedingsX ICSMFE, Stockholm, vol. 4, pp 509-565, 1981.

[4.4] Lombardi, G., Deere, D., “Grouting design and control using the GINprinciple.” Water Power and Dam Construction, Volume 45, No 6.

[4.5] Keil et al, “Some new initiatives in cement grouts and grouting”, 42ndCanadian Geotechnical Conference, Winnipeg, 1989.

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[4.6] Melby, K., “Daily life of subsea rock tunnels – construction, operationand maintenance”, Proceedings of Workshop Strait Crossings – SubseaTunnels, Oslo, 1999.

[4.7] pers. comm. Operations Engineer Hans Ove Fostenes, Statoil, 1999.

[5.1] Lukajic, B., Smith, G. and Deans, J., “Use of asphalt in the treatment ofdam foundation leakageStewartwill Dam”, Seminar on issues in damgrouting, ASCE Spring Convention, Denver, Colorado, April 1985.

[5.2] pers.comm. Paddy Cochrane, FEC Inc., Mascot, TN 37806, USA

[6.1] Skjeggedal, T., “The use of tunnel boring machines (TBM)”, NorwegianTunnelling Society, Publication No. 2, Oslo 1983.

[6.2] pers.comm. Timothy Avery, Master Builders Inc.

[6.3] Schunnesson, H., “Probing ahead of the face with percussive drilling”,Tunnels & Tunnelling, January 1996, pp 22-23.

[8.1] Mueller, R., “Contemporary grouting equipment”, CUC courseWaterproofing of Tunnels, Switzerland, 2000.

[10.1] Karlsrud, K., “Leakage requirements in connection with the new roadtunnel “Fjellinjen” through Oslo”, Proceedings Norwegian TunnellingSociety yearly conference, Oslo 1987.

[10.2] Holter, K. G., Johansen, E. D., Hegrenaes, A., “Tunnelling through asandzone: Ground treatment experiences from the Bjoroy subsea roadtunnel”, Proceedings of North American Tunnelling ’96, vol. 1, pp 249-256, Washington DC, 1996.

[10.3] Stille, H., “Swedish research regarding grouting of rock – 30 years”,Proceedings of the Rock mechanics day 1977, Swedish RockEngineering Research Foundation, Stockholm, 1977.

[10.4] Erikson, A, Palmqvist, K., “Experiences from the grouting of the Lundbytunnel”, Proceedings of the Rock Mechanics day 1977, Swedish RockEngineering Research Foundation, Stockholm, 1977.

[10.5] Haessler, L., Forhaug, M., Experience of grouting works at the Arlandatrain project”, Proceedings of the Rock Mechanics day 1977, SwedishRock Engineering Research Foundation, Stockholm, 1977.

[10.6] Sundin, N. O., Karlsson, B., “The Snake – a TBM driven tunnel inStockholm, prognosis and evaluation of excavation”, Swedish RockEngineering Research Foundation, Report 451:1/92, Stockholm, 1989.

[10.7] Hahn, T. et al, “Tunnel boring in the city of Stockholm, the Saltsjoe tunnel,summary of project”, Swedish Rock Engineering Research Foundation,Report 220:5/89, Stockholm, 1992.

[10.8] Kveldsvik, V., Karlsrud, K., “Support methods and ground water control”,Norwegian Tunnelling Society, Publication No. 10, pp69-77, Oslo 1995.

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Pre-Excavation Groutingin Rock Tunneling

Americas

Master Builders, Inc.Shotcrete &Underground Systems23700 Chagrin Blvd.Cleveland, OH 44122Tel: 216-839-7500Fax: 216-839-8827

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Europe

MBT InternationalUnderground Construction GroupDivision of MBT Switzerland S.A.

Vulkanstrasse 1108048 Zurich, SwitzerlandTel: 41-1-438-2210Fax: 41-1-438-2246

Meyco EquipmentDivision of MBT Switzerland S.A.

Hegmattenstrasse 248404 Winterthur, SwitzerlandTel: 41-52-244-0700Fax: 41-52-244-0707

Bettor MBT, S.A.Duero, 23Poligono Industrial Las Acacias28840 Mejorada del Campo (Madrid)Tel: 34-91-668-0900Fax: 34-91-668-1732

www.ugc.mbt.com/

Knut F. GarsholM.Sc. Engineering Geology

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