Education Under Ground Mining E Book 04

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First edition 2008www.atlascopco.com

Raiseboringin Mining and Construction


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Atlas Copco Rock Drills AB

www.atlascopco.com

Turning heads and pulling the string

A tough environment demands tough machines.

Machines built for tight places able to squeeze out

the most productivity in the least amount of time.

Machines that are versatile, reliable, cost-efficient and

with the highest rate of penetration and safety on the market.

No other company has the experience, the innovation and

the commitment to the industry like Atlas Copco.

Whatever the rock, wherever you are. Weve got the

raiseborer to fit your application. Count on Atlas Copco,

(We wont string you along)

Committed to your superior productivity.


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RAISEBORING 1

Foreword

2 Foreword by Marcus Eklind, Product Line Manager,Raiseboring, Atlas Copco Rock Drills AB

Talking technically

3 Rock drillability

7 History of raiseboring

10 The raiseboring concept

13 The raiseboring machine

20 Computer based training for raiseboring

22 Horizontal and low angle boring

25 Development of boxhole boring

29 Down reaming

33 Modern boxhole boring with BorPak

36 Selection of raiseborer drive system

38 Computers improve rock excavation productivity

40 Site preparation

47 Operating the raiseborer

51 Bailing considerations

56 Cutter and reamer design

64 Raiseboring drillstring components

Case studies

67 Boxhole boring at El Teniente

73 Raiseboring for production at McArthur River78 Replacing Norways Tyin hydropower plant

Product specifications

82 Robbins raiseboring machines

91 Pilot bits from Atlas Copco Secoroc

96 Drill string components

99 Power packs

101 Drill pipe handling equipment

102 Transporters

103 Tools

104 Raiseborer system upgrade kits108 Conversion table

Contents

Produced byAtlas Copco Rock Drills AB, SE-701 91 rebro, Sweden, tel +46 19 670 70 00, fax 019-670 73 93.Publisher:Marcus Eklind, [email protected] Production Manager:Elisabeth Nilsson, [email protected]:Mike Smith, [email protected] Senior Adviser:Hans Fernberg, [email protected]

Contributors:Bjrn Samuelsson, Jan Forsberg, Johnny Lyly, Mikael Bergman, Rikard Erlandsson, Roberto Lopez, Sverker Hartwigall [email protected], Steve Brooke, [email protected]

Digital copies of all Atlas Copco reference edit ions can be ordered from the publisher, address above, or online atwww.atlascopco.com/rock.Reproduction of individual articles only by agreement with the publisher.

Edited byMike Smith, tunnelbuilder ltd, United Kingdom. Designed and typeset byahrt, rebro, Sweden. Printed byWelins Tryckeri AB, rebro, Sweden.

Legal notice

Copyright 2008, Atlas Copco Rock Drills AB, rebro, Sweden. All product names in this publication are trademarks of Atlas Copco.Any unauthorized use or copying of the contents or any part thereof is prohibited. This applies in particular to trademarks, model denominations,part numbers and drawings. Information in this publication is provided as is. Atlas Copco Rock Drills AB disclaims any representation or warrantiesof any kind including without limitation warranties of merchantability or fitness for a particular purpose, non-infringement or content. In no eventwill Atlas Copco Rock Drills AB be liable to any party or any damages for any use of this publication. The contents, including illustrations and photos,in this publication may describe or show equipment with optional extras . It may also contain references to products or services that are not availablein your country. This publica tion, as well as specifications and equipment , is subject to change without notice. Consul t your Atlas Copco Customer

Center for specific information.

Front cover: Robbins 34RH C at the Kvarntorp test mine in Sweden


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2 RAISEBORING

ForewordAgeneration ago, excavating raises was hard and dangerousmanual work, carried out by only the most experienced miners.Mines needed ore passes and ventilation raises, and there

was only one way to excavate them, using drill/blast. WhenJames Robbins built the prototype Robbins 41R raise drill in1962, it was the beginning of a new era. Boring of raises wasfar more attractive than traditional methods. It was faster,cleaner, and, above all, took the operators out of the raisesand placed them in accessible, well ventilated, and safepositions.

From the Robbins 41R to the current model 191RH, theRobbins raise drill has come a long way. Both in the capa-bilities of the machine, and in the technology behind it. Ourraise drills are now capable of boring holes 1,000 m-long,and up to 6 m-diameter. As a result, raiseboring is now thepreferred, and most cost-effective, means of excavatingopenings in underground projects.

Increased automation is a continuous trend in the businessof raise drilling. The reasons for this are simple, and can be

summarized as: reduced labour; faster and smoother operation;quicker response to blocky ground; and data logging anddiagnostics. New control systems ensure that the operator

can select the optimal running parameters to get the mostout of the raise drill, both in performance and economy.Functions such as automatic shutdown and anti-jammingmake it possible to carry on drilling between shift changes,without worrying about spin backs or losing the drill string.

As the hydraulic drives have developed and become moreefficient, the improved control accuracy has made them thefirst choice for most customers. Hydraulic drives offer goodreaming characteristics and are very soft on the drill string.Combined with the new reliable control system, this is prov-ing to be the way forward in most operating environments.

This book is designed as a reference for all raise drillers,describing the methodology in detail, and giving an insightinto the current equipment offering from Atlas Copco. Wehope you find it useful, and we are available to discuss thefiner points with you at any time.

Marcus Eklind

Product Line Manager, Raiseboring

Atlas Copco Rock Drills AB

[email protected]


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RAISEBORING 3

Rock properties

Data on unconfined compressive strength

(UCS) is the most commonly available

rock property. However, it is difficult to

use UCS to predict d rilling perfor-mance without additional information.

The average UCS for selected forma-tions is shown in Table 1 (next page).

One simple method to determine theapproximate hardness of a formation isthe Moh scale, if UCS information isunavailable. The Moh scale is used toclassify the relative hardness between

different minerals. Diamond is at the topof the hardness scale, rating a 10, andtalc is at the opposite end, rating a 1.In general, the minerals at the high endof the scale are harder than those on thelow end of the scale. Scratch testing can

be used to estimate the hardness: a fin-

gernail can scratch up to about 2 Mohs,a copper coin up to about 3 Mohs, and

glass up to 6 Mohs. However, care mustbe taken to ensure that the scratch isnot a powder residue left from the itembeing used to scratch. Some commonminerals and rocks are shown with their

corresponding Moh Hardness number

in table 2 (next page).Other factors that influence drilla-

bility are:Abrasiveness abrasiveness of a for-

mation is usually indicated by its silica

content. Abrasive formations accelerate

cutting structure wear, causing slowerdrilling rates as the carbide becomesblunter, and sometimes cone shell ero-sion, which can ultimately lead to lostinserts.

Jointing and bedding formationswith joints or layers are easier to drillthan massive unfractured formations,

since the anomalies provide free faceswhich make failure easier.

Schistocity schists have layers ofmica interbedded with harder, morebrittle rock. These mica layers absorbthe energy of the drilling process, with

the rock acting as a plastic, rather thana brittle material.

Rock failure

The primary failure mode employed bythe rotary drilling method is the tensile

failure of the rock under a compressiveload to form rock chips. In weaker,more ductile formations this primarymethod of failure may be replaced oraugmented by the gouging and scrapingaction of the cutter. Studies have shown

that the action of the cutting element isprogressive, as shown in Figure 1.

As force is applied to the cutting

element, the cutter deforms the rock.As the force increases, a pressure bulb

Rock drillability

Fracturing rockDrillability is the ability to frac-ture or drill rock using mechanicalmeans, and is governed by a num-ber of factors. Some of these arerelated to the rock formation, andothers to the forces applied, andthe geometry of the drilling equip-ment. Rock properties, rock fail-ure mechanisms, and drilling para-meters all relate to drillability, andare helpful in evaluating drillingefficiency, trouble shooting pro-blems, and estimating cutter per-formance.

General rock boring principlesand their practical application arethe basis of modern raiseboring.Two basic principles are used to-gether in full face boring - theseare cratering and kerf breaking.The objective when boring is tocrush the rock until tensile crack-ing occurs, causing chips to breakaway. The art is in the design ofthe cutters and the pressure withwhich they are kept in contactwith the rock. This is where ex-perience counts, and nobody hasmore knowledge about raise bor-

ing than Atlas Copco Robbins.

Figure 1: Cratering is the first stage of kerf breaking.

Zone of triaxial

crushing Radialcracks


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TALKING TECHNICALLY

4 RAISEBORING

of finely crushed rock forms under thecutter. The pressure bulb transmits pres-

sure to the surrounding rock, causingtensile fractures. As these propagate to

the rock surface, chips form, releasingthe pressure of the pressure bulb.

Rock breakage also relies upon the

interaction of several cutting structureelements and their contact points onthe rock. The placement of the cuttingstructure elements is a critical part ofthe cutter design.

Cutting structures

Atlas Copco uses three types of cuttingstructure geometry for raiseboring appli-

cations: kerfed carbide insert cutters;

rowed cutters; and randomly-placed car-bide insert cutters.

Kerf, or disc cutters use an extension

of the rock failure mechanism described

above. When properly-spaced discs arecombined with sufficient cutter force,

very efficient drilling results, since the

disc maintains continuous contact with

the formation.

Interaction between adjacent discpaths produces shear failure of the rockbetween these paths. Figure 2 demon-

strates the pattern of a kerf type cutteron the rock face.

Kerf cutters tend to spall out 10 -20 cm(4 to 8 in) long banana shaped chips andsmaller, almost circular chips depen-

ding on the formation and the loading.Compared to randomly placed carbideinsert cutters, kerf cutters tend to require

higher thrust and torque to spall outchips, but are more efficient if sufficient

load and torque are available. The kerfcutter concept is shown in Figure 4.

Carbide rowed cutters perform some-

where between the kerf-type cutter andthe random insert-type cutter. The rowed

cutter design has multiple rows of in-serts, but no steel kerfs in which theinserts are located. The lack of kerfsallows more room for cuttings removal,less opportunity for abrasive formations

to wear away the cutter shell, and greater

penetration of the inserts into the for-mation with less power consumption.The staggered insert location and mul-tiple rows tend to decrease the torquerequirements, somewhat similar to therandom cutting structure, and the rows

of inserts allow for rock kerfs to spallout of the formation, although generallysmaller than a pure kerf cutter design.

The patented design of random in-sert cutters employs a random patternof inserts on the cutter shell to provide

Formation UCS (Psi) Mpa Formation UCS (Psi) Mpa

Berea Sandstone 2,500 17 Limestone 20,000 138

Austin Chalk 3,000 21 Marble 20,000 138

Sandstone 9,000 62 Dolomite 24,000 165

Quartzitic Sandstone 9,000 62 Porphyry 40,000 276

Shale 15,000 104 Pink Quartzite 68,000 469

Table 2: Moh hardness numbers for selected common minerals and rock.

Mineral or Rock Moh Hardness Mineral or Rock Moh Hardness

Amphibolite 6.2 Gypsum 1.5

Andalucite 7.5 Limestone 3.3

Andesite 7.2 Magnesite 3.5

Basalt 7.0 Magnetite 4.2

Bituminous Coal 2.5 Marble 3.0

Chert 6.5 Potash 2.2Cryolite 2.5 Pyrite 6.2

Diabase 7.8 Quartz 7.0

Diamond 10.0 Quartzite 7.0

Dolomite 3.7 Ryolite 7.2

Emery 8.3 Salt 2.5

Feldspar 6.2 Sandstone 3.8

Gabbro 5.4 Slate 3.1

Gneiss 5.2 Soapstone 1.0

Granite 4.2 Sulphur 2.0

Graphite 1.0 Zircon 7.5

Table 1: Average UCS for selected formations.

Figure 2: Kerfs on the rock face.

Figure 3: Random pattern on rock face.


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Life = Function (force to the powerof 3.33). In the previous example, ifthe 40,000 lb cutter load results in a1,000 hr bearing life, then the 50,000lb force would result in 1,000 hours x(40,000/50,000) 3.33 = 475.7 hr.

The actual load applied to each cuttermust be used for this application, andthe load must be broken down into axialand radial load in the bearing, for a clo-ser estimate.

The reduced life is even more pro-

nounced when the cutters are consid-ered as a system. For example, the abovecalculation may be accurate when onecutter is considered, but what if thereare 10 cutters in the system? If the oddsare that there will be one failure in 100,or 1%, in that period of time, the chancesof failure increase as the number of cut-

ters increases.In addition, too little force may also

be detrimental to the life of the cuttingstructure on the cutter. If the appliedload is insufficient to fracture the for-

mation (minimum of 80% of the UCSassuming a 1 square inch contact area

per cutter), the inserts will wear rapidly.

This failure is enhanced in abrasiveformations.

Rotary speed and torque

Rotary speed generally affects drilling ra-

tes linearly. For example, a 10% increasein rotary speed should produce a 10%increase in drilling rate. The traditional

approach to rotary speed recommen-dations has been to limit the peripheral

speed of the head to under 350 ft/min.These limitations have been set due toconcerns over gauge wear on the head,drill string wear, and drill string failure,

all of which have occurred at high peri-pheral speeds. Higher rotational speedsare incorporated into smaller raiseboring

machines, but caution must be exercisedwhen using high rotational speeds onlarge diameters.

The relationship between rotary speed

and bearing life is also linear, but is

negative, leading to a 10% decrease inbearing life as a consequence of a 10%increase in rotational speed.

Increases in penetration rate due toincreases in rotational speed are not as

dramatic as penetration rate increases

due to increased cutter load, but shouldnot be discounted. Often, the increased

speed is within the capability of thedrilling machine, with the consequencebeing increased power consumption.

Insofar as drilling torque is con-cerned, capacities of equipment oftendictate the load that can be applied to thecutters. Several factors influence torque

requirements, such as load per cutter,reamed diameter, formation, and angle

of the raise. Additionally, the torque re-quirements tend to fluctuate radically,with peak torque more important thanaverage torque.

All things being equal, the torque re-

quired increases as the load per cutterincreases, as the diameter of the raise

increases, and as the angle of the raiseincreases away from vertical.

Formation can be more difficult toclassify in regards to torque require-ments. However, in general, the softerthe formation, the deeper the insert pe-

netrates, and the higher the torque re-quirement. This relationship can bealtered considerably if the rock failsreadily through shear, as in some verti-

cally jointed formations. Broken andblocky formations can also produce

large spikes in the required torque asthe formation tries to unravel.

Steve Brooke

Penetration Rate Vs. UCS

0 1 2 3 4

0 10000 20000 30000 40000 50000 60000 UCS

Penetration

Rate

n = 1.4

n = 1.6

n = 1.2

n = 1.8

Figure 5: Random pattern on rock face.

CrateringCratering is the term used to describethe crushing action in the rock di-rectly beneath the contact area of thecutter edge, which is usually a chiselshaped tungsten carbide insert. As in-creased loading is reacted into the rock

by the cutter, it is crushed to a f inepowder and compressed. The induced

stresses initiate radial tensile cracksin the rock mass, which break backto the free surface. As penetration ofthe cutter edge into the rock continues,the cracks expand, and chips splitaway. This allows the crushed fines to

escape and new tensile cracks to form.In this way, continuous production ispossible by simply keeping the rotating

bit pressed against the face.

Kerf breakingKerf breaking occurs when radiatingcracks beneath the cutter edge reachan adjacent kerf and form a chip be-tween the two cutter kerfs. Kerf brea-king is applied to the entire rock face

by a reamer dressed with either singlerow disc cutters or multi-row buttoncutters. These are mounted on the rea-

mer at spaced intervals outward from

its centre. As it rotates and is thrustforward into the rock face, the cuttersroll against the surface of the rock andcrush kerfs in concentric paths. Once

the critical depth of penetration to spa-cing ratio is reached for the particularrock type being bored, chipping occurs

between the kerfs, and the rock face

can be systematically excavated.


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RAISEBORING 7

Market share

The history of raiseboring is reallythe history of Robbins raise drills. Asthe industry pioneer, the company hasmanufactured 350 raise drills of theapproximate 600 that have been pro-duced in total to date, giving it a +60%

market share. In all, some 35 models have beenintroduced, with reaming diameters of0.6 m to 6.0 m.

Of the models produced, the 73RMis the most sold, with a reaming diameter

of 1.8 m-3.1 m.Nearly all of these Robbins raise

drills are st ill available for work. So,despite always requiring high capitalinvestment, raise drills have given anexceptional return to their owners whileretaining solid residual value. This sumsup the raiseboring story.

Apart from mechanizing the singu-larly most dangerous job in mining,

these machines have proved to be awise investment all round.

Built for life

When James Robbins built the first raise

borer in 1962, lit tle would he havethought that it would still be working45 years later. However, the fact is that

the very same 4 ft-diameter machine,

the original Robbins 41R as shown inFigure 1 with pinned drill tubes andsteel cutters, was recently reported asworking in Morocco.

By 1966, rapid development on thepart of Robbins had established industry

standards for tungsten carbide cutters,and a f loat box to reduce stresses inthe main bearing and drill string of the

raiseboring machine. Connectors usingAPI-standard 7-inch tapered threadswere introduced to connect the drilltubes on the second machine built byRobbins and was in use in various sizes

unti l the DI-22 thread was invented in1969. This proved to be a well func-tioning and reliable connection.

In 1967, Robbins upped its gamewith the introduction of the Robbins

History of raiseboring

Forty five years onIt is now 45 years since Atlas Cop-co Robbins built the worlds firstsuccessful raiseboring machine,and launched a worldwide revo-lution in underground mining andconstruction that is still gainingmomentum. New products, concepts andtechniques, such as automation,computerization and horizontalreaming are creating exciting newopportunities for the user under-ground. The latest innovation is the ap-

plication of Atlas Copcos CAN-buscontrol technology to raiseborers,using components that are com-mon to other new generation pro-ducts such as Rocket Boomer andSimba drill rigs that may alreadybe at work on the mine. In this way, mechanization forone-man operation is facilitatedwithout having large inventoriesof spares, and with very short lear-ning curves for all concerned.

Figure 1: The Robbins 41R, first of a long line of raise drills.


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61R, capable of reaming a 6 ft-diameter

hole. This became the most-sold ma-chine in the world, reaching volumesof 50-60/year in the early-1970s. The61R became the 63R, as shown in Figure2, and is now the 73RM and the currentmarket leader with the biggest volume

sales to date.

From 1971-73, larger machines suchas the Robbins 83R were developed tosatisfy a demand for bigger diameterboreholes. All machines built before1973 were equipped with two-speed AC

motors, but from then onwards, DCdrive and hydraulic drive became thenatural choice.

The first boxhole borer appeared in1974, giving miners the option of exca-vating raises where there is limited orno access to the upper level. The raise-

borer is set up at the haulage level anda full-diameter raise is bored upward,

with the cuttings gravitating down thehole for removal. Within ten years, theRobbins BorPak was launched, facili-tating boxhole boring without a drillstring, making the operation vastly more

efficient and easy to set up.

Improved methodology

Since Robbins introduced to the mi-ning industry the first machine builtexclusively for raiseboring, the advan-tages over older methods have becomeincreasingly evident.

Foremost among these is safety, asworkers are not required to be in theraise during the excavation process. The

inherent dangers of rock falls, fumes,and the handling of explosives areeliminated.

The second advantage is speed ofoperation. Even early on, Robbins raise

boring machines achieved milestonesby reaming 150 ft (46 m) raises in softgranite at two-week intervals. These had

previously taken several months usingthe older methods.

Before long, bored raises exceeding1,000 ft (305 m) became common. Raisediameters of over 20 ft (6 m) have nowbeen bored in medium to soft rock.

Single passes in hard rock are ap-proaching 3,280 ft (1,000 m) in length.Raiseboring machines have proved su-perior and more economical when com-pared to the drill and blast methods ofraise excavation. They have also opened

new opportunities for mine planning,offering more opportunities for lessdevelopment investment and earlierproduction.

Another advantage is that, becausethere is no blasting, the rock is not shat-tered. The result is a smooth interiorraise surface, which allows for moreefficient movement of ore and air, andprovides maximum wall stability.

Finally, mechanization with raise bo-ring machines requires less manpoweroverall. Skilled conventional miners,always in short supply, are not neededto operate a raiseboring machine. Lesstotal manpower, less rock to handle,

less construction time, and increasedsafety all add up to earlier profits.

Figure 2: Robbins 63RM was predecessor to the worlds most sold raise drill, the Robbins 73RM .

Figure 3: Atlas Copco Jarva raiseborer.


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Acquisitions

In the late 1970s, Robbins boughtIngersoll Rands raiseborer division,with its well-regarded tungsten insertcutters, which to this day are acknow-

ledged as the best available. Robbinsimmediately switched from Reed cut-ting tools to those of its own manufac-ture, and has since supplied them withevery raiseborer produced. IngersollRand had itself built some 30 raise bo-ring machines prior to the takeover byRobbins. Another acquisition by Robbins

was that of Drillco Texas when it wasunder Chapter 11 administration.

In 1980, Atlas Copco bought theJarva Company, based in Solon, Ohio.

Four very advanced raiseboring ma-chines were built in 1982-1983 as shown

in Figure 3, with variable speed drives

and computer control as shown in Fi-gure 4. These machines are today ope-

rated by Dynatec in North America.

Future trends

The current trend is towards compute-rization of the raiseboring operationusing Atlas Copcos patented Rig Con-

trol System (RCS). This is CAN-busba se d, with a si ng le power cableservicing all of the electric units, andanalog or digital switches controllingthe use of the electrical power. Thedigital signal is superimposed on thepowerline, and a computer listens tothis, and sends out instructions in the

same manner. Two tiny wires have beenadded to cope with the signalling, and

sometimes two powerlines are required.

The CAN-bus system is very reliable,flexible and easily expandable. Newunits can be added anywhere on themachine, without adding another cable.It has become very popular in the forest

and textile machine industries, and mostcars, trucks and construction vehiclesare, or will be, equipped with this system

in the future.RCS gives the operator greater con-

trol over the machine, with some of themore mundane aspects of the boringprocess computerized, leaving him free

to concentrate on the more complexaspects. The result is that a single ope-rator can now control all functions on a

raiseborer, including rod changing.

Marcus Eklind

Figure 4: The control console of the Atlas Copco Jarva raiseborer.


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Raiseboring process

In raiseboring, the machine is set up atthe surface or upper level of the twolevels to be connected as shown in Fi-gure 1. A small pilot hole is then dril-led down to the lower level using a drillbit attached to a series of cylindricaldrill pipe pieces, which form the drillstring. Upon completion of the pilot hole,a reamer with a diameter larger thanthe pilot hole is attached to the drill

string at the lower level. Using the rea-

mer, the small pilot hole is reamed back

to the machine on the upper level. Thecuttings excavated by the reamer fallto the lower level and are removed by

any convenient method.

Applications

Raiseboring machines have been usedin both mining and civil projects forholes in the range 0.6-6.0 m-diameterand up to 1,000 m-long. Some specificapplications of bored raises are:

Mining: materials transport; ventilation;

manriding; mineral production.

Civil:hydro penstocks and surge cham-

bers; redirection and retrieval of hydro

water; petroleum, pressurized gas, and

nuclear waste storage; road and rail tun-nel ventilation; stormwater storage and

drainage; access for pipes, hoses, andcables; water inlets and outlets for fishfarms.

Horizontal and low angleraiseboring

Standard raiseboring machines are ca-pable of boring raises at angles f romvertical to 45 degrees from horizontal.Raises from 45 degrees to horizontal

The raiseboring concept

ParticularterminologyThe raiseboring concept involvesterminology that is a little diffe-rent from normal mining language.Raiseboring, also called raise dril-ling, is the process of mechanicallyboring, drilling, or reaming a ver-tical or inclined shaft or raise be-tween two or more levels. All le-vels may be underground, or onelevel may be at the surface. During the early developmentof mechanical raise excavation,

different approaches were pursuedand, in several cases, systemswere developed. The most suc-cessful method became known asraiseboring. Today, raiseboring is acceptedas the world standard for mecha-nical raise excavation, and thename of Atlas Copco Robbins issynonymous with the technique.

Figure 1: Raiseboring process.

Figure 2: Low angle raiseboring.


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RAISEBORING 11

have been completed with the additionof only a few accessories and minoradjustment of the standard machine asshown in Figure 2.

Other methods of vertical

boringOther methods of mechanical raise andshaft excavation have been developed in

addition to raiseboring. These methodsare described in the sections below andare as follows: boxhole boring; blindshaft boring; down reaming; pilot down

- ream down; hole opening; BorPak.

Boxhole boring

Boxhole boring is used to excavate rai-

ses where there is limited or no accessto the upper level. Here, the machineis set up at the lower level and a fulldiameter raise is bored upward.

While boring upward, stabilizers areperiodically added to the drill string toreduce oscillation and bending stresses.

The cuttings are carried by gravity down

the hole, and are deflected from themachine and removed at the lower level.Boxhole boring can be completed withor without a pre-dr illed pilot hole, asshown in Figure 3.

Blind shaft boring

Blind shaft boring is used where thereis access to the upper level of the pro-posed raise, but limited or no access to

the lower level. With this method, theraise is excavated from the upper leveldownward using a down reaming sy-stem connected by a drill string to themachine above. Weights are added to the

reamer mandrel as shown in Figure 4.

Stabilizers are located above andbelow the weight stack to ensure verti-

cal boring. A reverse circulation sy-stem, or a vacuum system, is typicallyused to remove the cuttings out of theshaft.

Down reaming

Down reaming begins by drilling aconventional pilot hole, and then en-larging it to the final raise diameter by

reaming from the upper level to the lo-wer level as shown in Figure 5. Larger

Figure 3:

Boxhole boring.


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TALKING TECHNICALLY

12 RAISEBORING

diameters can be achieved by conven-tionally reaming a pilot raise, and then

enlarging it by down reaming.During reaming, the cuttings gravi-

tate down the pilot hole, or reamed hole,and are removed at the lower level. Toensure sufficient down reaming thrust

and torque, the down reamer is fittedwith a non-rotating gripper and thrustsystem, and a torque-multiplying gear-

box driven by the drill string. Upper and

lower stabilizers ensure proper kerf cut-

ting, and reduce drill string oscilla-tions.

Pilot down, ream down

This method, also known as hole open-ing, is used to enlarge an existing pilot

hole with a small-diameter reamer. Theoperation is similar to pilot hole drill-ing, the only difference being that a small

reamer is used instead of a pilot bit.The small reamer is designed to use theexisting pilot hole to guide the drilling.Stabilizers are used in the drill stringbehind the reamer to prevent it frombending. Pilot down, ream down holeopening is only used when a standardreaming system is either impracticalor impossible, as shown in Figure 6.

BorPak

The BorPak system is used for blind holeboring. It comprises a guided boringmachine, a power unit, a launch tube/transporter assembly, a conveyor, and an

operator's console. The BorPak operates

like a microtunnelling machine, climb-

ing up the raise as it bores. Cuttings pass

through the centre of the machine, fal-ling down the raise and launch tubeonto a conveyor. This revolutionary ma-

chine has the potential to bore from 3.9to 6.6 ft (1.2 - 2.0 m) diameter holesat angles as low as 30 degrees. Like araiseboring machine, the BorPak offershigh speed drilling, but eliminates theneed for a drill string. It also pro-vides the steering flexibility of a raiseclimber. BorPak is especially attractive

when f lexibility and mobility are ata premium, or when the job requiresdrilling a series of short raises.

Roberto Lopez

Figure 4: Blind shaft boring.

Figure 5: Down reaming.

Figure 6: Pilot down, ream down.


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Derrick assembly

The derrick assembly supplies the ro-tational and thrust forces necessary toturn the pilot bit and reamer as well asto raise and lower the drill string. Thisassembly consists of several major com-

ponents. These are: base plates; main-frame; columns; headframe; hydrauliccylinders; and drive train assembly.

Base plates

The base plates, left-hand and right-hand, provide the structure for suppor-ting the weight of the derrick assemblyas well as for positively transferring theforces required for raiseboring into thederrick mounting system.

The base plates are normally set ona level concrete foundation pad and an-chored by rock bolts passing throughthe pad into the rock formation below.

In some instances, the base plates aremounted to a steel beam system, whichin turn is secured to concrete founda-tion pads and the rock formation.

Mainframe

The mainframe is the major load bear-ing structure of the derrick assembly.It is mounted and secured on the baseplates with removable turnbuckles andexpansion pins. Each turnbuckle con-

sists of two threaded eyes screwed intoa turnbuckle body. The turnbuckles

establish and maintain the requiredboring dip angle. After the boring angle

is confirmed, the expansion pins are

tightened to provide linkage between themainframe and turnbuckles, and the base

plates and turnbuckles, for the positive

transfer of boring forces.Removable pivot brackets mounted

at the rear of the mainframe allow thehydraulic cylinders of the transportersystem to be attached to the mainframefor derrick erection and takedown.

These brackets also serve as rests for

the derrick assembly when loaded onthe transporter. The mainframe is equip-

ped with a worktable. This is designedwith a hollow centre to allow passage

of drill string components from the drive

train assembly into the pilot hole. Theplane of the worktable top surface re-

mains perpendicular to the axis of thedrill string at all dip angles.

All worktables are equipped with, orare used in conjunction with, a work-table wrenching system. This reacts themachine torque into the mainframe for

threaded connection makeup and break-out. The wrenching system is also usedto hold the drill string and the cuttingcomponents securely in the hole whenadding or removing parts.

The worktable also provides moun-

ting for various accessories necessaryfor raiseboring machine setup and

The raiseboring machine

Thrust and rotationThe raiseboring machine (RBM)provides the thrust and rotationalforces necessary for raiseboringas well as the equipment and in-struments used to control and mo-nitor the raiseboring process. The RBM is composed of fivemajor assemblies described in thesections below. These are: derrick;hydraulic system; lubrication sy-stem; electrical system; and con-trol console supplied with eachmachine.

Figure 1: Derrick assembly layout .


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TALKING TECHNICALLY

14 RAISEBORING

operation, such as the pilot hole starterbushing, the outlet housing of the blo-oie system, the drivehead installationand removal tools, and the ram assem-bly, if fitted.

Columns

Chrome plated cylindrical columns pro-vide torque transfer from the drive train

assembly into the mainframe. These co-

lumns are connected at their bottom to

the mainframe, and at their top to theheadframe. They pass through machined

bushings in the crosshead, and guidethe crosshead as it travels up and down.

Headframe

The headframe is mounted atop the

derrick assembly columns, linking themtogether. This dampens column vibration,

and shares the boring torque betweencolumns. The headframe is most com-monly secured to the columns by use of

a bolted crown gear coupling system.

Hydraulic cylinders

The hydraulic cylinders supply the thrust

required for raising and lowering thedrill string in relation to the raise bo-ring machine. These same cylinders also

supply the thrust necessary for bothpilot hole dril ling and raise reaming.Extra thrust capacity is often providedin the design of these cylinders to dealwith special circumstances.

Drive train assembly

The drive train assembly supplies to the

drill string and cutting componentsthe rotational power necessary for raise

boring. General descriptions of the three

major components making up the drivetrain assembly are given below. Theseare: crosshead; main drive motor; andgearbox.

Crosshead

The crosshead is a moving platform towhich the main drive motor system andgearbox are mounted.

Driven by the hydraulic cylinders and

guided by the columns, the crossheadraises and lowers the drill string andtransfers torsional forces into the raise-

borer columns.Most Atlas Copco Robbins raise bo-

ring systems utilize the crosshead as areservoir for the gearbox lubrication oil.Other lubrication system components,

such as the lubrication motor and pump,can also be housed in the crosshead.

Figure 2: Exploded view of derrick assembly.

Main Drive

DC Hydraulic AC

Headframe

Mainframe

Hydrauliccylinder

Machineworktable

Turnbuckles

Turnbuckles

Expansion pins

Expansion pins

Gearbox

Columns

Hydraulic cylinders

Drivehead

Crosshead

Baseplates


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TALKING TECHNICALLY

RAISEBORING 15

Main drive motor system

The main drive motor system of thederrick assembly supplies the rotationalpower necessary for raiseboring. Fourtypes of main drive motor systems canbe used with Atlas Copco raiseboringmachines. These systems are: AC, DC,hydraulic and VF.

The AC system has the simplest de-sign, lowest cost, and highest reliabilityof all raise drill drive motor systems.It features fixed speed and fixed tor-que, and is best suited to competentground, where minimum motor stallingwill be encountered.

DC drive is variable speed and va-riable torque, and is best suited for lar-ger raise diameters in mixed ground

conditions.Hydraulic drive, employing variable

speed and good torque limiting control,is suited for use in all ground condi-tions and has high reliability.

The VF drive system, developed in-house by Atlas Copco, combines thesimplicity of the AC drive motor sy-stem with exact motor speed, torque,and positioning control.

The VF system circuitry controls the

speed, torque, and position of its AC

motor by first converting the incoming

AC mine power to DC, and then con-

verting it back to an AC signal. The

frequency and voltage of the AC signal

outgoing to the AC motor can be ad-justed, enabling precise speed, torque,and positioning control.

Gearbox

The gearbox mounts directly to the maindrive motors at its input end, and re-duces motor input speed to a speedcompatible with raiseboring at its out-

put end.Most gearboxes use a planetary re-

duction system. This shares the load

among three planetary gears, reducingthe diameters of the individual gearsrequired, and allowing a more compact

drive train assembly.Gearbox reductions must include ra-

tios capable of providing high torqueand low speed for raise reaming, andhigh speed and low torque for pilot holedrilling. It is not uncommon to have amulti-speed gearbox with a var iable

speed motor.The output end of the gearbox is

attached by a splined connection to thefloating box, which connects it to the

Figure 3: Cross-sectional view of the drivehead.

Splinedconnection

Axialfloat

Floating box withpatented sphericaldesign and replaceablethreaded insert

Driveheadcapscrew

Swivelingaction

Figure 4: Pilot drilling and reaming.


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TALKING TECHNICALLY

16 RAISEBORING

drill st ring. The splined connection,while enabling the rotational power ofthe drive train assembly to be transmitted

into the drill string, also allows the floa-ting box to drift axially when threading

or unthreading drill string components.Axial free f loat permits the threa-

ding of the floating box to follow thethreading of the stationary drill string

component, greatly reducing the chancesof thread damage during connectionmake-up or breakout. Periodic heightadjustment of the drive train assembly

in relation to the drill string componentis necessary, which can be carried outby the operator.

Spl ined connect ion f loa t ingboxessupplied with newer raiseboring

machines are equipped with a spheri-

cal design patented by Atlas CopcoRobbins.

This provides a swivelling action in

addition to free float. This preventsbending, stresses from damaging thegearbox and accommodates slight drillstring misalignment.

The floating box can be housed in-ternally within the gearbox, or mountedto the output end of the gearbox as aseparate component. When mounted se-

parately from the gearbox, the assembly

housing the floating box is referred to as

the drivehead.The drivehead is connected to the

output end of the gearbox by spindlebolts or a single threaded capscrew. Ifa single capscrew is employed for thisconnection, drivehead installation/re-moval tools are required when instal-ling or removing the drivehead fromthe gearbox.

Hydraulic system assembly

The hydraulic system supplies hydrau-

lic power for raiseboring. This assemblycomprises the hydraulic power unit and

all interconnecting hose assemblies.The hydraulic power unit is on a

skid-mounted structure containing a hy-

draulic reservoir. These are used as mo-

unting platforms for the majority of thecomponents making up the hydraulicsystem. Included in these componentsare the motors and pumps used to po-wer the hydraulic system along withvarious valves, filters, and manifolds.

Lifting eyes are provided on thehydraulic power unit for hoisting andpositioning.

Design of individual hydraulic sy-stem assemblies varies according to thetype and size of machine. The servicemanual should be consulted for spe-cific hydraulic system setup, operation,

and maintenance procedures.

Lubrication system

The lubrication system assembly en-

sures proper delivery of lubricating oilto the high-speed bearings and otherselected components of the drive trainassembly gearbox. This assembly iscommonly made up of the lubricatingoil reservoir, with level gauge, thermo-

meter, and breather; pump drive motor;and lubricating oil pump, filter, heatexchanger, and flow meter.

Most Atlas Copco Robbins raise bo-ring machines employ the crosshead ofthe drive train assembly as the lubrica-

tion reservoir, and as the housing forthe lubrication pump drive motor and

Figure 5: Hydraulic power unit.

Figure 6: Electrical power unit.


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TALKING TECHNICALLY

RAISEBORING 17

pump. Some machines are designed with

the lubrication system reservoir and com-

ponents located separately from the der-rick assembly, usually to permit the der-rick to be tilted to bore raises at lowdip angles without affecting the levelof the lubrication oil reservoir and thefunctionality of the lubrication system.

Electrical system

The electrical system assembly com-prises the electrical power unit and allelectrical power and control cables.The electrical power unit consists of anenclosed cabinet containing the powerand control distribution hardware andcircuitry for the entire raiseboring sy-stem. Lifting eyes are provided on thiscabinet for hoisting and positioning.

Power and control cables are inclu-ded in the electrical system assembly.

Most of these cables are of the quick-coupler type, with all the plugs and

receptacles identified for ease in making

proper connections during systemsetup.

Because of varying site power sup-plies, and differences in main drivemotor systems and machine options, the

design of electrical system assembliescan be quite diverse from machine tomachine. The service manual suppliedwith each raiseboring machine should

be referenced for specific electrical sy-stem setup, operation, and maintenance

procedures.

Control console

The modern rig control system fromAtlas Copco features a Control Area Net-

work (CAN) for digital communicationbetween all modules connected to theBus wire.

The entire system features various

I/O (In/Out) modules for communi-cation with all machine sensors and

meters, a master module for computing

and processing of operational data, and

a display module for presentation ofcalculated data.

The I/O modules are positioned inthe thrust pack and the drive pack, aswell as on the derrick assembly. Thecomputing module is usually placed inthe drive pack, which is located in asafe, dry place for power supply and

convenience to major components.The display module is part of the

control panel, itself a robust assemblyenclosed in a waterproof envelope, spe-cially designed for outdoor and under-ground use.

Manufactured and delivered to over400 units since 1998, this proven, stan-dardized control system is modular, with

all major parts interchangeable withother similarly-controlled Atlas Copco

products.

Jan Forsberg

Figure 7: Robbins 73RH C with RCS control panel.


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18 RAISEBORING

Robbins 73RM-DC in TasmaniaHenty Gold Mine, owned by Gold Fields Tasmania Pty,

is located on the west coast of Tasmania, in the middle

of an environmental protection area with many re-

strictions. The mine needed more fresh air, and opted

for a raise bored ventilation shaft from surface.

Pilot and reamThe pilot hole was pre-drilled by a subcontractor in threestages to HQ 14 in using DTH equipment. A Robbins73RM-DC raiseborer was then employed by SkanskaRaiseboring of Sweden to develop the 689 m-long,2.44 m-diameter vertical ventilation shaft.

Crawler transporterSome ten 20 ft containers were used for transportationof the equipment to site.

The rig was mounted on an air powered crawler tran-sporter capable of 1.5 km/h and positioned on a specially-designed steel frame over a 10 m-deep concrete lined

pre-sink of 4.5 m-diameter. All drill tubes were inspected

with a magnetic particle inspection kit before the projectstarted.

One month of boringSkanska had three operators and one supervisor on site.Set up took seven days, and take down five days. Drillpipe was high strength, with 10 in outside diameter in 5ft lengths. Thread lubrication was Best o Life 3010 fromDallas, Texas, US. Pipe changes took 5-6 minutes, usinga side loading pipeloader and crane.

Boring took place over a 31-day period, during whichaverage penetration rate was more than 22 m/day. The2.44 m (8 ft) reamer was dressed with 14 cutters, 7 four-row and 7 five-row. The raiseborer developed thrust of100 - 280 t, the equivalent of 7-20 t on each cutter, witha torque of 350 and 7-8 rev/min. The drillstring wasstabilized using a stinger and two 13.625-in stabilizers,and no cutter changes were necessary during the boringoperation.

Satisfied customer

The machine gave close to 100% mechanical availability,delivering the raise in half the expected time, allowing

ventilation the equipment to be installed earlier thanexpected.

The mine had to bring forward extra resources formucking, in order to keep pace with the raise drilling.There were no accidents or incidents, and no reportableenvironmental impacts, such as oil leakage, and the cus-tomer expressed satisfaction with the project.

Side loading pipeloader in operation.

Robbins 73RM-DC under installation.

Reaming the Henty ventilation shaft.


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TALKING TECHNICALLY

RAISEBORING 19

Most popular modelWith 35 units delivered worldwide since 1980, the Rob-bins 73RM has become the most popular raiseboringmodel today. The 73RM is used to develop raises andshafts in the crucial 1.8 m to 3.1 m-diameter (6-10 ft)range.

The two medium-sized Robbins 73RM-VF raise bo-rers now at work developing ventilation shafts in the ar-duous conditions at Norilsk, Russia are an example. TheVariable Frequency drive governs the speed of the mainmotors, and consequently the speed of the pilot bit andthe reaming head, by means of frequency conversion ofmotor current.

Variable frequencyWith VF control, the machine and the drill string areautomatically protected from over-torque. Using full tor-que at minimum cur rent and low speed gives smoothstart-up and stop procedures at constant torque, withreaming performed in the 0 8 rev/min range (0 50 Hz),

and pilot hole drilling in the 0 30 rev/min range. At con-

stant power, reaming is performed in the 8 16 rev/minrange (50 100 Hz), and drilling in the 30 60 rev/minrange, where the torque drops as the speed increases.

Overcoming geologyThe ability to vary the reamer head speed is particularlybeneficial for operation under widely varying geologicalconditions, whether working in hard or soft rock, or solid to

fractured. Also, the reaming head speed can readily be adaptedto various reaming head diameters.

Variable speed cont rol was previously achieved byeither a hydraulic or DC electrical motor drive. Theadvantages of the Atlas Copco Robbins AC drive, whichis fully torque vector controlled, are superior efficiency,reliability and reduced operational costs.

In all, the final outcome is higher productivity andbetter cutter economy.

Variable frequency drive for Norilsk

One of two Robbins 73RM-VF machines delivered to Norilsk Mine, Russia..


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20 RAISEBORING

Expert knowledge

The course is based on the skills andexperience gained by key Atlas CopcoSecoroc personnel over many years and

conveys expert knowledge in the useof modern rock drilling products.

CBT Rock Drilling Tools version 4.0was released after six years of patientdevelopment. Computer based training

transfers knowledge about raiseboring

and drill str ing products, and their use,

in a simple and efficient way.Aided by 3-dimensional animations,

photographs, film sequences and inter-

active lessons, the training course ex-plains how the markets leading raiseboring and drill str ing products canincrease both productivity and profit.

With version 4.0, CBT now includestraining on all Atlas Copco Secorocproducts, with:

1. Three separate packages divided intoTophammer, DTH and Raiseboring.

2. Separate libraries for drilling equip-ment and applications in all packages;

3. Updated product training section ontophammer equipment i ncludingtroubleshooting, bit grinding and careand maintenance;

4. Product training section on in-the-

hole equipment including trouble-shooting, bit grinding and care and

maintenance;5. Product training section on consum-

ables for raiseboring equipment, in-

cluding care and maintenance;6. Focus tests on each lesson;

Computer based trainingfor raiseboringLatest versionAtlas Copco Secoroc recently in-troduced version 4.0 of its Com-puter-Based Training (CBT) pack-age as being of paramount im-portance in achieving the highestlevel of competence in rock dril-ling tools among distributors andcustomers, as well as its own salesforce. Correct understanding ofhow to choose, use and maintainthe rock drilling tools affects profi-

tability for all, and adds to com-petitiveness. Atlas Copco Seco-roc believes that the CBT packagefor rock drilling tools is the mostcomprehensive interactive train-ing tool available in the industrytoday.

Main menu. This is the first picture shown when you start the CBT. From this main

menu you can choose which of the courses you would like to enter.

Course menu. View picture for the course Raiseboring. Under the text Introduction you find two

buttons, Learning objectives will explain what you are expected to learn. Introduction will give

you an overview by running pictures and a speaker talking. Under Lessons you choose chapters.


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TALKING TECHNICALLY

RAISEBORING 21

7. a new section of product selection

exercises.

Complete training

The whole Secoroc CBT Rock DrillingTools package comprises approximately50 hours of lessons and tests. With arecommended maximum of four hours

of lectures per day, the total length of acomplete training course on rock dril-ling tools can be estimated at threeweeks.

CBT enables efficient training when-ever the need arises. For instance, a new

employee can start the learning process

right away, and learn about how the pro-duct is manufactured, its characteristics,wear limits and much more.

A modular structure enables usersto study lesson by lesson, or in a se-lective way at their own pace.

With personal computers, learning

can take place whenever and whereverthe individual chooses, including inthe field. The training package tea-ches you to find the right tool for any

given rock drilling application at any

time of the day. Similar to its experi-ence with CBT version 2.0, Atlas Copco

Secoroc has found good market accep-

tance of version 3.0, which has been ad-vising key customers and technicalschools on its use, as well as its ownsales team.

The new version of CBT 4.0 is ex-pected to even further cont ribute tothe added value in Atlas Copco Secoroc

sales service, inproving profitabilityand competitiveness for all involved in

raiseboring and rock drilling.

Bjrn Samuelsson

Chapter.In this section you choose the lesson you want. In the lower right

corner you find four buttons. X will finish the actual step. Number two will

take you back one step. The third button allows you to scroll through the course.

Lesson.There are three buttons for presentations. Video camera

button: running pictures and speaker text. Photo camera button: pictures

from more important or difficult parts. Text button: pictures and text.

Step player.When pressing the step player button you will find film

sequences or animations. At the end of every lesson you can also go through

a test, Focus test, to check your knowledge.

Product selection exercises.At the end you also have the possibility

to go through some real exercises, where you will have the background for a

specific rock excavation and from that choose the suitable equipment to do the job.


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22 RAISEBORING

Modifications

There are many different applicationsthat require horizontal or low angledrifts. Raiseboring is a non-explosivemethod, so the vibration effect on sur-rounding rock, and on buildings closeto the drill site, are kept to a minimum.Hydropower projects, urban sewerage

projects, and service drifts in mines area few examples where horizontal raise-boring has advantages over dr ill/blast

methods. The latter methods are noteven an option in the 0.7-1.2 m-diameter

range, because men and equipment are

simply not available to safely work such

small openings.The raiseboring method does not

change when the angle is lowered tohorizontal. However, transporting therock cuttings from the face becomesa challenge, because gravity does nothelp in the same way as for steeperholes. Hitting the target with the pilotbit also requires more skills than in a

vertical raiseboring application, be-cause of the downward pull of the drill

string.However, most types of raiseboring

machines can be modified to pull hori-

zontal and low angle raises. These modi-

fications generally include an alteredgearbox lubrication routing, a modi-fied base plate, and the addition of arear support for the guide columns.

Handling rock cuttings

A reamer used in a horizontal applica-tion employs scrapers to remove cut-tings from the rock face. These clean

Horizontal and low angle boring

New applicationsRaiseborers have been adapted tosome unusual situations wherehorizontal or low angle holes havebeen required. These have beenwell documented at projects whereraise bored holes were planned,such as at Venda Nova in Portu-gal. However, recent legislationfollowing a tunnel fire at Guadar-rama in Spain completely changesthe picture. At the Guadarramatwin railway tunnels, the TBMswere well ahead of the cross pas-sage development when a fire oc-

curred near the face. As a result,the fire crews were denied accessto the face along the parallel tun-nel, and had to stand off. All fu-ture twin tunnels in Spain will nowhave to develop cross passagesclose to the face. Because thesetunnels are mainly TBM- driven,and blasting would be risky to hu-gely expensive equipment, thecross passages will have to be de-veloped mechanically. Horizontalraiseboring is possibly the onlycurrently available alternative.

Low angle raiseboring.

Robbins raise drill in front of the face.


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RAISEBORING 23

the lowest point on the face prior toeach gauge cutter passing through, sothat the reamer is not forced upwards by

the cuttings. This will avoid unwantedbending stress in the drill string.

A large volume of water is also re-quired to keep the rock face clean andfree of cuttings. This can be introducedthrough the drill string, and either piped

from the back of the reamer, or throughholes drilled in the stem directed at the

gauge cutters.Additional flushing water can be

pumped from the machine to the faceon the outside of the drill string. A sea-ling system around the drill string, eq-uipped with an intake valve, is neces-sary with this method. This is similar

to the blooie system, which uses air asthe f lushing medium for pilot hole dril-ling. On raises with angles steeperthan 3 degrees from horizontal, largevolumes of flushing water, up to 3,000lit/min, should be sufficient to removethe cuttings.

Raises larger than 1.8 m-diametercan generally be mucked using a smallloader, while short holes can be muckedby hand. Water and scrapers are nee-ded to keep the rock face clean.

For smaller diameter raises close tohorizontal, mucking methods are more

innovative. The following methodshave been used successfully on recentprojects.

A pulley with steel cable is attached

on a swivel on the back of the reamer.The cable passes through the reamer,and a pair of air-powered winches isused alternately to pull out a scraper,which cleans the cuttings from the raise.Water and scrapers are needed to keepthe rock face clean.

Alternatively, a steel container is at-

tached to the back of the reamer with a

swivel. The scrapers on the reamer liftthe cuttings into the container, fromwhere a slurry pump and pipeline con-vey the cuttings out of the raise. Thismethod occasionally requires people in-

side the raise to extend pipe, route po-wer to the pump, and remove any over-size cuttings.

Another method is to use a non-rotating sealed plate pulled on a swivel

behind the reamer. A pipe is connected

to the sealed plate, and a pan is mountedjust below the pipe connector on thereamer side. The reamer scrapers liftthe cuttings onto the pan, and a mix-ture of air and water supplied throughthe drill string cleans the face. The in-

creased pressure inside the sealed areaensures that cuttings are blown out

through the pipe, which has to be ex-tended as reaming progresses. A cablethat attaches to the back of the sealedplate is used to winch the reamer outof the raise when necessary.

Horizontal piloting

The weight of the drill string causes de-

viation of the pilot hole in a horizon-tal application, so great care has to betaken throughout the piloting sequence.If the thrust is too high on the pilot bit,

it will divert the pilot hole upward. Iftoo low, it will divert the pilot holedownward.

Stabilizers installed along the pilothole will counteract some of the drill

string weight, as will a balanced amountof bailing medium, although too littlebail ing may cause the d ril l str ing tostick.

The accuracy of the pilot hole ismost affected by the machine set-upand collaring, for which an experienced

operator is a necessity. An accurate, but

more expensive and time consuming,

approach to a horizontal pilot hole isto drill it in three stages. First, a guidedcoredrilling machine drills an accurate

small-diameter hole. This is reamedby DTH to pilot hole size, following

Steel container collects cuttings behind the reamer.Collaring of the reamer showing the scrapers.


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24 RAISEBORING

which the raiseboring drill string is

installed.

Challenge at Venda Nova

A consortium of three Portuguese com-

panies, Somague, Moniz da Maia Serra& Fortunato (MSF) and Mota, was for-med to complete the civil works of the

Venda Nova project situated on the ri-ver Cavado in Ruives-Vieira do Minho,

in north Portugal as shown in the mapalongside.

The project required the drill/blastexcavation of 300,000 cu m of rock toprovide a 2.8 km inlet tunnel, a 1.4 kmdischarge tunnel, a powerhouse cavern,a 625 m-long ventilation tunnel, a1,210 m access tunnel, and a 130 mwater intake. There are also two raise-bored shafts of 415 m and 110 m.

The consortium chose Atlas Copcoequipment for the main operations usingRocket Boomer drill rigs, Secoroc rocktools, Swellex rock reinforcement, anda Robbins raiseborer.

Somague is the leading company inPortugal for drilling, mining and civil

works, and its relationship with AtlasCopco goes back some 40 years.

Rock conditions at the Venda Novasite are mainly favourable. The host rock

is granite, with some areas of schist and

zones with fractures and faults.One of the most challenging aspects

of the project was the development ofthe shorter of the two raise bored shafts.The 110 m escape and ventilation shafthas a decline of only 26 degrees, fromthe turbine hall to the existing ventila-

tion and escape system.Drillcon Iberia Lda, a subsidiary ofDrillcon AB of Sweden, used an AtlasCopco Robbins 73R raiseboring ma-chine to develop the shaft in fairly hardgranite of 170 MPa. The raiseborer wasmounted on a concrete platform in theescape tunnel, from where the pilot hole

was drilled down to the turbine hall.The tunnel was then reamed upwards,back to the escape tunnel.

A Secoroc RRL 3.5 m reamer wasflown in from Australia specially for theproject, as pictured below. The cuttersperformed perfectly, and the mucking

was very easy, using water pressure toassist with flushing the muck out during

reaming. A total of 18 new cutters wereused on the reamer: nine 5-row cutters,and nine 4-row cutters.

The deviation on the finished holewas 40 cm, which is less than 0.5 %.

Atlas Copco assisted the contractorswith every step of the raiseboring pro-cess, from training drillers on the Rob-

bins unit, to helping install new cutters

on the reamer. When the hole was fin-

ished, Atlas Copco personnel were onhand to demonstrate servicing of thereamer, maintenance of the cutters, andregreasing.

Drillcon have another two Robbinsraiseborers in Portugal, stationed atNeves-Corvo copper-zinc mine, where

they drill approximately 2,500 m/year.

The new Venda Nova plant and tun-

nel system came into operation in 2004to provide much needed generating ca-

pacity for the national grid. Venda Novawill also act as a pumped storage sta-tion serving its companion dam Para-dela further downstream. When elec-tricity demand is low, water that haspassed through the powerhouse for stor-age at Paradela can be pumped backthrough 4 km of tunnels to the VendaNova Lake, to provide extra power atpeak periods.

Mikael Bergman

Secoroc RRL 3.5 m reamer as supplied toVenda Nova in Portugal.

Checking the raiseborer drillstring in the 110 m shaft.

Location map for Venda Nova Dam worksite.

Venda Nova

Dam worksite


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RAISEBORING 25

Four decades of evolution

Raiseboring started in Germany, prima-rily in the Ruhr coalmines, where theypiloted from a lower level to a higherlevel and reamed down with successively

bigger reamers. The first machine to drill

down and ream up using the techniquethat is now known as conventional raise

drilling, was the Robbins 41R-1101 built

in 1962 for the Homer Wauseca Mine.The raise was 40 in-diameter and 200ft-long. The drill pipe was 5 in-diameter

and 4 ft-long, with oil drilling standardAPI tapered thread. This pipe was torq-

ued up so much during reaming that itbelled on the box ends and welded at the

shoulder, and each length had to be cutoff as it was removed. The pilot hole was

drilled using a Mission DTH hammer, and

Security designed and built the reamer.

Since those early days, some 600 raise-

boring machines have been sold world-

wide.The first Robbins 34R units were

made for Falconbridges Kidd Creekmine in Timmins, Ontario, Canada,

and have been in continuous use sincethey were commissioned.

The mine uses the machines to bore

1.2 m-diameter slot raises, and for down-

reaming 710 mm-diameter holes, which

are used for dumping backfill into empty

stopes.The Robbins 34R has a number of

special advantages: it is small, compact

and powerful; it can operate with as little

clearance as 3.4 m while drilling or rea-ming; and the hydraulic drive provides

variable speed control which helps theoperator to maximize machine per-formance in varying rock conditions.

In addition, with a number of auto-matic features, the Robbins 34R can be

operated by one person. These features

include a sensor that automatically shuts

down the boring cycle at the end of a

cylinder stroke, or at a pre-determinedlevel of torque.

Development of boxhole boring

Safe and efficientThe boxhole borer concept emer-ged in the early 1970s, and thecurrent models of dual-purposeraiseborers are a combination ofthe engineering skills and experi-ence gained since then. Boxholeboring has come a long way sincethe early machines employed onthe South African gold mines,and creditable advances are beingconsistently achieved at minesaround the world, without pilotholes and with minimum site pre-paration and setup time. Most of

the machines ever built are stillworking, releasing miners fromthe thankless task of manual rais-ing, to the benefit of all. Boxholeboring has contributed greatlyto improved safety undergroundwhile providing a far superiorraise at less cost.

Figure 1: The Robbins 34R raiseboring machine was the predecessor to the versatile Robbins 34R.


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26 RAISEBORING

Since those first two machines, theRobbins 34R torque and thrust has been

increased, and the model renamed the34RH-HT (High Thrust).It used to be necessary to bolt such

machines down securely on a concretepad, to cope with their high torque andthrust. Such pads were costly and time-

consuming to install, and have sincebeen replaced by a drilling platform that

uses leveling jacks combined with stinger

cylinders in the derrick columns, elimi-

nating the need for pads.

From raiseboring toboxholing

The advantages of raiseboring are: more

economical and much faster advancerates than drill/blast; more stable exca-

vation and considerably safer and better

work environment; smooth wall need-ing 300% less power for air ventilation;

cost/metre decreases as raise lengthincreases, allowing more flexibility inmine design and planning; and a signi-ficant reduction in labour requirements.

The common boxhole raise is an ore

pass raise driven from the haulage way

below to the ore body above. At thebottom of the raise, in the haulage, is achute base with guillotine gate to con-trol feeding of ore by gravity into haul-

age cars. The raise going up from thischute box or base is therefore knownas a boxhole.

The Robbins 34RH-HT can drill box-

holes, for which the machine is set upat the lower level and a full-diameterraise is bored upward. During boring,

Figure 2: The Robbins 34RH raiseboring machine has demonstrated its versatility at projects around the world for more than 25 years.

Figure 3: Boxhole boring can be carried out with or without a predrilled pilot hole, or in a combination of both.


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stabilizers are periodically added to the

drill string to reduce any oscillation and

bending stresses. The cuttings are car-ried by gravity down the hole, and de-flected from the machine for removal at

the lower level. Boxhole boring can becarried out with or without a predrilled

pilot hole, or in a combination of both,where a shorter pilot hole is predrilledto ensure straightness and orientation,followed by single pass/blind reamingand piloting in one step.

Boxhole borer development

Originally, the South African gold mines

utilized drill and blast techniques forthe 8-10 boxholes needed in each stope.

In the highly stressed footwall of these

very deep mines, this proved dangerous.In 1972, the West Driefontein Gold

Mine asked the Robbins Company and

Calweld Corporation to develop a box-hole borer. The raises were to be 90 m-

long, 5 ft-diameter, and from vertical to

60 degrees inclination. The result wasthe Robbins 51R, first produced in 1973,

featuring 24 in non-rotating drill string

and in-the-hole motor and drive system.

The thrust was 350,000 lb and the tor-que was 95,000 ft lb. The drill pipe was

4 ft-long with 3 radial fins for stabi-lization. The rig weighed only 28,000lbs and could be transported through a2 m x 2 m drift.

The 51R was later rebuilt as a 55R,which was the prototype of the 52R.The 52R was more compact, used 24 in-

diameter f langed pipe, had many hy-draulic and drive train improvements, a

built-in water spray, and non-rotary drill

string with in-hole cutterhead drive.Some 22 units of 52R with hydraulic and

electric drive were built, many of which

are still operating.In 1982, Robbins launched a project

to design a new machine, the 53R withderrick drive and rotary drill string. The

machine was designed so that site pre-paration work was limited to only a basic

pad. The reaming torque was 80,000lbs ft and thrust was 620,000 lbs.

The Robbins 53R was ready forSouth African gold mining, and the first

machine went to Vaal Reefs 8 Shaft in1984, where the first 42 m-long hole was

pre-piloted. All subsequent holes weredrilled blind, achieving penetration

rates of 2 m/hr to 2.5 m/hr with a 5 ft-diameter head, which in 25,000 psiquartzites was considered excellent. As

a result, the Robbins 53R became popu-

lar in the South African gold fields. The

muck chute was improved, and furtherwork was done on stabilizers.

Dual purpose machines

The Dual Purpose 34R is a low profile,

small diameter machine developed onthe basis of the 32R. The High ThrustHT version was developed in the 1980s

with 47,500 ft lbs torque and 289,000lbs thrust. It allows quick conversionfrom raiseborer to boxholer. It is alsoused around the world at places suchas: Brunswick Mine, Canada; ToyohaMine, Japan; Leinster Mine, Australia;

Western Metals (ARD), Australia; andEI Teniente Mine, Chile.

An important advantage with thedual-purpose machine is that bothboxhole boring and raiseboring can becarried out. The conversion betweendrilling modes is relatively quick andeasy. The 34R is turned upside downand a f loat box spring is added, whereas

Figure 4: The Robbins 51R raiseboring machine, first produced in 1973.

Figure 5: Robbins 53RH set up underground.


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28 RAISEBORING

the 53R has top and bottom chucks into

which the swivel is attached.Dual-purpose machines are espe-

cially useful in South African boxholesituations where mine layout allowsbox hol ing and conventional ra ise-bor ing from the same place, givingmultiple holes from one location.

Standardization on one machine type

results in signif icant savings in ma-chines, parts inventory, operator train-ing, maintenance training, proceduresand documentation.

Boxhole reaming

Initially, the reamer for boxhole boring

machines was installed overhead, a cum-

bersome procedure which also entailed

extra time and expense for the prepara-tion of each drilling site.

Accordingly, it was decided to extend

the width and depth of the machine toaccommodate the reamer and stabilizers.

The drill pipe wrenching system wasintegrated in the machines worktable,and was split into two halves, so that hy-

draulic cylinders opened it wide enough

to allow the passage of the reamer. This

feature increases the footprint of the ma-

chine, but does not increase its height,and produces a more functional system.

The remote controlled, hydraulicallyoperated slide-opening worktable ena-bles the entire drill string, includingboxhole stabilizers and reamer, to pass

through the worktable of the machine.Depending on model and frame widthof the 34RH-HT, reamers of diametersfrom 692 mm to 1,060 mm can passthrough the worktable.

Over the years, Atlas Copco engi-neers have designed many reamers,

both standard and specialized. Concern

about the possibility of ground squeez-ing during boxhole boring was over-come by fitting a set of gauge housings

and cutters, which are installed on theunderside of the reamer. In the event of

the ground squeezing during boringoperations, the RCC Duro cutters would

cut their way out as the reamer is with-

drawn from the completed boxhole.All Robbins 34R units are designed

so that the machines full torque andthrust are available in either the push-

ing or pulling mode. The 34RH-HT wasmodified to use stronger 10 in (254 mm)

drill pipe, to better stabilize the reamer,

and to transmit the full torque and thrust

of the machine.

Muck collection

To prevent the cuttings from covering the

machine as they fall down the bored raise,

a muck collector is installed betweenthe bored hole and the machine.

Atlas Copco have designed a muckcollector that connects to the head frame

of the Robbins 34RH HT, with exten-sion bars that can be adjusted to raiseor lower the muck collector by pushing

it with the drive head.The muck collector unit is f itted with

a rubber seal, which assists in contain-ing muck and dust. This is designed intwo halves, to be opened by remote-controlled hydraulic cylinders for thereamer and stabilizers to pass. It also fea-

tures a cone-shaped seal to clamp aroundthe drill pipe to prevent muck and water

from entering the drive box area of themachine.

The collector also incorporates amuck chute, which deflects the muckaway from the machine to the rear endin a 90-degree working range. Further-

more, this remote controlled and hy-draulically operated muck collector isfully integrated into the derrick assem-

bly, and remains on the machine, even

during transportation.The design of the 34RH-HT conti-

nues to evolve, as customer require-ments change, resulting in 360-degreedrilling, no concrete pad requirement,reamer and stabilizer installation under

the head frame, and an integral muckcollector.

Close cooperation between AtlasCopco engineers and customers is re-sulting in the continued development of

this most versatile raise drill.

Roberto Lopez

Figure 6: The remote controlled and hydraulically operated muck collector is fully integrated into the

derrick assembly, and remains on the machine even during transportation.


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Down reaming, one step

In the working sequence below, the rea-

mer needs to either pass through themachine work table or be assembled tothe drill string in a pit underneath theraiseborer. The raise is piloted

Drill string is pulled

The reamer is attached and collared

As the raise advances, stabilizers areattached to the drill string, usually in

a pre-determined pattern After breakthrough the drill string is

pulledThe diameter limitations on the above

method are set by the raiseborer thrustbearing load limit, the pilot hole size,and the chosen reamer connecting pro-

cedure as shown in Figure 2.

Down reaming, two ormore steps

The down reaming sequence, when theraise is done in several steps, is the same

as described above. When the first reamer

completes and is removed from theraise, the second, larger reamer is col-lared into the top of the hole. The front

of this reamer follows, and is stabilized

in the raise using drill string stabilizers

of the same diameter. Weight stacks have

historically been used on the reamer to

increase the thrust capacity in the down-

reaming system, as shown in Figure 3.

Down reaming

Increased safetyDown reaming is a type of raiseboring where a pilot hole is rea-med from the machine to a lowerlevel. This can be done in one orseveral steps to final diameter. Thecuttings are transported throughthe pilot hole to a lower level. Thismethod is mainly used for small-diameter slot-raises and backfilldrifts. Very occasionally the downreaming method is used for largediameter raises, usually in steps.Down reaming is more complexand more costly than raise rea-

ming due to the necessity to sta-bilize the reamer and drill stringwhen reaming. Removing cuttingsfrom the face requires more effortthan a standard raisebored shaft.Down reaming is mainly usedwhen the lower level is unsafe orif access to the lower level is fi-nancially not viable. One advan-tage for the down reaming me-thod is that all work is done atmachine level further increasingsafety over competing methods.

Figure 1: Part of the down reamer used on the San Giacomo project in Italy.

Figure 2: Down reaming, one step.

Pilot down Ream down


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Reamer, guide andstabilizer design

Down reamers should be equipped witha front guide. It should stabilize thereamer in the pilot hole while allowingthe cuttings to pass th rough into thepilot hole. Cuttings pass the front guidebetween the wear ribs. Some designslead the cuttings from the face through

the centre of the guide.In raise reaming, a f lat reamer pro-

file is best. This is not the case in downreaming. The cutters should be on anangle towards the pilot hole, so thatgravity can help the cuttings flow down-

wards. To prevent recutting, raises withlower angle than the reamer profileshould be avoided. If the down-reamed

hole has a lower angle than the reamerprof ile, than the cuttings have to bescraped, flushed or lifted into the pilothole, since the lowest point of the face is

not the pilot hole. The cuttings are flu-shed into the pilot hole by water pipeddown the drill string to the reamer, and

out to the reamer gauge. A rear guidering will further stabilize the reameraction, keeping carbide breakage to aminimum.

To centre and prevent side loading

of the drill string, rotating or non-rotating stabilizers are installed on evenspacing. The rotating stabilizer is of asimple design that works well in lowload applications. It is bolted onto thewrench flats on the drill string. The non-

rotating stabilizer consists of a specialdrill pipe with four arms mounted on a

bearing bushing. This design runs qui-

eter, and can be more heavily loaded.

Raiseboring machines to

be used for down reamingMost standard raiseboring machinesare equipped with a smaller bearing on

the pushing (pilot) side compared withthe main bearing on the pulling side(reaming).

Exceptions are the Atlas Copco Rob-

bins 34R H and 53RH Raiseborers.These machines are designed for raisereaming, down reaming and boxholeboring.

Roberto Lopez andMikael BergmanFigure 3: Down reaming, large diameter.


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RAISEBORING 31

Robbins 34RH set up for down reaming at Brunswick Mine.

Secoroc RDI 720 reamer in the hole.

Brunswick Mine has a partnership with Atlas Copco

Construction & Mining Canada that encourages

new product test ing and innovative change. For the

Brunswick operation, the change from 2-cutter to3-cutter RDI 720 down reamer in their slot reaming

programme has been a great success.

Falconbridge Limited Brunswick Mine has extracted and

processed ore from the world's largest underground zincmine for more than 40 years. Located in northern NewBrunswick, Canada, approximately 30 km southwest ofBathurst, the mine produces 3.6 million t/y of zinc, lead,copper and silver ore, and has produced 110 million t ofore to date.

The Brunswick orebody comprises massive sulphides,

with zinc, lead, copper and silver being the principal

metals produced. The host rocks and the mineralizationhave undergone four significant deformation events, re-

sulting in intense folding and faulting.Production is carried out on five main levels to a depth

of 1,125 m, and two shafts provide access. The mine em-ploys approximately 800 people.

Regular programmeFrom the first test r un three years ago, the Robbins34RH has down reamed 3,700 m of slot-raises. The minesregular programme is 3 to 4 slot raises a month. Thebench height is normally between 20 m and 45 m. The

slots are drilled on a slight angle from vertical.The down reaming working sequence is as follows: cleanthe drill site down to bare rock and pour a concretedrill pad at the site; erect, anchor and align the machineon the drill pad at the required angle; drill the 9 in-diameter pilot hole to break through, and retract thedrill str ing; install the down reamer through the drilltable, and down ream the hole to break through; attachrotating stabilizers to the wrench flats on the first rodabove the down reamer and on the wrench flats ofevery fifth rod; pull the dr ill string and down reamerout of the hole, once the hole is complete; and move theequipment to the next prepared drill site.

Viable alternativeDown reaming provides a viable alternative to conven-tional reaming when the lower level breakthrough siteaccess is restricted due to the mine planning sequence. AtBrunswick mine, as the advantages of the RDI 720 down

reamer were understood, a large number of the slot raisesthat were scheduled for conventional reaming were swit-ched to down reaming.

Unlike in conventional reaming, the complete down-reaming operation can be handled at machine level, andsecuring of the lower level is no longer necessary.


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This, of course, is a big advantage in underground benching,

sub level stoping, or any other underground mining methodwhere an open face needs to be created to safely blast the

initial excavation of a new production area.

Stable reamer actionThe RDI 720 down reamer has improved the speed ofthe operation in all aspects. Since the three-cutter designprovides more stable reaming action compared to its two-cutter counterpart, the reamer can be loaded higher, androtated faster, without transmitting excessive stress or

vibration back into the drill string. At Brunswick, thismore than doubled the penetration rate, while increasing

cutter life and reducing machine down time.With this higher productivity, the mine has reduced its

need for contracting additional raiseboring services from

external sources to keep up with the ongoing slot raisedemand.

Historical down reaming problems, low cutter life and

low penetration rate virtually disappear with the three-cutter design, and the customers save money by doingthe work themselves.

RDI 720 down reamer.

RDI 720.


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Innovation at work

BorPak gets its name from the expand-

able packer unit that absorbs the torqueand thrust of the rotating cutterhead.Cuttings gravitate down a guidance tube

and onto a conveyor. Operated from apanel outside the raise, BorPak impro-

ves worker safety and lowers labourcosts. A hydraulic power system advan-

ces the cutterhead, and steering is con-

tinuous, using a laser as a guide. Safetygrippers prevent the unit from slidingdown the raise between strokes or in theevent of power failure.

Atlas Copco engineers will workwith clients to design BorPak to spe-cific requirements of the job. The sy-stem can be fully automated, and iscapable of around-the-clock operation.

Site preparations are m

Education Under Ground Mining E Book 04

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