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Planning and Development of

Underground Space in Rock Caverns

(CV6316)

Lecture 5 and 6

Cavern Stability Analysis and Rock Support Design

Lu Ming

Visiting Professor, NTU CEE

AY 2013-2014 Semester 2

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OUTLINE

1. Introduction2. Criteria for assessing cavern/tunnel stability

3. Methods of rock support

4. Analytical method for tunnel rock support design

5. Rock support design by empirical method - Rockmass classification systems

6. Rock support design by numerical methods

7. A commonly used process for cavern rock supportdesign

8. Design of rock cavern

9. Examples

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1. INTRODUCTION

Commonly used terms

Modes of cavern/tunnel failure

Factors affecting cavern stability Methods for cavern stability analysis

Methods for cavern rock support

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Rock Reinforcement and Rock Support

Rock reinforcement

Is used to improve the strength and/or deformational behaviour of rock

mass.

It generally consists of bolts or cables that are placed within the rock

mass in such a way that they provide confinement or restraint to

counteract loosening and movement of the rock blocks. In general, it is only fully effective in rock masses of moderate to high

strength.

Rock support

A load bearing structure installed on rock surface

The primary function of the support is to limit deformation of the rock

mass surrounding the tunnel

Is fully effective in failing weak ground

Generally consists of steel sets and shotcrete or concrete linings in

different combinations7

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Rock Reinforcement and Rock Support

Some support elements can be both reinforcement and

support, e.g. pre-tensioned rock bolts

Active support and Passive support: Acting load before and

after rock mass deforms

Rock Support, a commonly used term in engineering, refers

to Rock Reinforcement +Rock Support

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Temporary Support and Permanent Support

Temporary supportTo ensure a safe working environment before the next round

blasting

Must be applied immediately after the blasting

May be removed for installation of permanent support

Permanent supportTo meet the long term safety and quality requirements for

the entire lifetime (operation) of the underground facility

May be applied a certain distance behind the excavation

face Modern design: Temporary support serves as part of

permanent support

Primary and Secondary support

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Factors Affecting Cavern Stability

Strength and quality of intact rock Degree of jointing and character of

discontinuities

Overburden/In-situ rock stress Function requirements (internal pressure /

temperature)

Shape and dimensions

Water saturation

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Modes of Cavern/Tunnel Failure

Stress induced instabilityRock burst/spalling due to high stress for hard rock

Yielding of soft rock

Squeezing groundLocal instability at fracture/weakness zoon

Structure controlled instability

Wedge stability Rockfalls

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Methods for Cavern Stability Analysis and Rock

Support Design

Stress analysis using analytical solutions

Stress analysis by using physical modeling

(model tests) Stress analysis using numerical analysis

Empirical methods for rock support design

Basic concepts of modern rock support design(NATM/NMT)

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NATM (New Austrian Tunnelling Method)

For weak and squeezing ground. Structural supports are

needed

Basic principle: Take advantage of the bearing capacity of

weak rocks. Surrounding rock is transferred from loading body

into a load-carrying body. So only a reduced support is

needed to confine the unstable rock close to the tunnel.

Deformation of surrounding rock is allowed in a controlled

manner.

Support must have suitable load-deformation characteristics

and be applied at the right time

Design as you go or Design as you monitor approach:

systematic in-situ measurement of deformation and stresses

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NMT (Norwegian Method of Tunnelling)

For fast tunnel excavation at low cost in hard andjointed rock

Developed from experience gained in construction of5000 km tunnels in Norway

Is basically empirical, observationally based tunnelling. Contract system is based on the principle that the

contractor is paid for the amount of work whichactually has been performed and needed according tothe ground conditions encountered.

Flexible rock support adjusted to the actual rock massconditions plays an important role.

Risk-sharing contract system.

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2. CRITERIA FOR ASSESSING CAVERN/TUNNEL

STABILITY

Deformation

Stresses

Strains Yielding

Potential for rockfall

Failure of rock support elements

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Deformation monitoring

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3. METHODS OF ROCK SUPPORT

Rock bolts and cables Shotcrete (Sprayed Concrete)

Reinforced concrete lining

Steel plate lining

Precast concrete segments

Reinforced sprayed concrete ribs

Spiling bolts

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Rock Bolts and Cables

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Rock Bolts Functions of rock bolting

Bolt types End-anchored bolts

Fully grouted bolts

Strand cable

Swellex boltsfriction bolt

Split set

Yield bolt

Composite bolts (glassfibre)

AT bolts

Estimate of bolt length Application of rock bolts - Spot bolting , systematic bolting

and pre-bolting

Rock bolt model in UDEC and Phase2

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Rock bolts

A bar set in holes drilled into the rock to assist insupporting the tunnel roof or individual rockblocks that tend to fall into a tunnel.

Rock bolts maintain the stability of an opening by

suspending the dead weight of a slab from therock above by providing a normal pressure on therock surface to clamp discontinuities togetherand develop beam action by preventing key

blocks becoming loosened so that the strengthand integrity of the rock mass is maintained.

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Tunnel roof stability and rock bolting

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Function of rock bolt

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Suspension effect of roof bolting

TheLoad carried by each bolt P

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Beam building effect of roof bolting

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=

6

= 3

12

= ()

6

= ()3

12

B1: Strength of thecomposite beam

T1: Stiffness of thecomposite beam

B2: Strength of the boltedcomposite beam

T2: Stiffness of the boltedcomposite beam

B2=n2B1

T2

=n3T1

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Keying effect of roof bolting

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Bolt installed inclined to roof line

Bolt installed normal to roof line

b: bolt axial stress required to

stabilize the roof

p: Horizontal stress

: angle between the normal to the

fracture plane to the horizontal plane

: friction angle of the fracture plane

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Compression zone in roof created by bolt keying

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Bolt types

End-anchored bolt

Fully grouted bolt

Cable

Swellex

Split sets

Yielding bolts

Composite bolts

CT-Bolts

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End-anchored boltMechanically

anchored (expansion shell bolt)

Work well in hard rock,

not so well in soft or heavily jointed rock

Capacity drops to zero if anchor slips

Also resin anchored

bolts that work in

soft rock as well

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Fully grouted bolts - Grouted dowelPassive support: should be installed

close to face before

significant displacement takes place.

Support loading activated by rock

deformation.

Hole drilling

Grouting Bolt installation

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Fully grouted bolts with pre-tension

Anchored at end by grout or resin

Tensioning Grouting full length

Active reinforcement

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Cable bolts

High capacity

Flexible

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The cablebolt (oftenseven strand) arecement grouted intoborehole

Usually a 2-3 m longgrout anchor is formed

at the end of borehole The cablebolt is then

tensioned

Remaining part of theborehole is filled withgrout.

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Typical cablebolt installation for slope stabilization

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Swellex bolt (By Atlas Copco) 42 mm diameter tube

which is folded during

manufacture to create a

25 to 28 mm diameter

unit which is inserted

into a 32 to 39 mmdiameter hole

The bolt is activated by

injection of high

pressure water (30MPa) which inflates the

folded tube into intimate

contact with the walls of

the borehole.

Min Yielding load 200 kN

Min elongation 10%

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Swellex bolt (By Atlas Copco)

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Split set

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Slotted bolt inserted intoa slightly smallerborehole

Induced radial pressureanchors the system by

friction Typical data:

Yield load: 90 kN

Tube D: 33,39 and 46 mm

Hole D: 32, 35 and 41 mm

Main application: Miningindustry

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Lab test result on

load-deformationcharacteristics of

bolts by Stillborg

Testing set-up 2 high strength

concrete blocks

drilled hole

insertion of bolts

pull blocks apart

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Yielding rock bolts

The concept:Elastic-Perfect Plasticity

Application: rock condition where largedeformation occurs (mining industry) or dynamicloading

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Yield bolts

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YIELD-LOK yielding bolt

Yield load: 70-90kN (Dynamic load)120-135kN (Static load)

Elongation: 8%

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D-Bolt Newly developed at NTNU

Smooth steel bar with a number of anchors along its length.

Only fixed at the anchors positions.

The smooth sections between anchors can freely deform whensubjected to rock dilation.

Typical 3 or 4 sets of anchors.

Anchor

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Advantages of D-bolts

Dynamic performance of 22mm D-bolts: Maximum load: 250280 kN.

Maximum displacement: 145 - 163 mm per meter,

mean: 151 mm/ m

Maximum kinetic energy: 36 kJ per meter.

Strong as a rebar, but with a larger elongation tolerance

high energy absorption.

Reliable anchoring in the borehole due to the multi-point

anchors.

Combination of excellent Static and Dynamic properties

potential standard bolt.

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Yield load: 90 kN

Slide load: 80 kN

Elongation (static):

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FRP (Fibreglass Reinforced Polyester)

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FRP (Fibreglass Reinforced Polyester)

Composite RockboltsAdvantages

Corrosion resistance

Cuttability

All-Thread Rebar

High tensile strength

Flexibility Low weight

Anti-static conditioning

Anti-magnetic

High thermal isolation

No electrical conductivity

Disadvantages

Low elongation

Mainly used for temporary support

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CT-Bolts

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Tension test

http://www.ctbolt.com/objects/window_video.asp?RecordID=32

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Estimate of bolt length for systematic bolting

Non-pretensioned

L=1.4+0.184D (m)

D: Tunnel span

Pretensioned

L/a2

a3e

T 0.5-0.8K

a: bolt spacing

e: average joint spacing

T: Pretension force

K: Bolt capacity

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Estimate of bolt length for systematic bolting

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In meters

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Application of rock bolts

Spot bolting

Systematic bolting

Pre-bolting

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Spot bolting for stabilization of

individual rock blocks

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Systematic boltingbolting in a certain pattern,

usually normal to the excavation surface

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Prebolting - bolting ahead of excavation

usually for reinforcement of weakness zone

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Systematic bolting + shotcrete

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When Q-value < 1,

bolting as supportmeasure may not

be adequate on

its own. Rock mass

between the bolts

must be stabilized

by sprayed

concrete.

R kb lt M d l i UDEC

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Rockbolt Models in UDEC

Material model of bolt

Material model of grout

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Cable element properties:

(1) cb area cross section area of cable

(2) cb density mass density for cable

reinforcing [mass/volume]

(3) cb fstrain extensional failure strain

(default = 1010)

(4) cb spacing spacing of cables in out-of-

plane direction (default = 1.0)

(5) cb ycomp compressive yield force for

cable reinforcing (use positive value)

[force](6) cb yield tensile yield force for cable

reinforcing (use positive value) [force]

(7) cb ymod Youngs modulus for cable

reinforcing [stress]

(8) cb thexp thermal expansion coefficient

for cable

Grout properties:(1) cb kbond grout shear stiffness [force/unit

cable length/displacement]

(2) cb sbond grout shear strength [force/unit

cable length]

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Bolt Models in Phase2

End-anchored bolt

Fully bonded bolts

Plain Strand Cable Bolt

Shear Bolt (Swellex / Split Sets)

Tiebacks

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End-anchored Bolt

One dimensional deformable element. Tensile failure.

F=Kbu Kb=EA/L

u: Relative displacement between the two anchorage points

Residual capacity can be assigned (normally zero)

Pre-tension can be assigned

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Fully Bonded Bolt

A bolt is divided intoelements according toFE mesh

Bolt axial force

Fe=Keu Ke=EA/Le

Failure of elements intension

Yield and residualcapacity can beassigned Fyieldand Fres

Pre-tension possible

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Bolt-Joint Interaction

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Dowel force for shear resistance

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Limitation

Following potential failure modes are not

simulated

Failure of grout

Failure of bond between grout and rock

Failure of bond between grout and bolt

UDEC has a better model for fully bonded bolt

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Shotcrete (Sprayed Concrete)

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Shotcrete (Sprayed Concrete)

Functions of shotcrete

Strength of shotcrete

Fibre or mesh reinforcement

Thickness of shotcrete (min)

Application of shotcrete (wet and dry)

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Shotcrete creates a semi-stiff immediate

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Shotcrete creates a semi stiff immediate

lining on the excavated rock surface

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Functions of Shotcrete

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* Seal Surface

* Preserve Ground Strength

* Support of Individual Blocks

* Form a Structural Arch

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Seal SurfaceSeal Surface

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Barrier to Water Movement

Seal SurfaceSeal Surface

Seal on weak or expanding clays

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* Seal Surface

* Preserve Ground Streng th



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Preserve Ground StrengthPreserve Gro

und Strength

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Minimizes Loosening

Continuous Support

Smoothing of Surface Contours

Preserve Ground StrengthPreserve Ground Strength

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Preserve Ground StrengthPreserve Gro

und Strength

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Minimizes Loosening

Continuous Support

Smoothing of Surface Contours

Preserve Ground Strengthese e G ou d S e g

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* Seal Surface


* Suppo rt of Ind iv idual B locks


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Simple Support of Individual Blocks

SimpleSupport of Individual Blocks

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Acts as a Bridge

Between Joints

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* Seal Surface



*Form a Structu ral A rch

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S h f h

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Strength of shotcrete

C35 and C45

Tensile strength

High early strength is needed

Minimum thickness 80 mm, maximum up to

300 mm

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Mesh reinforced shotcrete

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Mesh reinforced shotcrete

Wire mesh is used to support small pieces ofloose rock or as reinforcement for shotcrete.Another layer of shotcrete is often applied tocover the mesh.

Two types of wire mesh are commonly used inunderground excavations: chainlink mesh andweldmesh. Chainlink mesh is commonly used forsupporting loose rock, whilst weldmesh is

commonly used for reinforcing shotcrete. Wire can be galvanized for corrosion protection.

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Welded mesh

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Welded mesh

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Chainlink mesh

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Chainlink mesh

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Fibre reinforced shotcrete

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Fibre reinforced shotcrete

Enhance compressive and flexural strength andsignificantly increase ductility (tensile strength)

Three types of fibres

Steel fibres (dosage 40-60kg/m

3

) Glass fibres (anti-corrosion)

Synthetic fibres (anti-corrosion, low cost, reducing

fibre rebound rate, easy logistics )

Control development of micro cracks

Reduce rebound in wet-mix spraying

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Energy absorption capacity of

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Energy absorption capacity of

fibre reinforced shotcrete (FRS)

An index for ductility or toughness of FRS Testing: it can be determined from a plate specimen

tested according to EN-14488-5. The plate test has been

designed to determine the absorbed energy from the

load/deformation curve. Classes:

Energy absorption

class

Energy absorption in Joules for

deflection up to 25 mm

Applied to rock

condition

E500 500 Sound

E700 700 Medium

E1000 1000 Poor

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During the test the panel (> 600600100 mm) is

supported on its four edges and a central point

load is applied through a contact surface of100100 mm.

The load deflection curve is recorded and the test

is continued until a deflection of 25 mm at thecentral point of the slab is reached.

From the load-deflection curve, a second curve is

generated resulting in a plot of the absorbedenergy (in Joules) versus the central deformation

or deflection.

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Energy absorption testing of fiber reinforced

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gy p g

sprayed concrete according to EN 14488-5

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L d d fl ti d E d fl ti

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Load-deflection and Energy-deflection curve

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Fibre types and properties

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Fibre types and properties

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CONSTITUENT MATERIALS

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CONSTITUENT MATERIALS

Cement

Aggregates

Additives

Silica fume (Microsilica)

Fly ash (Pulverized Fuel Ash or PFA)

Water

Chemical Admixtures

Plasticizers/superplasticizers

Hydration Control Admixture

Viscosity Modifying Admixtures (VMA)

Curing agents

Air Entraining Admixtures (AEA)

Accelerators

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Application of shotcrete

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Application of shotcrete

Dry-mix and Wet-mix methods Dry-mix sprayed concretesprayed concrete

in which most of the mixing water is added atthe nozzle.

Wet-mix sprayed concretesprayed concretein which all of the ingredients, including water,are mixed before introduction into the

delivery hose. Compressed air is introduced tothe material flow at the nozzle.

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General comparison dry-mix method and wet-mix method

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p y

Main Features Dry-Mix Method Wet-

Mix

Method

Equipment capital cost + -

Output 0 +

Equipment complexity + 0

Operating cost - +

Conveying distance + 0

Rebound - +

Dust - +

Use of fibers - +

Key: + advantage, 0 neutral, - disadvantage

* Wet-Mix method is the standard in Norway now.

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Support for various rock conditions suggested by Hoek

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Support for various rock conditions suggested by Hoek

101

From Support in Hard rock Underground Mines by Evert Hoek Published

in Underground Support Systems. Edited by J. Udd. (Montreal; Canadian

Institute of Mining and Metallurgy). Special Volume 35, 1987, pages 1-6.

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Reinforced Concrete Lining

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Design of Cast in Place Concrete Lining

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Design of Cast-in-Place Concrete Lining

Usually as the final lining in two pass liningsupport

Calculation of internal forces: moment and axial

force Tradition method of structure mechanics

By numerical method

Design of reinforcement with flexural (bending)calculation

Design of reinforcement with axial compression

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Structure Mechanics Method

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Structure Mechanics Method

As a frame

Loads: ground

pressure, water

pressure andother loads

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Numerical Method

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Numerical Method

Concrete lining assolid elements orbeam elements

Loads: in-situ rock

stress (includingvariation withdepth)

Water saturation

Interactionbetween rock andconcrete lining

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Moment and Axial Force

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Moment and Axial Force

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Reinforcement design - flexural and shear capacity

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bf

fAdfAM

c

ys

ysnf '85.02

19.0

df

VV

s

A

ys

csuv

dbfV cc '

17.0

From: ACI-318-08, Building Code Requirements for Structural

Concrete and Commentary

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As[mm2]: Area of longitudinal tension reinforcement

Av [mm2]: Required area of shear reinforcement

Vu[N]: Shear force acting on the section

Vc[N]: Nominal shear strength provided by concrete

s

: Shear reduction factor, assumed as 0.7

d [mm]: Distance from extreme compression fiber to centroid of longitudinal tension

reinforcement (typically the section height minus concrete cover)

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b [mm]: Width of the beam

s [mm]: Spacing of the shear reinforcement

fy[MPa]: Yielding strength of reinforcement

'

cf [MPa]: Compressive strength of concrete

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R i f t d i i l i

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Reinforcement designaxial compression

=

< . Small eccentricity:

compressionreinforcement can becalculated directly

Large eccentricity:

interactive diagramscan be used to findout the requiredreinforcement area

To check the compressive capacity of the concrete inthe compression zone

=

> .

M: moment

P: axial force

h: height of the beam

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Steel Plate Lining

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Used when tunnel is subject to

High internal water pressure (hydraulic jacking)

or

Extremely low temperature (high tensile stress)

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Precast Concrete Segments

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Can be used in either one-pass lining or two-

pass lining For two-pass lining precast concrete segments

are used as the initial lining, and the final

lining is the cast-in-place concrete Mostly used in soft ground TBM tunneling

Norwegian Inner Lining System in traffic

tunnels for water and frost protection

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Fire protection

of PE-form

covered by

sprayed concrete

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Reinforced Sprayed Concrete Rib

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Reinforced Sprayed Concrete Rib used

d k d

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in adverse rock conditions 1>Q>0.001

Fibre reinforced

sprayed concrete

Radial bolts

Rebars

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Reinforced Sprayed Concrete Rib used

i Qi d S b T l

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in Qingdao Subsea Tunnel

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Spiling Bolts

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A temporary rock support ahead of tunnel working

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A temporary rock support ahead of tunnel working

face in weakness / fracture zone. Small spacing.

It is very important to establish safe anchoring at therear end of the bolt prior to the next blast taking

place. The normal procedure is to use steel straps,

radial bolts, and fibre reinforced sprayed concrete as

back anchorage. There must be a radial bolt for each

spile.

May be combined with permanent support such as

shotcrete, reinforced shotcrete ribs and rockbolts Combined with reduced length of blast round

Optionally combined with concrete invert

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L- Length: 6 m

B -Spacing: 0.3(0.2-0.6) m

sl- distance

between 2 rows:2.3-3 m

V

recommendedangle: 10-15

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4. ANALYTICAL METHOD FOR TUNNEL SUPPORT

DESIGN

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DESIGN

Introductionthe concept

Convergence-confinement method

Ground Reaction Curve

Support Reaction Curve

An example

Summary

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Displacement of tunnel periphery develops as tunnel

advances

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advances

Elastic surface displacement of a circular tunnel of

radius riunder hydrostatic in-situ stress P0normalized with plain strain displacement P0ri/2G

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Support pressure and tunnel displacement

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Convergence-Confinement Method

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Point A: initial state

before work faceapproaches thesection

Point C: Work facehas passed

sufficiently awayfrom the sectionwithout any rocksupport

Point B: whereequilibriumbetween rock andsupport is reached

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Ground Reaction Curve

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Displacement (convergence) as a function ofsupport pressure

Also termed Ground Response Curve

Required Support Line Can be obtained from analytical solution or

numerical analysis

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GRC with M-C failure criterion by Brady and Brown

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Circular tunnel in M-C rock

Elastic-brittle stress-strainrelation

Hydrostatic in-situ rock stress

R=3m,p=10MPa,

=25kN/m3, G=600MPa,

f=2.0, =45, f=30,

c=2.414MPa

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GRC with H-B failure criterion by Carranza-Torrens and Fairhurst

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137

Analytical solution with H-B by Carranza-Torrens and Fairhurst

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Support Reaction Curve

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Also termed Available Support Line SupportReaction Line

Dependent upon types of support

Calculation methods have been developed byHoek and Brown for

Circular tunnel in hydrostatic stress field

Elastic-brittle stress-strain relation H-B failure criterion

139

Model

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140

S iff d i

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Support stiffness and maximum support

pressure are computed for Concrete or shotcrete lining

Blocked steel sets

End-anchored rock bolts or cables

Refer to Appendix C of Rock Mechanics for

Underground Mining by Brady and Brown

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C.2 Required support line calculation

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142

From Rock Mechanicsfor Underground

Mining by Brady and

Brown, Appendix C

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Assessment of support alternatives

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1. 8I23 steel sets at 1.5m centres with good blocking:

Adequate2. 8I23 steel sets at 1.5m centres with bad blocking:

Not adequate (roof)

3. 50mm thick shotcrete:

Sufficient stiffness and strength to stabilize the tunnel. But, stress

in shotcrete maybe too high and brittle failure may occur. Mesh and fibre

to increase tensile strength and ductility.4. 25mm diameter 3m long end-anchored bolts at 1.5m centres installed

within 3m from face:

Adequate support. But, safety margin for roof seems not enough.

May reduce bolt spacing at roof and increase spacing at walls and

floor.

5. 25mm diameter 3m long end-anchored bolts at 1.5m centres installedwithin 10m from face.

Roof collapse will occur due to late application of bolts.

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Summary

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Apply support at right time:

Too early: support load will be too high and support mayfail

Too late: tunnel may collapse due to large deformation

Mobilize strength of rock mass

Allow enough displacement to enable strength of rockmass to be mobilized

Without support the rock mass strength is fully mobilized,but tunnel may collapse due to excessive displacement

Load taken by rock and support Support stiffness: Different types of support have

different stiffness and different Support Reaction Curve

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5. ROCK SUPPORT DESIGN BY EMPIRICAL

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METHOD - ROCK MASS CLASSIFICATION SYSTEMS

Q-system

Use Q-value for rock support design

RMR system

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Q-system

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A given Q-value is an indication of given stabilitysituation with a given need for support

More than 1000 existing tunnels with permanent

support have been analyzed

Based on the analysis the relation between the

Q-value and permanent rock support is

documented

Such providing a guide for design of rock supportfor new tunnels

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Rock Mass Quality (Q)-system

by Barton and Grimstad

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by Barton and Grimstad

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Calculation of RQD from the number of joints per m3

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RQD=115-3.3JvJvis the number of joints per m

3

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151

In addition to the Q-value two other factors are

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In addition to the Q value two other factors aredecisive for support design:

tunnel dimensions and

safety consideration

Tunnel dimensions:

span width or height more support is needed with increasing dimensions

Safety consideration:

usage of the tunnel, or importance of the tunnel

safety

ESR (Excavation Support Ratio)

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= ()

153

ESR Estimate

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155

2013 Update (1)

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2013 Update (2)

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Use of the Diagram

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Notations

Sb: Spot bolting B: systematic bolting

Sfr: Fibre Reinforced Shotcrete

Sfr (EXXX): Fibre Reinforced Shotcrete with energy absorptionClass EXXX

CCA: Cast concrete lining RRS: Reinforced sprayed concrete ribs

Rock support is found for a given combination of Q-value and equivalent dimension

Bolt length: given at the right hand side, need to beincreased for unfavorable joint geometry

Bolt spacing

Minimum thickness requirement for shotcrete

158

Support of Walls

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159

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162

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1) Introduction

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The most popular tool for stability analysisand rock support design

Quantitative evaluation of cavern stability

Continuum approach and discontinuumapproaches

Input data play critical role

164

2) Continuum Approach

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Rock mass is taken as a continuous body Joints are taken into account by using reducedmaterial properties of rock mass

Significant discontinuities such as faults can bemodelled explicitly by joint elements

Strength of rock mass

Computing stresses and deformation

Compare stress with strength and evaluate theyielded zone

Strength of rock mass: H-B and M-C Input data:

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Input Parameters for M-C

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Frictional angle Cohesion c

Dilation angle dil

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Hoek-Brown Failure Criterion

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-2 0 2 4 6 8 103(MPa)

0

20

40

60

80

100

120

140

1

(MPa)

1> 2> 3compression positive

GSI=25, mi=10,mb=0.6866, s=0.0002404, ci=25

GSI=75, mi=30,mb=12.2845, s=0.06218, ci=80

Hard Rock

Soft Rock

2

331 cici sm

170

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171

Generalized H-B Failure Criterion

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a

cibci sm

3

31

172

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173

Input Parameters for H-B

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ci: Uniaxial compressive strength ofintact rock

mb: H-B parameter for rock mass

s: H-B parameter

a: H-B parameter

mdil: H-B parameter for rock mass

174

Strain Softening and Brittle Failure

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Residual Parameters

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For M-C

crand r

For H-Bmrand sr

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Basic input data

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Material properties of rock mass Deformability of rock mass

Strength of rock mass: H-B or M-C parameters

A commonly used process

Lab test for E-modulus of intact rock Lab test for UCS of intact rock

Field mapping for GSI index

Use software RocData in estimating deformability and H-Bstrength parameters

Use RocData to convert H-B to M-C parameters

In-situ rock stress

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Estimate of Rock Mass Parameters by Using RocData

Run RocData

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A tool foranalyzing rockproperties

Estimate of H-Bparameters

Converting H-Bto M-Cparameters

Rock propertydatabase

Analyzing labtest data

178

Conversion from H-B to M-C

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Other input data

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Groundwater

Dynamic analysis

Thermal analysis

Creep analysis

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Main Commercial Software

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ABAQUS

FLAC/FLAC3DDIANA

Phase2

182

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Cavern Stability Analysis and Rock

Support Design Using Phase2

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Introduction to Phase2 program

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Main features/functions Structure of Phase2

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Main Features of Phase2

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2D Finite Element software specially developedfor analysis for excavations and slopes in rockand soil.

It can be used for a wide range of engineeringprojects and includes tunnel support design,slope stability analysis, groundwater seepageand probabilistic analysis.

Plane strain or axisymmetric analysis

A low-end, practical, user-friendly and cost-effective software for engineers and students

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Program Structure

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Three modules MODEL(pre-processor)

To generate the model

COMPUTETo perform the computation

INTERPRET(post-processor)

For data visualization and interpretation ofthe computation results

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Model

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Modelling - Preprocessing

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Interactive geometry entry Grid/vertex/object snapping

Define boundariesexternal, material,

excavation, stage, joint, piezo, structuralinterface

Import/export in DXF format

Sequential staging of excavation and support

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Elements and Meshing

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3 or 6-noded triangles 4 or 8-noded quadrilaterals

One-click mesh generation

Graded, uniform or radial meshing Check/define mesh quality

Easy application of boundary conditions,material properties and loading

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Material Models for Rock Mass

Elastic

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Elastic

PlasticMohr-Coulomb

Hoek-Brown and Generalized Hoek-Brown

Cam-Clay and Modified Cam-Clay

Drucker-Prager

Discrete function

Staged material properties

Datum dependent properties Depth/Radial distance

For M-C: c, , E; For H-B: E Isotropic, transversely isotropic, orthotropic elastic models

Import from RocLab/RocData

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Loads

Constant or linearly distributed loads

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Constant or linearly distributed loads

Concentrated load Seismic load Pseudo-static seismic load (in x and y direction)

Seismic Force = Seismic Coefficient * Body Force (due to

gravity) Ponded water load

Load split "split" the field stress induced load between any stages

Use: to simulate 3D tunnel advance and delayedinstallation of rock support

Springs

191

Ponded water load

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In-situ Rock Stress

Far Field Stress

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Constant stress field

Gravity stress field

Multiple stress fields (customize per material) Load split per stage or material

193

Rock Support

Rock boltbolt types

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end anchoredfully bonded

cable bolts

Swellexsplit-set

tiebacks

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Rock Support

Linerliner types

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Beam (shotcrete)

Reinforced concrete

Geotextile

Cable truss

Composite liners

Reinforced concrete For concrete: concrete or shotcrete

For reinforcement: rebar, I-beam, lattice girder

Staged liner properties and staged support

installation

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Joints Individual joints

Joint network (joint sets)

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Joint network (joint sets)

Parallel Deterministic Parallel Statistical

Cross Jointed

Baecher

Veneziano

Voronoi

Joint mechanical model (yielding criteria)Mohr-Coulomb

Barton-Bandis

Hyperbolic slip Staged joint property

Datum dependent properties

196

Joint Networks

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Groundwater Seepage Analysis

Steady-state groundwater seepage analysis

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Steady state groundwater seepage analysis

Seepage analysis is (fully) integrated with thestress analysis (pore pressures computed fromthe groundwater analysis are automatically usedin the stress analysis to compute effective stress).

Following data can be computed and presented:Pore pressure, total head, flow lines, flow rate,discharge velocity, hydraulic gradient, effectivestress

Transient flow cannot be simulated (tunnel) Consolidation cannot be simulated

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Probabilistic Analysis

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Rosenblueth point estimate method Random variables - materials, joint properties,

field stress

Contour / error plots of statistical output

200

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Interpret

201

Interpret in Phase2

Interpretation and presentation of computing

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Interpretation and presentation of computing

result Contours of data for rock mass Stresses, Strains, displacements, strength factor

Yielding status of rock

Rock support Rock bolts: force and yielding

Shotcrete: force, moment and yielding

Others Deformed geometry, water pressure, etc.

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203

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204

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205

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Limitation of Phase2

Two dimensional (3D effect cannot be fully

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simulated) Cannot fully analyze following problemsGroundwater seepage

Seismic analysis

Cannot perform following types of analysisThermal analysis

Creep

Crack propagation

Strain-hardening/Strain-softeningLarge deformation (geometrical non-linearity)

207

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Run Phase2

208

3) Discontinuum Approach

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Discontinuities are explicitly included in themodel

Analyzing interaction of rock blocks

Simulating opening and sliding of joints Deformable and plastic rock blocks

Water flow along joints

Commonly used rock support

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Numerical Methods forDiscontinuous Modelling

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Distinct element method (DEM)

Discontinuous Deformation Analysis (DDA)

Numerical manifold method

Key block theory Boundary element method

Particle modelling

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A UDEC model for Gjvik cavern

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DISCONTINUOUS MODELLING

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Representative commercial code

UDEC (Universal Distinct Element Code)

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UDEC and 3DEC Major functions

Joint generation

Deformable and plastic blocks

Meshing in blocks

Different mechanics models for joints

Support modelling: Bolting and shotcreting

Fluid flow

Thermal analysis

Dynamics

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Input Data for Discontinuous Modelling

Mechanical input

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p

For blocks Strength parameters

Deformability parameters

For joints

Stiffness

Strength

Geometrical input

Joint distribution

Geometry of rock blocks

215

Mechanical Input for Discontinuous Modelling

Strength properties of discontinuities M C d l Di h

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M-C model:p

,r

, c,

Direct shear test

B-B model: JCS, JRC, r, Tilt tests, joint profiling test, Schmitt hammer

Difficulties: Representative joints, undisturbed samples

Stiffness properties of discontinuities

Constant?

sss

nnn

KF

KF

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Remarks on discontinuous modelling

Theoretically discontinuum approach is better

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y pp

suited to simulate jointed rock mass Acquisition of input data for discontinuous

modelling is much more complicated and expensivethan continuous modelling

Block models are best suited to slope stabilityproblems

Stability of underground works is dependent onjoint pattern around the opening which is almostimpossible to obtain exactly

217

ycontours

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218

Axial force on bolts

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219

Displacement vectors and axial force on shotcrete

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Displacement of rock blocks

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2D vs. 3D Analysis

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In most situations 2D analysis is sufficient fortunnel/cavern support design

3D analysis is needed for

Caverns L/D < 35

Intersection areas

Fractured/weakness zones

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Wedge Stability Analysis and Design ofBolting by Using Unwedge

Unwedge is a 3D stability analysis and

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Unwedgeis a 3D stability analysis andvisualization program for undergroundexcavations in rock containing intersectingstructural discontinuities.

Safety factors are calculated for potentially

unstable wedges and support requirements canbe modeled using various types of pattern andspot bolting and shotcrete.

Use Unwedgeto quickly create a model, perform

a safety factor analysis, place reinforcement andinterpret the results.

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An ExampleWedge analysis for aPower House Cavern

Three sets of discontinuities are detected in mapping

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Descriptions Foliation (F1) Joint (J1) Joint (J2)

Dip/dip direct. 25-35/340-020 70-75/180-200 80-86/270-295

Spacing (cm) 15 -70 20 -150 40 -120

Aperture (mm) 3 - open 3 - open 3 - open

Roughness Planar smooth Planar smoothUndulating-Planar

smooth

Filling Sericite/mica Quartz Quartz/ clay

Weathering Slightly weathered Slightly weathered Slightly -moderately

Persistence (m) > 20 3 -10 46

Water Dry Dry Dry

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Geometry and strength data for the three

joint sets used in the wedge analysis

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Joint set Dip () Dip direction

()

C

(MPa)

() JRC JCS

(ton/m2)

Joint set 1(J1)

70-75 (75)

180-200 (200)

0.90

20.83

6

7500

Joint set 2

(J2)

80-86 (87) 270-295 (274) 0.90 20.83 10 6100

Foliation (F1) 25-35 (22) 340-020 (359) 1.49 16.38 4 6800

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Combinations of joint orientation used in the analysis

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Case

Dip/Dip direction ()

Joint set 1

Joint set 2

Foliation

1 70/180 80/270 25/340

2 70/180 80/270 35/020

3 70/180 86/295 25/340

4 70/180 86/295 35/020

5 75/200 80/270 25/340

6 75/200 80/270 35/020

7 75/200 86/295 25/340

8

75/200

86/295

35/020

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Wedge view around cavern perimeter for joint

Combination 1

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End wedges for joint Combination 1

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Rock Support Design from Q-system

Roof

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Fully grouted 32 rock bolts, L = 8 m, in pattern 1.5 x 1.5 m

Fiber reinforced shotcrete 15 cm

Walls

Fully grouted 32 rock bolts, in pattern 1.5 x 1.5 m; L = 8 m for upper 10 m, L= 6 m for middle 10 m and L = 4 m for the rest lower part.

Fiber reinforced shotcrete 10 cm

The tensile capacity of the 32 rock bolts is taken as 300 kN and the shearstrength of the shotcrete is taken as 2 MPa.

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Rock support for combination 1

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231

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7. A COMMONLY USED CAVERN ROCK SUPPORTDESIGN PROCESS

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Use rock mass classification method, e.g. theQ-system, to estimate systematic rock support

Use FLAC/Phase2/UDEC to verify the rock

support Perform 3D analysis by using FLAC3D,

ABAQUS, DIANA, 3DEC, if needed

Check wedge stability by performing Unwedgeanalysis

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8. DESIGN OF ROCK CAVERN

Functional requirements:

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Temperature Pressure

Seismic loading

Volume

Traffic (inclination, AADT (Annual Average Daily Trafficvolume))

Water and frost protection (groundwater pressure)

Safety requirements (Manned or unmannded operation)

Environmental concerns

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8. DESIGN OF ROCK CAVERN

Cavern location

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Cavern orientation Orientation of in-situ rock stress

Orientation of major rock joints

Cavern depth

Cavern spacing

Cavern shape and dimensions

Maximum width/height

Simple shape

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Cavern orientation

For shallow caverns:

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Consider major jointset orientation

(perpendicular to

major joint sets)

For deep caverns:

Also consider the

orientation of the

major in-situ rock

stress (parallel to the

major horizontal in-situ stress)

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9. AN EXAMPLE

QINLING ZHONGNANSHAN ROAD TUNNEL

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Background

Design approach

In-situ rock stress measurement Rock support design

Numerical analysis

237

Project background

Worlds longest twin tube road tunnel (18 km)

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Two lanes each tube, speed limit 80 km/h Large overburden, up to 1640 m

High in-situ rock stresses

Mainly granitic gneiss

Construction started in March 2002, breakthroughDec 2004, open to traffic Jan 2007

Total cost 500 MSGD

Special lighting caverns for driving safety purpose

Minimum pillar width between tunnels only 8 m
http://maps.google.com.sg/maps?rlz=1T4GGHP_enSG457SG457&um=1&ie=UTF-8&gl=sg&daddr=Xi&

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China

Xian
http://maps.google.com.sg/maps?rlz=1T4GGHP_enSG457SG457&um=1&ie=UTF-8&gl=sg&daddr=Xi&http://maps.google.com.sg/maps?rlz=1T4GGHP_enSG457SG457&um=1&ie=UTF-8&gl=sg&daddr=Xi&

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240

Tunnel

Qinling Mountain

Range

Design approach

Rock stress measurements

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Empirical design

Cavern

Rock support

Numerical modelling control of empirical design 2D and 3D models

Excavation sequence design

Deformation monitoring Extensometer, fixed points

Tunnel and cavern outline

6 caverns, 3 in each tube

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242

Rock stress measurements at two locations

Xian

Ankang

Borehole 1 Borehole 2

Cavern geometryplan view

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243

Cavern geometryvertical cross section

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Excavation dimensions of tunnels and caverns

Special Lighting Cavern

Emergency Parking Zone

Standard Tunnel Section

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245

22.0 m

15.8 m

12.8 m

3.9m

3.9m

3.9m

6.6m

7.1m

9.0m

Core disking experienced in Borehole 2- 23 disks in 27 cm

A clear indication of extremely high stresses

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246

Result of 3-Dovercoringmeasurement

ORIENTATION OF MEAN PRINCIPAL STRESSES

N

SINTEF Rock and Soil mechanics

Project: 503350 kode: DISO 3.5nt Date: oct. 2005

2Hole 01

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247

Upper figure:Orientation

Lower figure:MagnitudeMAGNITUDE OF PRINCIPAL STRESSES

1

2

3

W E

S

1

3

0 5 10 15 20 25 30 35

PRINCIPAL STRESSES (MPa)

0

5

10

15

20

RELATIVEFREQUENCY

(%)

Tunnel

Final result of in-situ stress evaluation

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E1/W1 E2/W2 E3/W3

Vertical stress v[MPa] 10 40-45 15

Horizontal stress perpendicular to tunnel

axis h[MPa]15 25-30 15-20

Horizontal stress parallel to tunnel axis a[MPa]

15 25-30 15-20

Q-value is estimated as 4-28 basedon informatin provided by the clientand designers visual inspection

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Rock support design using Q-systemCaverns E1, W1, E3 and W3

Sprayed concrete, fibre reinforced with a thickness of

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150 mm. The sprayed concrete shall fulfil therequirements of C35 and have a minimum of 40 kgsteel fibres per m3, Dramix ZP305 or similar.

Systematic rock bolting in a 2.0 m pattern. The bolts

shall be 20 mm massive steel rebars, fully grouted andcomply with the quality requirements for rsta steelbolts with 3% elongation, yield load of 120 kN andfailure load of 150 kN, or similar.

Length of rock bolts shall be 7 m in the roof and 4 m inthe walls.

Rock support design using Q-systemCaverns E2 and W2

a) Excavation of original tunnels and temporary supportof the tunnels. The enlargement/broadening to reachh f ll ll d d

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the full cavern size will cause damaging anddemolishing of the temporary support

b) Slashing of the left hand side of the tunnel to reachfull height and full width of the area dedicated for the

emergency parking zone, constituting approximatelyhalf the full size of the cavern.

c) Before mucking out after the last blasting 3 m longholes shall be drilled in a 2x2 m pattern in the final

wall and roof areas as described in point b) above.The holes shall be equipped with protection toprevent sprayed concrete to clog the holes.

d) The newly excavated surface of the wall shall bemanually scaled to remove loose rock before beingsprayed with an initial layer of fibre-reinforcedshotcrete, building up a layer of 60 mm (mechanical

l h ll b ll d)

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scaling shall not be allowed).e) End-anchored rock bolts with length of 3m (polyester

cartridges shall be used for anchoring, not mechanicalanchors) shall be inserted in the pre-drilled holes inpoint c) above and the steel plates shall be mounted

outside the wet shotcrete. The nuts shall be tightenedonly loosely, so that the bolts are not pre-stressed.

f) The muck from the last blast round is removed andpoints d) and e) above are repeated. It is important that

the rock bolts and shotcrete are installed all the way tothe floor level.

g) Excavation of the right hand side of the tunnel to thefull height and width of the caverns, blast rounds shallbe parallel to the tunnel axis.

h) Installation of permanent rock support in theremaining part of the tunnel, i.e. the wall and roof onthe right hand side as was the last part to beexcavated. The installation of rock support shallf ll h d d ib d b i

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follow the same procedure as described above inpoints c), d), and e).

i) When the sprayed concrete has cured for 3-4 daysthe installation of permanent rock support may start.

10 m long steel bars shall be installed in a pattern of2x2 m to fill in between the existing rock bolts. Useend-anchored rock bolts with polyurethane cartridgeor other device which has a documented similarperformance.

j) Apply fibre-reinforced sprayed concrete to build upthe permanent shotcrete layer. The thickness of theshotcrete layer shall be 300 mm totally.

Overburden and in-situ rock stress

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E1/W1 E2/W2 E3/W3

Overburden [m] 400 1500 600

Vertical stress v[MPa] 10 40-45 15Horizontal stress perpendicular to

tunnel axis h[MPa]

15 25-30 15-20

Horizontal stress parallel to tunnel

axis a[MPa]15 25-30 15-20

Rock mechanics parameters of rock mass- defined in Standard for engineering classification of

rock mass of China

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Class Unit weight

(kN/m3)Friction angle

()Cohesionc (MPa)

Poissons ratio

I >26.5 >60 > 2.1 0.35

Rock mechanics parameters of the rock mass

Parameters E1/W1 E2/W2 E3/W3

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Parameters E1/W1 E2/W2 E3/W3

Rock mass classification index II- II+ II-

E [GPa] 20 29 20

0.25 0.215 0.25p[] 50 57 50r [] 40 47 40

cp [MPa] 1.5 1.9 1.5cr [MPa] 0.5 0.6 0.5

[] 10 10 10tp [MPa] 1.09 1.13 1.09tr: [MPa] 0.47 0.47 0.47

3-D numerical simulation with Flac3D

Goals of the 3-D analysis

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Overview of the rock mass responses to the

cavern excavations

Three dimensional effect along the tunnel axis

direction

E2-W2

E1/W1

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E2-W2 Numerical model

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Rockbolts and shotcreteFLAC3D 2.10

Step 20982 Model Perspective10:55:18 Tue Nov 29 2005

Center:X: 4 263e-001 Rotation:X: 30 000

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X: 4.263e-001Y: 2.851e+002Z: -1.450e+001

X: 30.000Y: 0.000Z: 190.000

Dist: 1.030e+003 Mag.: 3.05Ang.: 22.500

SEL GeometryMagfac = 0.000e+000

SEL Geometry

Magfac = 0.000e+000

E2-W2 resultYielding and displacementplan view

FLAC3D 2.10


Center:X: -3.359e+000

Rotation:X: 90.000

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X: 3.359e 000Y: 3.515e+002Z: 3.529e+000

X: 90.000Y: 0.000Z: 90.000

Dist: 1.030e+003 Mag.: 5.96Ang.: 22.500

Plane Origin:X: 1.500e+001Y: 3.500e+002Z: -2.000e+000

Plane Orientation:Dip: 0.000 DD: 0.000

Block StatePlane: on

Noneshear-n shear-pshear-n shear-p tension-pshear-pshear-p tension-p

DisplacementPlane: on Maximum = 3.355e-002 Linestyle

E2-W2 resultYieldingvertical cross section

FLAC3D 2.10


Center:

X: 3.513e+000

Rotation:

X: -0.000

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Y: 3.110e+002Z: 3.529e+000

Y: 0.000Z: -0.000

Dist : 1 .030e+003 Mag.: 5 .96Ang.: 22.500

Plane Origin:X: 1.500e+001Y: 3.440e+002Z: 0.000e+000

Plane Orientation: Dip: 90.000 DD: 0.000



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FLAC3D 2.10


Center:X: 1.159e+001

Rotation:X: 90.000

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Y: 3.457e+002Z: 2.964e+000

Y: 0.000Z: 270.000

Dist: 1.030e+003 Mag.: 5.96Ang.: 22.500





DisplacementPlane: on Maximum = 1.419e-002 Linestyle


FLAC3D 2.10


Center:X: 1 342e+000

Rotation:X: 0 000

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X: 1.342e+000Y: 2.995e+002Z: 2.186e-001

X: 0.000Y: 0.000Z: 20.000

Dist: 1.030e+003 Mag.: 11.6Ang.: 22.500



Block State Plane: on


Displacement Plane: on Maximum = 2.219e-002

Linestyle

E1-W1 resultMajor principal stress

FLAC3D 2.10


Center:

X: 1.159e+001Y: 3 457e+002

Rotation:

X: 90.000Y: 0 000

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Y: 3.457e+002Z: 2.964e+000

Y: 0.000Z: 270.000

Dist: 1.030e+003 Mag.: 5.96Ang.: 22.500



Contour of SMin Plane: on Magfac = 0.000e+000Gradient Calculation

-3.5355e+007 to -3.5000e+007-3.5000e+007 to -3.2500e+007-3.2500e+007 to -3.0000e+007-3.0000e+007 to -2.7500e+007-2.7500e+007 to -2.5000e+007-2.5000e+007 to -2.2500e+007-2.2500e+007 to -2.0000e+007-2.0000e+007 to -1.7500e+007

-1.7500e+007 to -1.5000e+007-1.5000e+007 to -1.2500e+007-1.2500e+007 to -1.0000e+007-1.0000e+007 to -7.5000e+006

E1-W1 resultBolt force

FLAC3D 2.10


Center:X 1 846 001

Rotation:X 0 000

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X: 1.846e+001Y: 3.457e+002Z: 2.964e+000

X: 0.000Y: 0.000Z: -0.000

Dist: 1.030e+003 Mag.: 9.31Ang.: 22.500



cable Axial ForceMagfac = 0.000e+000

tensioncompression

Maximum = 1.200e+005

cable Yield (tension)yielding nowyielded in past

Boundary Plane: onMagfac = 0.000e+000 Linestyle


FLAC3D 2.10


Center:X: 1.386e+000Y 3 423 +002

Rotation:X: 90.000Y 0 000

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Y: 3.423e+002Z: 7.458e+000

Y: 0.000Z: 90.000

Dist: 1.030e+003 Mag.: 4.77Ang.: 22.500





Displacement Plane: on Maximum = 2.279e-002 Linestyle


FLAC3D 2.10


Center:X: 1.386e+000Y 3 000 002

Rotation:X: 0.000Y 0 000

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Y: 3.000e+002Z: 5.497e+000

Y: 0.000Z: 0.000

Dist: 1.030e+003 Mag.: 7.45Ang.: 22.500





Displacement Plane: on Maximum = 3.524e-002

Linestyle

E3-W3 resultMajor principal stressFLAC3D 2.10


Center:X: 1.386e+000Y: 3 423e+002

Rotation:X: 90.000Y: 0 000

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Y: 3.423e+002Z: 7.458e+000

Y: 0.000Z: 90.000

Dist: 1.030e+003 Mag.: 4.77Ang.: 22.500



Contour of SMin Plane: on Magfac = 0.000e+000 Gradient Calculation

-3.7288e+007 to -3.5000e+007-3.5000e+007 to -3.2500e+007-3.2500e+007 to -3.0000e+007-3.0000e+007 to -2.7500e+007-2.7500e+007 to -2.5000e+007-2.5000e+007 to -2.2500e+007-2.2500e+007 to -2.0000e+007

-2.0000e+007 to -1.7500e+007-1.7500e+007 to -1.5000e+007-1.5000e+007 to -1.2500e+007-1.2500e+007 to -1.0000e+007

-1.0000e+007 to -7.5000e+006

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2-D numerical simulation with Phase2

Goals of the 2-D analysis

D il d d f h i i

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Detailed study of the entire construction

sequence at the most critical sections

Three dimensional effect is ignored

E2-W2

E1/W1

E3/W3

E1-W1 Numerical model

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Construction sequence

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E1-W1 Numerical model - constructionsequence

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-

- - -

-

- - -

-

- - -

-

- - -

-

- - -

E1-W1 Yielding - stage 3Total

Displacement

m

0.00e+000

2.40e-003

4.80e-003

7.20e-003

9.60e-003

30

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Shear

Tension

Shear

Tension

Both

1.20e-002

1.44e-002

1.68e-002

1.92e-002

-10

0

10

20

-40 -30 -20 -10 0 10 20 30


Displacement

m

0.00e+000

2.85e-003

5.70e-003

8.55e-003

1.14e-002

30

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Shear

Tension

Shear

Tension

Both

1.43e-002

1.71e-002

2.00e-002

2.28e-002

-10

0

10

20

-40 -30 -20 -10 0 10 20 30


Displacement

m

0.00e+000

4.50e-003

9.00e-0031.35e-002

1 80 002

30

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Shear

Tension

Shear

Tension

Both

1.80e-002

2.25e-002

2.70e-002

3.15e-002

3.60e-002

-10

0

10

20

-40 -30 -20 -10 0 10 20 30

E1-W1 Yielding - final stageTotal

Displacement

m

0.00e+000

4.50e-003

9.00e-003

1.35e-002

1.80e-002

2.25e-002

30

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Shear

Tension

Shear

Tension

Both

2.70e-002

3.15e-002

3.60e-002

-10

0

10

20

-40 -30 -20 -10 0 10 20 30

E1-W1 Major principal stressfinal stage

Sigma 1

MPa

0.00

3.00

6.00

9.00

12.0015.00

18 00

30

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Shear

Tension

Both

18.00

21.00

24.00

27.00

30.00

33.00

36.00

-10

0

10

20

-40 -30 -20 -10 0 10 20 30

E1-W1 Minor principal stressfinal stage

Sigma 3

MPa

-0.50

0.70

1.90

3.10

4.30 5.50

6 70

30

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Shear

Tension

Both

6.70

7.90

9.10

10.30

11.50

12.70

13.90

-10

0

10

20

-40 -30 -20 -10 0 10 20 30

E1-W1 Deformationfinal stage

Magnification factor 60

Total

Displacement

m

0.00e+000

3.00e-003

6.00e-003

9.00e-003

1.20e-002

1 50e-002

30

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Shear

Tension

Both

1.50e 002

1.80e-002

2.10e-002

2.40e-002

2.70e-002

3.00e-002

3.30e-002

3.60e-002

-10

0

10

20

-40 -30 -20 -10 0 10 20 30

E2-W2 Numerical model - construction sequence

Stage 2 Stage 4Stage 3

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Stage 5 Stage 7Stage 6

-

- - -

-

- - -

-

- - -

-

- - -

-

- - -

-

- - -

E2/W2 YieldingFinal stageTotal

Displacement

m

0.00e+000

1.20e-002

2.40e-002

3.60e-002

4.80e-002

30

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Shear

Tension

Shear

Tension

Both

6.00e-002

7.20e-002

8.40e-002

9.60e-002

-10

0

10

20

-30 -20 -10 0 10 20 30

E2/W2 Major principal stressFinal stageSigma 1

MPa

0.00

10.00

20.00

30.00

40.0050.00

60 00

30

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80.00

Shear

Tension

Both

60.00

70.00

80.00

90.00

100.00

110.00

120.00

-10

0

10

20

-30 -20 -10 0 10 20 30

E2/W2 Major principal stressFinal stage

Sigma 3

MPa

-1.50

1.50

4.50

7.50

10.5013.50

16 50

30

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13.50

Shear

Tension

Both

16.50

19.50

22.50

25.50

28.50

31.50

34.50

-10

0

10

20

-30 -20 -10 0 10 20 30

E2/W2 DeformationFinal stage


Total

Displacement

m

0.00e+000

8.00e-003

1.60e-002

2.40e-002

3.20e-002

4.00e-002

30

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Shear

Tension

Both

4.80e-002

5.60e-002

6.40e-002

7.20e-002

8.00e-002

8.80e-002

9.60e-002

-10

0

10

20

-30 -20 -10 0 10 20 30

E3-W3 Numerical model - construction sequence

Stage1 Stage 2

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Stage 3 Stage 4

-

- - -

-

- - -

-

- - -

-

- - -

E3/W3 YieldingFinal stageTotal

Displacement

m

0.00e+000

6.00e-003

1.20e-002

1.80e-002

2.40e-002

3 00 002

30

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Shear

Tension

Shear

Tension

Both

3.00e-002

3.60e-002

4.20e-002

4.80e-002

-10

0

10

20

-40 -30 -20 -10 0 10 20 30

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E3/W3 Major principal stressFinal stage

Sigma 3

MPa

-0.75

0.75

2.25

3.75

5.25

6 75

30

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6.00

Shear

TensionBoth

6.75

8.25

9.75

11.25

12.75

14.25

15.75

17.25

-10

0

10

20

-40 -30 -20 -10 0 10 20 30

E3/W3 DeformationFinal stage


Total

Displacement

m

0.00e+000

4.00e-003

8.00e-003

1.20e-002

1 60e-002

30

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1.60e-002

2.00e-002

2.40e-002

2.80e-002

3.20e-002

3.60e-002

4.00e-002

4.40e-002

4.80e-002

-10

0

10

20

-40 -30 -20 -10 0 10 20 30

Rock support summary- caverns E1, W1, E3 and W3

Excavation in 2 stages, first inner part and

then the outer part.

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then the outer part.

A layer of 15 cm shotcrete and 20 mm

diameter 7/4 m long fully grouted bolts in 2x2

m patterns installed right after eachexcavation stage.

This is the permanent support.

Rock support summary - caverns E2 and W2

Excavation in 2 stages, first inner part and then the

outer part.h d d d d h

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The support is divided to temporary support and thepermanent support

The temporary support consists of 6 cm shotcrete and

3 m long end-anchored bolts in 2x2 m patterns whichare installed right after each excavation stage.

The permanent support consists of 24 cm shotcreteand 20 mm diameter 10 m long end-anchored bolts in

2x2 m pattern which is installed 3-4 days after thetemporary support.

Some points from the support design

Rock stress measurements are important

2D numerical modelling may give conservative design

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Use 3D models for general design

2D models for detailed analysis and sequential design

Flexible support system is important when excavating

in high rock stress End anchored rock bolts

Flexible support consists of temporary and final support

Sequential excavation is important when excavating

caverns in high stressed rock mass

Special Lighting Cavern for

the Qinling Zhongnanshan Tunnel

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References

C. Carranza-Torres and C. Fairhurst Analysis of tunnel support requirements using

the convergence-confinement method and the Hoek-Brown rock failure criterion

www.ct-bolt.com

UDEC user manual
http://www.ct-bolt.com/http://www.ct-bolt.com/http://www.ct-bolt.com/http://www.ct-bolt.com/

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UDEC user manual

Phase2 online help

Unwedge online help

JunLu Luo A new rock bolt design criterion and knowledge-based expert system

for stratified roof phd thesis www.atlascopco.com
http://www.atlascopco.com/http://www.atlascopco.com/

Lecture 5 & 6(1)

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