rock tunnellingalan pengelly

7/30/2019 Rock tunnellingAlan Pengelly

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Cost-effective seepage control

and ground improvement inrock tunnelling with pre-

injections.

Alan Pengelly

Regional Manager, UGC Asia Pacific

20th

September 2008


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Contents

What is pre-injection?

Why Pre-inject?

Grout material types

Penetrability concept

Practical Aspects

Maneri Bhali Case Study

Arrow Head Case Study


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What is pre-injection?


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Why Pre-injection?

PrePre--injectioninjectionA proactive mindset!A proactive mindset!

In front of the tunnel face TunnelTunnel

1. Safety to reduce risk of tunnel collapse2. Environment drainage and

contamination of water table

3. Cost cheaper to deal with aboveproblems with low cost materials cementsthan with expensive chemicals


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Safety - Water inrush

They have serious waterproblems in the TBMtunnel.

Take a look at the

pictures, and you willunderstand why


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Environmental Impact


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Tunnel drainage effect

Very small water ingress to the tunnel =>

several meter pressure drop in the sand =>pore pressure loss and settlement in the clay

Functional requirements for injection

works


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Injection Material Types

Cement-based grouts Ordinary portland cement (OPC)

Microcementsystems

Mineral Grouts and Gels Colloidal silica

waterglass

Acrylates

Sophisticated two-componentsystems

Low viscosity

High reactivity

Taylored properties

Polyurethanes (PU)

One-componentsystemsreactingwith water

Two-component systems withtailored properties

Pre - injection Materials

Post - injection Materials


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Colloidal Silica Technology

Colloidal silica gel is a mineral grout, and isnot a chemical grout

It is a stable liquid containing single, sub-microscopic particles of silica oxide

To make it gel, a weak solution of salt water ismixed prior to pumping. The more salt wateradded, the faster the gel time

It is environmentally friendly and durable, as it issimply composed of quartz sand, water andsalt!

Having the consistency of water, it penetratessands and fine fissures very easily

It is extremely user-friendly as standard cement

grout equipment can be used and cleaned withwate


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Colloidal Silica Technology

Silica gel (hard aggregates)

Precipitated silica (grape clusters)

Silica fume (chain-like)

Colloidal silica (primary particles)

5 to 15 m

5 m

0.2m

0.015m


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Penetrability Concept

not related to w/c ratio !

< 5% bleedin 2hours

Marsh conetime < 35 s

D95


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0.0

2m

m OPC

50m

Rheocem65015m

Rheocem9009m

Silica fume 0.2m

MP3200.015m

Size matters! Grain size


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0.001 0.01 0.1 1 10 100

Colloidal silica MEYCO MP320

Urban tunneling require injection down towards 0,02 mm cracks

Ultrafine - Rheocem 900

Ultrafine - Rheocem 800

Microfine - Rheocem 650

Normal fine cement

Injection intocracks =3 x cementparticle size

Rock injection


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Grain size - penetration test Rheocem

Grout pumped from this side

90cmlongple

xitube


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< 5% bleedin 2hours


D95


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Stability - Bleed

Fine cementRheocem 650Rheocem650

Fine cement

bleed


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Setting time is a very important parameter to minimize the excavation cycle< 2 hours is ideal

SETTING TIME

< 5% bleedin 2hours


D95


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Water: 30 seconds

Rheocem 900 w/c = 1.0

Rheobuild 2000 PF, 2%

Runs through in 33 sec.

Viscosity - Marsh cone time


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Pro-active mindset:

pre-injection is an investment to avoid serious difficulties with wateringress and instable ground

A systematic process thatgives an opportunity to deal with groundinstability before we tunnel into it.

Drilling of probe holes in front of the tunnel face utlizing normaltunnelling equipment, injection when required ahead of the face

Utilization of relatively inexpensive injection materials, mainly basedon OPC and microcement

Injection with high pressure (> 50 bar)

Practical Aspects


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Typical length: 15 to 30 m

Typical spacing: 1 to 2 m

PrePre--injection is far more economical than post injection!injection is far more economical than post injection!

(10 to 50 times less expensive to stop water ingress)(10 to 50 times less expensive to stop water ingress)

Practical Aspects: low cost, less delays,

avoid the unexpected


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+ Water (w/c 1.0) + 1.5% Rheobuild 2000PF

MIXER PUMP

AGITATOR TANK

Packer

Use mix within 40 minutes!

Practical Aspects: Simple equipment.


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STEP 1:THE PACKER ISATTACHED TO THE INJ ECTION

LANCE AND PUSHED INTO THEHOLE

STEP 3:WHEN THE INJ ECTION OFTHE HOLE IS FINISHED, THE

VALVE CLOSES ITSELF. THEINJ ECTION LANCE ISDISCONNECTED BY SCREWINGBACK THE TIGHTENING LEVER,WHILE THE RUBBER SLEEVE ON

THE PACKER REMAINSEXPANDED.

STEP 2:THE PACKER IS

EXPANDED IN THE DRILLHOLEUSING THE TIGHTENING LEVER.

THE INJ ECTION CAN START.

Simple Packer Systems


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Hydro Electric Project.

Power House : 304 MW Project

HRT : 16 Km x 6 mtr Horse shoe

Owner : Uttaranchal Jal Vidyut Nigam Limited. (UJVNL)

Consultant : Irrigation Department, Govt. of Uttaranchal.

Contractor/s : M/s Hydel Constructions Pvt. Ltd.

Sub-contractor : M/s Shring Constructions Pvt. Ltd

Project started init ially in 1978, stopped in 1991 becauseof

a) collapse in the tunnel

b) lack of funds.

Restarted in 2002.

Indian Pre-Injection Case History

Maneri Bhali 7m dia head race tunnel


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The Clients Problem


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Conditions in original 20 year old tunnel


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Solution.

Construct a 150m by-pass tunnel to reconstruct thetunnel to correct profile and allow lining works to be doneto correct profile, whilst main tunnel lining and excavationcontinues

Use a Systematic Pre-injection technique to excavate

through the known fault and RBM zone to pass withoutcollapsing the face and minimizing water ingress

(original tunnel took 2 years to cross this zone)Combined use of Meyco Potenza, ribs and Shotcrete

to ensure face stability during excavation incombination with pre-injection


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Pre-injection Technique used :

Types of Injection materials used :

Microfine Cement - Rheocem 650 - 250T

Colloidal Silica Meyco MP 320 - 80T

PU Meyco 355 1K for sealing backflows 500kg

OPC was trialed but no penetration was achieved,despite water inflows continuing


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Two-stage pre-injection process chosen

with rapid hardening microcement andcolloidal silica

1. Rheocem

650

2. MEYCO MP320

colloidal silica


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Drill ing Sequence and pipe installation


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Packer Installation


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Results stable and substantially dry


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Conditions in original 20 year old tunnel


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Arrow Head East and West Tunnels


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Arrow Head East and West Water Supply

Tunnels

5.8m dia. Herrenknecht hydbrid Hard Rock TBM

Variable and unpredictable Rock Conditions Soft Rock


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Cost-effective pre-injections:

Water ingress reduction and groundimprovement in difficult rock


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Arrowhead Tunnels Project San Bernardino, CA

Pre-injections : drilling patterns

1,5Face

4Face


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Main Problems

Rock mass showed very unpredictable behavior

Large ultrafine cement takes (several thousands of lb) in one hole andnothing in adjacent regardless of water yield from a few gpmto 200gpm

Water and silt jets occurred. Several m3 of sand can come in beforepacker can be placed.

Cement picks up fine silt materials and creates filter cake blockingcracks and fissures.

Typically no cement intake except when they lost a lot of ground.

Porous rock mass if insufficiently grouted would lead face and peripherycollapse causing long stoppages for weeks.

Trials with Cement grouting with varying w/c ratios and stable groutswas proving ineffective in sealing.


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Solutions

Systematic rock grouting with cement to fill voids to replace washed

out materials. Extensive use of high penetrating colloidal silica gel with low

viscosity and particle size to waterproof the rock mass.

Down stage drilling process using simple bag packers to stabilize

drill holes for packer placement at correct location ahead of tunnelface.


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Plastic Bagpacker and borehole liner for

down stage drill ing process


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Bagpacker ready for grout expansion(Using quick setting mortar)


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Drillstring and Bagpacker(Typically down-stage drilling and grouting)


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Inflatable packer placed(Typically at 9 m depth)


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Typical solution in bad ground.

Double and triple cover grouting system.

Ring 3292

Water hit at 60ft with silt washout, 100 to 220gpm, pressure 250psi.

Injection 300,000lb cement to replace lost ground

19,000 gallons of colloidal silica to water proof the rock mass.

Injection sequence 22 days to complete, advance of 6 rings (30ft)

Ring 3298

Drill out to 140 ft, water down to 20gpm with 200psi

5000lb cement, 25,000 gallons of colloidal silica, complete after 6 days

Advance 30 ft

Ring 3304 - at start of original high volume and pressure water. Drill out to 140 ft, water down to 38gpm with 160 psi

26,000lb cement, 15,000 gallons of colloidal silica, complete after 5 days

Advance 30 ft and continue cylce until required


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Arrow head conclusions

Systematic use of pre-injection with appropriate materials allowedsuccessful excavation of TBM in poor ground conditions.

Requires highly competent and dedicated contractor.

Custom designed TBM required with effective probe drillingequipment designed fit for the purpose, 45 positions available for

drilling.

Use of appropriate colloidal silica mineral grout to penetrate finecracks and fissures and flowing ground where ultrafine micro-cement could not penetrate.

Many thanks forMany thanks for


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Many thanks forMany thanks for

your attentionyour attention

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