Pre-Excavation Grouting in Hard Rock Tunnelling

AGS (HK) 1-day Seminar on Grouting and Deep Mixing

7 June 2014

By Knut F. Garshol

PresenterPresentation NotesGood Morning Everybody!

Your interest in the subject of PEG is much appreciated, so let us get started without wasting your time

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Headlines of this Presentation:

1. Why Ground Water Control?

2. Selection of Grout Mix

3. Pre-Excavation Grouting, Execution Steps

4. Special Aspects of PEG

5. Project Reference HATS 2A 1. Grouting Results 2. Summing Up HATS2A

6. CONCLUSION

Why Ground Water Control?

Rock material is impermeable

GW contained in discontinuities

GW is migrating on conductive channels

Groundwater Movement in Rock

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Jointed Rock

Massive Rock

Fault Zone

Conductivity contrast is an important factor in GW control considerations

PresenterPresentation NotesPlease Note: Rock is different to Soil!!

Conductive channels within joint plane or along crossing of joint planes.

Surface Settlement

Underground Safety and Working Conditions

Environmental Impact

Effects of GW Ingress

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Water in-rush at tunnel face

1 ton

PresenterPresentation NotesExamples of what can happen if probe drilling and PEG has NOT been executed!

The 1 ton is just a mental reminder that at 50 bar, if you want to hold back the water pressure in 51 mm diameter borehole, you need a force of about 1000 kp. This kind of hydrostatic pressure is not something to play with. It is seriously difficult and may be dangerous (500 m of water head!).

Avoid such situations

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Small lake became smaller

Back to normal

14 km Gardermoen Tunnel, Oslo, Norway

PresenterPresentation Notes14 km Gardermoen Tunnel, Oslo NorwayMajor media-circus Extensive Post-groutingSupplemented by permanent water re-charge

1st Joint Venture: Excavated 5% of 24.5 km Stopped by Water ingress Settled in Court New tender process

Stage 1 finished by the new Contractors, BUT. With substantial delays

Stage 2A: Drastically changed compared with Stage 1

Experience from HATS Stage 1

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Manual handling of drill rods & packers

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HATS Stage 1

Avoid Post Grouting!

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HATS Stage 1

D&B Advantage: Drill Jumbo

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HATS Stage 2A Probe hole hitting 15 bar water channel

Risk of major water in-rush practically eliminated

Gives basically dry working conditions in tunnels

Substantially improved stability in poor ground

Less water to pump to surface

Improved conditions for permanent lining works

Benefits of GW-Control:

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PresenterPresentation NotesIF PEG has to be done to prevent surface settlement, these Benefits are free BONUS

Selection of Grout Mix

Ground water control

Ground stability improvement

Sometimes: A combination of the above

Requirements for success:

Purposes of Grouting

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A suitable grout must be injected into the ground, penetrating a sufficient ground volume to achieve

the targeted effects

Basic Grouting Problem in rock

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Traditionally, locally available OPC w/c-ratio 3.0 to 1.0 mostly with Bentonite Unstable grout that needs "grout to refusal Low-quality and poor durability grout

Today, use of micro cement w/c-ratio 1.0 and lower Stable and thixotropic grouts (no bleeding) Bentonite replaced by admixtures

Selection of Grout-Mix

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High w/c-ratio gives lots of water to pump

High bleeding requires "pump to refusal" Gives extreme materials spreading, locally No cement enters finer cracks in first step, due to

clogging before pressure increase

Practically complicated (variation of w/c-ratio)

Conclusion: Time consuming

Traditional Technology Disadvantages

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Stable, low viscosity, fixed w/c-ratio grout Allows dual stop criteria for injection

Maximum pressure or maximum quantity per hole

Allows high output and pressure from start Gives simultaneous penetration of small and large cracks and openings

Conclusion: Time saved

New Technology Advantages

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Always the Primary grout material

Used as a suspension in water w/c-ratio typically between 0.45 1.5 (by weight)

Wide range of additives and admixtures

Wide range of cement types and properties

Permeation capability depends on: Particle size of the cement used Viscosity (and cohesion) of the suspension Pressure stability of the suspension

Generally about Cement

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Marsh Funnel Viscosity

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Mud Balance

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W/C-ratio = 1.0 mix

Water-Cement Ratio

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Control by Mud Balance

Pressure Stability

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Initial and final set time

Strength development

Final strength of injected grout

Stability and durability in the ground? 17 projects, 59 km of tunnel:

Average 37% ingress reduction (during 10 years)

Other important properties

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Pre-Excavation Grouting Execution Steps

Drill & Blast with PEG

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Probe Ahead

Blasting

Temporary Support

Scaling, Mucking and Geological Mapping

Measure Water Inflow

Pre-Excavation Grouting

After every 4th blast (typically)

Systematic Probe Drilling PEG if triggered

Minimum 5 m overlap (more in poor ground)

Grouting Stop Pressure 60-80 bar If not reached Stop on Quantity

Stable Micro Fine Cement Grout, Only

Colloidal Silica (where needed)

Overlap provides tight bulkhead for next probe drilling and PEG fan VERY important

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Execution Steps

Probe Holes Grout Holes Control Holes

Tunnel Cross-Section

Number of holes depend on tunnel span (1-1.5 m c/c).

Grout hole length (15 to 33 m). Lookout distance (5.5 m).

Schematic Layout of Drilling Pattern

Grout Hole Pattern

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Advance approx. 4 m

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Construction Method Drill & Blast + PEG

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Rod Magazine

(EXAMPLE) Tamrock TRH rod-handling-system

Automatic Rod Handling

Compared with manual rod handling:

Double drilling output

AND

Improved Safety

PresenterPresentation NotesAutomatic Rod Handling will double the drilling output AND improve work safety.

HATS2A Example: This is highly recommended when you have to drill more than 420 km of boreholes for GW control.

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Equipment Set-up - Simplified

Colloidal Mixer

Agitator

High-Pressure Grout Pump

Packer Electronic Flow and Pressure Recording

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Contract 23 Unigrout Atlas Copco

Contract 24 AMV / Hny

3 Pumps and 3 Grout Lines Each

The Real Deal

PresenterPresentation NotesHATS2A Example: For pumping of over 5000 tons of cement and large quantities of CS, proper equipment is crucial!

Microfine Cement Colloidal Silica

0.1

mm

OPC 0.1mm MC 0.03 mm

CS 0.016 m

Grouting Stop Criteria Microfine Cement

Pressure: 60-80 bar Volume 2000 L

Colloidal Silica Pressure: 40 bar Volume 750 L

Colloidal Silica

Microfine Cement Colloidal Silica

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Grouting Materials

PresenterPresentation NotesPrimary grout material is MFC NO OPC!

CS when further grouting is required and MFC cannot penetrate.

Special Aspects of PEG

Safety of PEG works

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Disposable Packer designed for 100 bar

Hydraulic working basket

Packers secured by

chain

Disposable Packers & Lances

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Use of Standpipes in Poor Rock

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Bag Packers in Poor Rock

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Project Reference - HATS2A

Sub-Sea Sewage Conveyance Hong Kong

PresenterPresentation NotesLet us start with the

Harbour Area Treatment Scheme Stages 1 and 2A

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North Point

Aberdeen

Sai Ying Pun

Stonecutters Island

LEGEND

Outfall Tunnels (Completed) HATS Stage 1 Sewage Tunnels (Completed) HATS Stage 2A Sewage Tunnels

PresenterPresentation NotesSlide shows Kowloon & HK Island: Densely populated and built up!

Stage 1 of the sewage Project consisted of 24.5 km of mostly TBM excavation and was completed over 10 years ago.

The yellow circle shows the TKO-area: Surface settlements encountered due to high GW ingress to the tunnel

Stage 1 experienced Several face collapses in shear zones, costing many months of delay. Primary reason: Hydraulic collapse or erosion.

Stage 2, the yellow line consists of 20 km of D&B excavation, currently 95% excavated.

HATS 2A Overview

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North Point

Stonecutters Island

Sai Ying Pun

Vertical shafts: 13 Total Tunnel Length: 20 km

Victoria Habour

Contract 23

Contract 24

PresenterPresentation NotesStage 2 is split in 2 Contracts as shown.

In addition to the 20 km of tunneling, there are 13 vertical shafts.

Settlement Sensitive Reclaimed Land

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North Point

Sai Ying Pun

LEGEND

Coastline of Year 2005 HATS 2A Tunnels

Aberdeen

HONG KONG ISLAND

PresenterPresentation NotesA lot of reclaimed land along the N-coast of HK-Island increases the risk of surface settlement and damage by GW drawdown.

Depth Below Sea Level

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North Point Wan Chai East Central

Sai Ying Pun Sandy Bay

Cyberport

Wah Fu

Aberdeen

Appx. 70 msl Appx. 120 msl

Appx. 150 msl To Stonecutters Island

North Point to Aberdeen

Crossing of Victoria Harbour

LEGEND Sea Soil Rock Appx. 140 msl

Victoria Habour

Stonecutters Island Sai Ying Pun

PresenterPresentation NotesWill show the rock types on next slide!

Major Rock Types Encountered in HATS 2A Tunnels

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Granitic Rock 66% of tunnel length Medium Grained Granite 50-percentile UCS = 180 MPa

Volcanic Rock 34% of tunnel length Predominantly Volcanic Coarse

Ash Crystal Tuff with subordinate Fine Ash Tuff

50-percentile UCS = 240 MPa Highly variable joint intensity

and orientation

Granite 66%

Tuff 34%

Geological Map of Hong Kong (CEDD/GEO 2006)

Granite/Tuff Contact Zone

Tuff

Granite

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Granite/Tuff Contact Zone

T T G

G

G T

Distribution of Residual Ingress Limits

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0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

5 15 30 50

L/min/100 m tunnel

Perc

ent o

f Tun

nel L

engt

hIn granite In tuff

PresenterPresentation NotesThis slide shows the 4 Residual Ingress Limits on the horizontal axisAndHow they are applied along the tunnelSPLIT on sections in Granite and Tuff

These limites were established based on numeric modelling and the risk level of surface settlement.

For Granite, 40% fall within the relatively relaxed limit of 50 L/min/100 m. This is because of the 4 km of low-risk (regarding settlement) tunneling crossing beneath Victoria Harbour.

The relative tunnel lengths in Granite and Tuff are almost the same for the 15 and 30 L/min/100 m limits.

The excavation length in Tuff within the strictest ingress limit is about 3X greater than for tunnel sections in granite.

As a result, tunnel sections in Tuff faced more demanding PEG-Works because of 1) Higher degree of rock jointing and 2) 3X longer section within strictest ingress limit.

Grouting Results

Residual Ingress to Excavated Tunnels

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Rock Type Granite Avg L/min/100 m

Tuff Avg L/min/100 m

Maximum Ingress Limit 30.2 16.9

Actual Residual overall ingress 6.5 7.5

Sections within limit (92%) 4.5 6.0

Sections failed (8%) 45.3 21.6

Average values Weighted against tunnel length

PresenterPresentation NotesFirst: The Measured ingress to excavated tunnel sections!

In Granite: Very Wet & Very Dry Sections

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LEGEND HATS 2A Alignment

Tunnel section 413 m long: Measured ingress from all 1st stage grout holes: = 9,200 L/min/100 m tunnel Measured after excavation: About 1.0 L/min/100 m (= 99.99% reduction) Cement Consumption: 1549 kg/m (= 5.7 X the granite average)

Tunnel section about 1500 m: Almost dry (hardly any PEG required) Cement Consumption < 50 kg/m

PresenterPresentation NotesIllustration of the wide range of conditions encountered!

Probe Drilling in the Wet section

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1200 L/min 15 bar pressure

PresenterPresentation NotesNote that excavation into the same channel without grouting => Would easily produce 5X more GW ingress (6 m3/min).

Filled Open Joints

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Filled Open Joints - Detail

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20 MPa UCS

PresenterPresentation NotesNote the brittle fracturing of the MFC grout illustrating the high compressive strength.

Early grout strength is Important for prevention of blow-out when excavating into treated area.

13 September 2013

Practically Dry Tunnel

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Summing Up HATS2A

Micro Fine Cement ONLY, supplemented by Colloidal Silica

Verification of result by Control Holes before further excavation

Tight face bulkhead is a Must especially in soft ground

27% of tunnel length required < 5 L/min/100 m tunnel

92% of excavated tunnels well below ingress limits

The Tuff required 78% more drilling ahead AND 3.7 X more Colloidal Silica than in Granite

Two Main Reasons for the Success: D&B excavation Modern PEG technology + Re-measurable quantities for payment

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Summing Up HATS2A

PresenterPresentation NotesBasis for Success Reasons Claim:

Stage 1: Several face collapses and months in delay, caused by problems of drilling necessary holes and outdated grouting technology. Settlement problems on surfaceStage 2: Zero face collapse problems. Ingress limits basically satisfied. Zero settlement problems on surface.

CONCLUSION

CONCLUSION

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Technology for Ground Water Control by PEG for Practically Dry Tunnels is currently available

In Hard Rock Tunnelling:

Very Strict Ingress Limits will require: Excavation by Drill and Blast

Micro Fine Cement Colloidal Silica

knut.garshol@gmail.com

Pre-Excavation Grouting in Hard Rock TunnellingHeadlines of this Presentation:Why Ground Water Control?Groundwater Movement in RockEffects of GW IngressWater in-rush at tunnel face Avoid such situationsExperience from HATS Stage 1Manual handling of drill rods & packersAvoid Post Grouting!D&B Advantage: Drill JumboBenefits of GW-Control:Selection of Grout MixPurposes of GroutingBasic Grouting Problem in rockSelection of Grout-MixTraditional Technology DisadvantagesNew Technology AdvantagesGenerally about CementMarsh Funnel ViscosityMud BalanceWater-Cement RatioPressure StabilityOther important propertiesPre-Excavation Grouting Execution Steps Drill & Blast with PEGExecution StepsGrout Hole PatternSlide Number 29Automatic Rod HandlingEquipment Set-up - SimplifiedThe Real DealGrouting MaterialsSpecial Aspects of PEGSafety of PEG worksDisposable Packers & LancesUse of Standpipes in Poor RockBag Packers in Poor RockProject Reference - HATS2AHarbour Area Treatment Scheme Stages 1 and 2AHATS 2A OverviewSettlement Sensitive Reclaimed LandDepth Below Sea LevelMajor Rock Types Encountered in HATS 2A TunnelsSlide Number 45Distribution of Residual Ingress LimitsGrouting ResultsResidual Ingress to Excavated TunnelsIn Granite: Very Wet & Very Dry SectionsProbe Drilling in the Wet sectionFilled Open JointsFilled Open Joints - DetailPractically Dry Tunnel Summing Up HATS2A Summing Up HATS2ACONCLUSIONCONCLUSIONSlide Number 58