AECOM PowerPoint Template

AGS (HK)
1-day Seminar on Grouting and Deep Mixing
7 June 2014
Pre-Excavation Grouting in Hard Rock Tunnelling
By Knut F. Garshol
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
2
Why Ground Water Control?
Groundwater Movement in Rock
 Rock material is impermeable
 GW contained in discontinuities
 GW is migrating on conductive channels
Fault Zone
Massive
Rock
Jointed Rock
Conductivity contrast is an important factor in
GW control considerations
4
Effects of GW Ingress
 Surface Settlement
 Underground Safety
and Working Conditions
 Environmental Impact
5
Water in-rush at tunnel face
1 ton
6
Avoid such situations
“Small lake” became
smaller
Back to normal
14 km Gardermoen Tunnel,
Oslo, Norway
7
Experience from HATS Stage 1
 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
8
Manual handling of drill rods & packers
HATS Stage 1
9
Avoid Post Grouting!
HATS Stage 1
10
D&B Advantage: Drill Jumbo
HATS Stage 2A
Probe hole hitting 15 bar water channel
11
Benefits of GW-Control:
 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
12
Selection of Grout Mix
Purposes of Grouting
 Ground water control
 Ground stability improvement
 Sometimes: A combination of the above
 Requirements for success:
A suitable grout must be injected into the ground,
penetrating a sufficient ground volume to achieve
the targeted effects
14
Basic Grouting “Problem” in rock
15
Selection of Grout-Mix
 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
16
Traditional Technology – Disadvantages
 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
17
New Technology – Advantages
 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
18
Generally about Cement
 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
19
Marsh Funnel Viscosity
20
Mud Balance
21
Water-Cement Ratio
 W/C-ratio = 1.0 mix
Control by Mud Balance
22
Pressure Stability
23
Other important properties
 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)
24
Pre-Excavation Grouting
Execution Steps
Drill & Blast with PEG
After every 4th blast (typically)
Probe Ahead
Measure Water Inflow
Temporary Support
Pre-Excavation
Grouting
Scaling, Mucking
and Geological Mapping
Blasting
26
Execution Steps
 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
27
Grout Hole Pattern
Probe Holes
Grout Holes
Control Holes
 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
28
Tunnel CrossSection
Construction Method – Drill & Blast + PEG
Advance
approx. 4 m
29
29
Automatic Rod Handling
(EXAMPLE) Tamrock TRH rod-handling-system
Compared with manual
rod handling:
Double drilling output
AND
Improved Safety
Rod Magazine
30
Equipment Set-up - Simplified
Electronic Flow and
Pressure Recording
Packer
High-Pressure
Grout Pump
Colloidal
Mixer
31
Agitator
The Real Deal
Contract 24
AMV / Häny
Contract 23
Unigrout Atlas Copco
3 Pumps and 3 Grout Lines Each
32
Grouting Materials
 Microfine Cement
 Colloidal Silica
•Microfine Cement
•Pressure: 60-80 bar
•Volume 2000 L
•Colloidal Silica
•Pressure: 40 bar
•Volume 750 L
0.1
mm
Grouting Stop Criteria
MC
0.03 mm
CS
0.016 μm
Colloidal Silica
Microfine Cement
33
Colloidal Silica
OPC
0.1mm
Special Aspects of PEG
Safety of PEG works
Hydraulic
working
basket
Packers
secured by
chain
Disposable Packer
designed for 100 bar
35
Disposable Packers & Lances
36
Use of Standpipes in Poor Rock
37
Bag Packers in Poor Rock
38
Project Reference - HATS2A
Sub-Sea Sewage Conveyance – Hong Kong
Harbour Area Treatment Scheme – Stages 1 and 2A
Stonecutters
Island
Sai Ying Pun
North Point
Aberdeen
LEGEND
Outfall Tunnels (Completed)
HATS Stage 1 Sewage Tunnels (Completed)
HATS Stage 2A Sewage Tunnels
40
HATS 2A Overview
North Point
Contract 24
Sai Ying Pun
Contract 23
Victoria
Habour
Stonecutters
Island
41
Vertical shafts:
13
Total Tunnel Length: 20 km
Settlement Sensitive Reclaimed Land
North Point
Sai Ying Pun
HONG KONG ISLAND
Aberdeen
LEGEND
Coastline of Year 2005
HATS 2A Tunnels
42
Depth Below Sea Level
North Point to Aberdeen
Sai Ying Pun
North Point
Wan Chai East
Aberdeen
Cyberport
Central
Appx. 120 msl
Appx. 150 msl
Wah Fu
Sandy Bay
Appx. 70 msl
To Stonecutters Island
Crossing of Victoria Harbour
Stonecutters Island
Sai Ying Pun
Victoria Habour
LEGEND
Sea
Soil
Rock
43
Appx. 140 msl
Major Rock Types Encountered in HATS 2A Tunnels
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
Granitic Rock
• 66% of tunnel length
• Medium Grained Granite
• 50-percentile UCS = 180 MPa
Granite 66%
Granite/Tuff
Contact Zone
Granite
Tuff
Tuff 34%
Geological Map of Hong Kong (CEDD/GEO 2006)
44
Granite/Tuff Contact Zone
T
T
G
G
T
45
G
Distribution of Residual Ingress Limits
In granite
In tuff
50.0
Percent of Tunnel Length
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
5
15
30
L/min/100 m tunnel
46
50
Grouting Results
Residual Ingress to Excavated Tunnels
Rock Type
Granite
Tuff
Avg L/min/100 m
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
48
In Granite: Very Wet & Very Dry Sections
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
49
Probe Drilling in the Wet section
1200 L/min
15 bar pressure
50
Filled Open Joints
51
Filled Open Joints - Detail
20 MPa UCS
52
Practically Dry Tunnel 
13 September 2013
53
Summing Up HATS2A

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:



55
D&B excavation
Modern PEG technology
+ Re-measurable quantities for payment
CONCLUSION
CONCLUSION
In Hard Rock Tunnelling:
Technology for Ground Water Control by PEG
for Practically Dry Tunnels is currently available
Very Strict Ingress Limits will require:
Excavation by Drill and Blast
Micro Fine Cement
Colloidal Silica
57
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