09/08/2012
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GeoSS 7 Aug 2012 温大志温大志温大志温大志 1
Deep Excavation and Tunnelling
Past Experience and Future Challenges
D Wen, BSc, PhD
PE, PE(Geo), AC(Geo), CEng, MICE, MIEAust, CPEng
2GeoSS 7 Aug 2012
• Review of Major Underground
Infrastructure Construction and
Singapore Geology
• Managing Ground Risk
• Managing Risk of Ground Movement
• Durability of Bored Tunnels
• Conclusions
Deep Excavation and TunnellingPast Experience and Future Challenges
3GeoSS 7 Aug 2012
MRT Network in Singapore
East
North-East
EWL
NSL
North
4GeoSS 7 Aug 2012
Major Underground Road Tunnels
CTE: North Tunnel: 0.7 km; South Tunnel: 1.7 km; Opened: 21 Sep 1991
Fort Canning Tunnel: 0.35 km; Opened 16 Jan 2007
KPE: Total tunnel length: 9km; Opened 26 Oct 2007 and 20 Sep 2008
Woodsville Interchange: Total tunnel length: 0.69km; Opened 28 Jan 2012
MCE Tunnel : 3.5km to be opened at end 2013
Singapore Underground Road System: underground road tunnels
North South Expressway Tunnel and Semi Tunnel : 12.3 km to be completed around 2020
5GeoSS 7 Aug 2012
Deep Tunnel Sewerage System
6GeoSS 7 Aug 2012
Cable Tunnels
• Cable Tunnels – Tuas and Seraya
• Gombas/Woodlands to Senoko
• Pasir Panjang Road
• Current 6 cable tunnel
projects under tender
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7GeoSS 7 Aug 2012
Caverns
• Rock Caverns in Jurong Formation
• Rock Caverns in Bukit Timah Granite Formation
8GeoSS 7 Aug 2012
Geological Process
Bukit Timah Granite
(Igneous Rock)
Jurong Formation
(Sedimentary Rock)
GI/GII/GIII
GIV
GV
M
F / E
S4
FCBBOA
In-filled Valleys Deep weathering of granite
9GeoSS 7 Aug 2012
Newton
Outram Park
Serangoon
Dhoby Ghaut
Kallang Formation
Old Alluvium
Jurong Formation Gombak Norite
Bukit Timah
Granite
Scale :
Boon Lay
Reclamation
Mandai Punggol
Geological Map
-2 0 1 2 4 (Km)
10GeoSS 7 Aug 2012
• Review of Major Underground
Infrastructure Construction and
Singapore Geology
• Managing Ground Risk
• Managing Risk of Ground Movement
• Durability of Bored Tunnels
• Conclusions
Deep Excavation and TunnellingPast Experience and Future Challenges
11GeoSS 7 Aug 2012
Site Investigation
• To provide sufficient ground and
ground water data � for a proper description of essential ground
properties / behaviour to plan the most appropriate construction method; and
� for a reliable assessment of characteristic
values of ground parameters to achieve a safe and cost-effective design
12GeoSS 7 Aug 201212
SITE INVESTIGATION PHASES
• Continuous process for entire duration of project
• Phased approach
�Desk study
�Preliminary
�Detailed
�SI during construction
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13GeoSS 7 Aug 201213
DESK STUDY
• Geological archives/maps
• Previous site investigations at the area
• Historical land use survey
• Published case histories
14GeoSS 7 Aug 2012
Increased Effects of Site Investigation
Co
st o
f R
isk a
nd
SI E
ffo
rts
Cost of RiskCost of SI
Combined Cost
Optimum Effort
COST OF SITE INVESTIGATION
15GeoSS 7 Aug 2012
Source: Westland, J.R. et al (1998) Managing subsurface risk for Toronto’s rapid transit expansion program. Proc. North American Tunnelling. I. Ozdemir ed. Balkema.
COST OF SITE INVESTIGATION
16GeoSS 7 Aug 2012
• USNCTT (1984): 3% of predicted
construction cost
• USNCTT: 1.5m borehole for every I m of
tunnel
• Hong Kong – major projects – around 1%
Source: United States National Committee on Tunnelling Technology. (1984) Geotechnical site investigations for underground projects. National Academy Press.
COST OF SITE INVESTIGATION
17GeoSS 7 Aug 2012
COST OF SITE INVESTIGATION
• NEL: Average borehole spacing 36.5m
• NEL SI Cost to Civil Cost: 0.216%
• DTL3: Average spacing 17.5m
• DTL3 SI Cost to Civil Cost: 0.283%
18GeoSS 7 Aug 2012
Geotechnical Geotechnical
Interpretative Interpretative Baseline Report Baseline Report
(GIBR)(GIBR)
Nature, form, composition, properties Nature, form, composition, properties and structure of the ground and and structure of the ground and groundwater, artificial obstructionsgroundwater, artificial obstructions
Site Investigation: field Site Investigation: field
and laboratory worksand laboratory works
Geotechnical Factual Geotechnical Factual
Report (GFR)Report (GFR)
GeotechnicalGeotechnical
InterpretativeInterpretativeReportReport (GIR)(GIR)
Contains the factual data from site Contains the factual data from site investigation & laboratory testsinvestigation & laboratory tests
Interpreted ground conditions for design, Interpreted ground conditions for design, e.g. design sections, design parameters e.g. design sections, design parameters
Site Investigation ReportSite Investigation Report
From DTL
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19GeoSS 7 Aug 2012
GIBR
• To explicitly share the commercial risk
with contractors
� Set “Baseline” for commercial purpose
� Set minimum requirements for design
20GeoSS 7 Aug 2012
Challenges
Tunnel Alignment
21GeoSS 7 Aug 2012
• To have more boreholes – practical
problems
• To carry out geophysical survey
Challenges
22GeoSS 7 Aug 2012
22
• Commonly used methods
� Electrical resistivity
� Seismic refraction
� Seismic reflection
� Surface wave method
� Geo-tomography
Geophysical Survey
23GeoSS 7 Aug 2012
Geophysical Survey
• Methods commonly used for soil / rock
interface identification
• Results are
� indirect interpretation of ground condition
� influenced by many factors, e.g. utilities,
traffic noise
24GeoSS 7 Aug 2012
Soil / Rock Interface – Accuracy ?
Interpreted Profile of Surface Wave Velocity
Interpreted Rock Profile
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25GeoSS 7 Aug 2012
Soil / Rock Interface – Accuracy ?
ABH18
ABH21
ABH26 FILL
F1
GV & GVI
GIII & GII
FILLF1
GV & GVI
GII & GIGIII, GII & G1
FILLF2EF1F2F1
GVI & GV
26GeoSS 7 Aug 2012
Detection of Pile Depth – Accuracy?
Estimated Pile Penetration: 21~22m (or) 26~27 m
27GeoSS 7 Aug 2012
Detection of Pile Depth – Accuracy?
28GeoSS 7 Aug 2012
Challenges
• More efficient and accurate methods are
required to determine
� rock levels
� depth of piles
to minimise risk of underground
construction in urban areas
29GeoSS 7 Aug 2012
• Review of Major Underground
Infrastructure Construction and
Singapore Geology
• Managing Ground Risk
• Managing Risk of Ground Movement
• Durability of Bored Tunnels
• Conclusions
Deep Excavation and TunnellingPast Experience and Future Challenges
30GeoSS 7 Aug 2012
Managing Risk of Ground Movement
• Ground Stability
� Ultimate limit state to prevent collapse
• Ground Movement
� Serviceability limit state to prevent damage to adjacent properties /
underground utilities
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31GeoSS 7 Aug 2012
Managing Risk of Ground Movement Deep Excavation
Cut Slope at Tanjong Pagar Station: Original Design vs
Revised Design
Cut Slope at Orchard Station: Original Design vs Revised
Design
After Hulme, Potter & Shirlaw (1986) 32GeoSS 7 Aug 2012
After Hulme, Potter & Shirlaw (1986)
Managing Risk of Ground Movement Deep Excavation
33GeoSS 7 Aug 2012
Singapore Art Museum
Cathedral of the Good Shepherd
Bras Basah Rd
B1 Level
B2 Level
B3 Level
B4 Level
B5 Level
Connection SMU
Reflection Pool
Managing Risk of Ground Movement Deep Excavation
34GeoSS 7 Aug 2012
Managing Risk of Ground Movement Deep Excavation
35GeoSS 7 Aug 2012
Managing Risk of Ground Movement Deep Excavation
After Goh (2008)
36GeoSS 7 Aug 2012
Deep Excavations in Soft Clay without Ground Treatment
Deep Excavations in Soft Clay with Ground Treatment
Ground Treatment
Managing Risk of Ground Movement Challenges in Urban Environment
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37GeoSS 7 Aug 2012
Jet Grouting System
GroutAirGrout
Air
Grout
AirWater
Air
Single tube jet grouting
system
Triple tube jet grouting
system
Double tube jet grouting
system
38GeoSS 7 Aug 2012
0
20
40
60
80
100
120
140
160
0 10 20 30 40
Wall
defl
ec
tio
n, m
m
Depth from ground surface to hard strata, m
Jet Grouted slab, 800mm wall
TREND LINE, 1m to 1.2m DIAPHRAGMWALLS, NO JET GROUT
Effectiveness of Jet Grout in Marine Clay
After Shirlaw, Tan & Waong (2005)
39GeoSS 7 Aug 2012
Deep Soil Mixing (DSM) / Deep Cement Mixing (DCM)
40GeoSS 7 Aug 2012
Hybrid ground treatment Deep soil mixing + Jet grouting
(Eg RASJET)
2.8m diameter columns achieved below formation
level for C828 Nicoll Highway Station (φ1.6m internal column by mixing blades)
41GeoSS 7 Aug 2012
Cross Walls
Circle Line Paya Lebar Station – Use of Cross Walls
Masjid Wak Tanjong
Use of Cross Walls
42GeoSS 7 Aug 2012
SOIL IMPROVEMENT WORKS by Cross Walls (lean concrete wall)
115E/W
DIAPHRAGM WALL
STRUT S2a
116E/W
114E/W
EWL VIADUCTEXISTING PIERS TO BE UNDERPINNED
EXISTING BORED PILES
115E
BOTTOM OF MARINE CLAY
EXISTING PILECAP
FILL
Marine Clay
OA
Circle Line Paya Lebar Station – Use of Cross Walls
Use of Cross Walls
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43GeoSS 7 Aug 2012
Use of Cross WallsDTL1 C906
CROSS WALL
Sand
Fill
Kallang
OA
30
40
50
60
70
80
90
100
-5 5 15 25 35 45 55 65
Displacement (mm)
De
pth
(m
)
30
40
50
60
70
80
90
100
-65 -55 -45 -35 -25 -15 -5 5
De
pth
(m
)
IW 894 Design prediction @ IW894
IW 900 Design prediction @ IW 900
87.0 (16m Excavation)
Monitoring at DTL1 C906
44GeoSS 7 Aug 2012
Future Challenges
Top tunnel in Marine Clay
Bottom tunnel in OA
Existing Tunnels
Future Tunnels
Existing Piles /
Barrettes
Transfer Beams and Barrettes for
Underpinning
45GeoSS 7 Aug 2012
Future Challenges
• To match the design of soil improvement methods to be selected based on
� the groutability of the ground encountered
� the targeted engineering property of soil to be
improved
• To have minimum disturbance to surrounding
structures
• To develop new method and technology, e.g.
horizontal grouting techniques
46GeoSS 7 Aug 2012
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2
4
53
Managing Risk of Ground Movement Bored Tunnels
1. Loss into tunnel face
2. Loss between the face and leading edge of shield
3. Tail void
4. Lining deformation
5. Consolidation
47GeoSS 7 Aug 2012
• Phase 1/2 MRT Construction in 1980s: Greathead Shield with hydraulic backhoe excavator or roadheaders / 1 EPBM / 1 TBM
• Compressed air used extensively
• Grouting done through the segments
Greathead Shield EPBM (C301)
Managing Risk of Ground Movement Bored Tunnels
48GeoSS 7 Aug 2012
• NEL: 14 EPBMs (2 Dual Modes), 2 Open Face TBMs
• Automatic tail void grouting
• Face pressure and stability by controlling the extrusion of the spoil through the screw conveyor and the advancement of the machine
EPBM (C705) EPBM (C706) EPBM (C710)
Managing Risk of Ground Movement Bored Tunnels
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49GeoSS 7 Aug 2012
Over Cutting
50GeoSS 7 Aug 2012
Extrados of Extrados of
segmentsegment
Tail void Tail void
groutgrout
Marine clayMarine clay
Automatic Tail Void Grout
51GeoSS 7 Aug 2012
WaterWater EarthEarth
PressurePressure
Increase / Lowering of Increase / Lowering of
Screw Discharge RateScrew Discharge Rate
Increase / Lowering of Shield Advance RateIncrease / Lowering of Shield Advance Rate
Managing Risk of Ground Movement EPBM
52GeoSS 7 Aug 2012
1. Stability Number 2. Stability Number, Nc at collapse
N = (σv + q – σt) / cu
Z
C
D σσσσT
P
Surcharge q
Managing Risk of Ground Movement EPBM
53GeoSS 7 Aug 2012
CIRIA Report 30, March 1996
Managing Risk of Ground Movement EPBM
54GeoSS 7 Aug 2012
Typical Volume Loss for a tunnel of D = 6m by EPB
cu 50 kPa
density 18 kN/m^3
surcharge 10 kPa
depth 20 m
Nc 9
overburden 370 kN/m^2
Face Pressure (%
of overburden) 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Face Pressure 37 74 111 148 185 222 259 296 333 370
N 6.66 5.92 5.18 4.44 3.70 2.96 2.22 1.48 0.74 0.00
1/F 0.74 0.66 0.58 0.49 0.41 0.33 0.25 0.16 0.08 0.00
Volume Loss (%) 6.0 4.0 3.0 2.0 1.3 1.0 0.5 0.2 0.1 0
Managing Risk of Ground Movement EPBM
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55GeoSS 7 Aug 2012
Managing Risk of Ground Movement EPBM
Plastic Nature of Spoils to Maintain
Face Pressure
56GeoSS 7 Aug 2012
No Plug, Material Saturated and Flowing
Managing Risk of Ground Movement EPBM
57GeoSS 7 Aug 2012
Over-excavation in Mixed Tunnel Face
by EPBM
Managing Risk of Ground Movement EPBM
58GeoSS 7 Aug 2012
• Circle Line: 19 EPBM, 8 Slurry TBMs
• Scanners / belt weighing experimented and adopted subsequently
• Slurry TBM used for sections with granite
Slurry TBM (C854) Slurry Treatment Plant EPBM (C823)
Managing Risk of Ground Movement Bored Tunnels
59GeoSS 7 Aug 2012
Face pressure is maintained by
controlling the volume difference of the
bentonite suspension supplied to the chamber and the suspension combined
with excavated material removed from
it
Managing Risk of Ground Movement Slurry TBM
60GeoSS 7 Aug 2012
• DTL1: 3 EPBMs
• DTL2: 10 EPBMs + 9 Slurry TBMs
• DTL3: 19 TBMs
EPBM (C902) Slurry TBM (C915) EPBM (C917)
Managing Risk of Ground Movement Bored Tunnels
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61GeoSS 7 Aug 2012
• Review of Major Underground
Infrastructure Construction and
Singapore Geology
• Managing Ground Risk
• Managing Risk of Ground Movement
• Durability of Bored Tunnels
• Conclusions
Deep Excavation and TunnellingPast Experience and Future Challenges
62GeoSS 7 Aug 2012
Durability
• The durability objective is to achieve a
service life, with appropriate
maintenance, of 120 years
• Design measures need to be taken to
achieve the objective.
63GeoSS 7 Aug 2012
• Concrete with low permeability and low
chloride diffusion
• Protective coating to extrados of segment
• Detailing – adequate cover to re-bars,
including drilling positions / bolt pockets.
• Electrically continuous steel cages as
provision for future cathodic protection, if
required.
Durability Measures
64GeoSS 7 Aug 2012
Typical Durability Problems
65GeoSS 7 Aug 2012
Typical Durability Problems
66GeoSS 7 Aug 2012
• Simple bitumastic sealing strip
• Composite neoprene and bitumastic
strips
• Neoprene gaskets
• “Hydrotite” gaskets
Technology DevelopmentTechnology Development
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67GeoSS 7 Aug 2012
Neoprene Gaskets / Bitumastic Strips
68GeoSS 7 Aug 2012
Waterproofing Bored TunnelsWaterproofing Bored TunnelsNELNEL
� Contract specification required the use of both EPDM gaskets and hydrophilic sealing strips
69GeoSS 7 Aug 2012
Waterproofing Bored TunnelsWaterproofing Bored TunnelsNELNEL
70GeoSS 7 Aug 2012
Gasket details specified on design drawing
Proposed and accepted gasket
Waterproofing Bored TunnelsWaterproofing Bored TunnelsCCLCCL
71GeoSS 7 Aug 2012
Waterproofing Bored TunnelsWaterproofing Bored TunnelsCCLCCL
72GeoSS 7 Aug 2012
Waterproofing Bored TunnelsWaterproofing Bored TunnelsCCLCCL
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73GeoSS 7 Aug 2012
Durable SFRC Segments
•• Elimination of risk of steel bar Elimination of risk of steel bar
corrosion corrosion
•• Elimination of concrete spalling riskElimination of concrete spalling risk
•• More durable segment with min More durable segment with min
maintenance effort.maintenance effort.
74GeoSS 7 Aug 2012
Durable SFRC Segments
75GeoSS 7 Aug 2012
Durable SFRC Segments
•• SFRCSFRC segments for DTL3: 2350m segments for DTL3: 2350m
of bored tunnelof bored tunnel
Upper track in Kallang; Lower track in OA, short
length in Kallang ~650m
Sungei Road Station
Both tracks in Old Alluvium ~1350m
Both tracks in Kallang
~350m
Kalang Bahru Station
Jalan Besar Station
Cross Over at Jln Besar
Tunnel Escape Shaft
Tunnel Escape Shaft
76GeoSS 7 Aug 2012
•• A more responsive earth excavation A more responsive earth excavation
managementmanagement
•• Continued development of new Continued development of new
technology for durabilitytechnology for durability
Challenges for Future ProjectsChallenges for Future Projects
77GeoSS 7 Aug 2012
• Major land transport facilities to be built
in Singapore
• Progresses have been made
• Challenges to the industry
• Looking for new methods and
technologies to address the challenges
Conclusions
78GeoSS 7 Aug 2012
THANK YOU