deep excavation and tunnelling past experience and future challanges

09/08/2012

1

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



Singapore Geology




• Conclusions


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.


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.


17GeoSS 7 Aug 2012


• 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



Singapore Geology




• Conclusions


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)


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


34GeoSS 7 Aug 2012


35GeoSS 7 Aug 2012


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

1

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)


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)


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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


53GeoSS 7 Aug 2012

CIRIA Report 30, March 1996


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


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55GeoSS 7 Aug 2012


Plastic Nature of Spoils to Maintain

Face Pressure

56GeoSS 7 Aug 2012

No Plug, Material Saturated and Flowing


57GeoSS 7 Aug 2012

Over-excavation in Mixed Tunnel Face

by 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)


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)


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61GeoSS 7 Aug 2012



Singapore Geology




• Conclusions


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

09/08/2012

12

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


72GeoSS 7 Aug 2012


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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


75GeoSS 7 Aug 2012


•• 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

deep excavation and tunnelling past experience and future challanges

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