Deep Excavation and Tunnelling Past Experience and Future Challanges

09/08/2012

Deep Excavation and Tunnelling Past Experience and Future Challenges

• 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 Tunnelling Past Experience and Future Challenges D Wen, BSc, PhD PE, PE(Geo), AC(Geo), CEng, MICE, MIEAust, CPEng

GeoSS 7 Aug 2012

温大志

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GeoSS 7 Aug 2012

Major Underground Road Tunnels

MRT Network in Singapore North

Woodsville Interchange: Total tunnel length: 0.69km; Opened 28 Jan 2012

North-East

North South Expressway Tunnel and Semi Tunnel : 12.3 km to be completed around 2020

NSL East

EWL

Singapore Underground Road System: underground road tunnels

GeoSS 7 Aug 2012

KPE: Total tunnel length: 9km; Opened 26 Oct 2007 and 20 Sep 2008

CTE: North Tunnel: 0.7 km; South Tunnel: 1.7 km; Opened: 21 Sep 1991

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Fort Canning Tunnel: 0.35 km; Opened 16 Jan 2007 MCE Tunnel : 3.5km to be opened at end 2013

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Deep Tunnel Sewerage System

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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Geological Process

Caverns • Rock Caverns in Jurong Formation • Rock Caverns in Bukit Timah Granite Formation

M OA

FCBB

GV

F/E

S4 GIV

GI/GII/GIII Jurong Formation (Sedimentary Rock)

Bukit Timah Granite (Igneous Rock)

In-filled Valleys Deep weathering of granite

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Mandai

Deep Excavation and Tunnelling

Punggol

Past Experience and Future Challenges

Serangoon Dhoby Ghaut

Boon Lay Scale : -2

0 1 2

Newton 4 (Km)

Outram Park

Kallang Formation

Geological Map

Old Alluvium Jurong Formation

Bukit Timah Granite Gombak Norite

• Review of Major Underground Infrastructure Construction and Singapore Geology • Managing Ground Risk • Managing Risk of Ground Movement • Durability of Bored Tunnels • Conclusions

Reclamation 9

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SITE INVESTIGATION PHASES

Site Investigation

• Continuous process for entire duration of project • Phased approach

• 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

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Desk study Preliminary Detailed SI during construction 11

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COST OF SITE INVESTIGATION

DESK STUDY

Cost of Risk and SI Efforts

• Geological archives/maps • Previous site investigations at the area • Historical land use survey • Published case histories

Optimum Effort Combined Cost

Cost of SI

Cost of Risk Increased Effects of Site Investigation

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COST OF SITE INVESTIGATION

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COST OF SITE INVESTIGATION

• USNCTT (1984): 3% of predicted construction cost • USNCTT: 1.5m borehole for every I m of tunnel • Hong Kong – major projects – around 1%

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. GeoSS 7 Aug 2012

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COST OF SITE INVESTIGATION

Source: United States National Committee on Tunnelling Technology. (1984) Geotechnical site investigations for underground projects. National Academy Press. 16

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Site Investigation Report Site Investigation: field and laboratory works

• NEL: Average borehole spacing 36.5m Geotechnical Factual Report (GFR)

• NEL SI Cost to Civil Cost: 0.216%

Geotechnical Interpretative Report (GIR)

• DTL3: Average spacing 17.5m • DTL3 SI Cost to Civil Cost: 0.283%

Interpreted ground conditions for design, e.g. design sections, design parameters

From DTL

Geotechnical Interpretative Baseline Report (GIBR) GeoSS 7 Aug 2012

Contains the factual data from site investigation & laboratory tests

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Nature, form, composition, properties and structure of the ground and groundwater, artificial obstructions 18

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GIBR

Challenges

• To explicitly share the commercial risk with contractors
Set “Baseline” for commercial purpose
Set minimum requirements for design

Tunnel Alignment 19

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Geophysical Survey

Challenges

• Commonly used methods

• To have more boreholes – practical








problems

• To carry out geophysical survey

Electrical resistivity Seismic refraction Seismic reflection Surface wave method Geo-tomography

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Soil / Rock Interface – Accuracy ?

Geophysical Survey • Methods commonly used for soil / rock interface identification • Results are

Interpreted Profile of Surface Wave Velocity


indirect interpretation of ground condition
influenced by many factors, e.g. utilities, traffic noise Interpreted Rock Profile GeoSS 7 Aug 2012

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Detection of Pile Depth – Accuracy?

Soil / Rock Interface – Accuracy ?

ABH2 6 FILL F1

ABH2 1 FILL F1

GV & GVI GV & GVI

GII & GI

ABH1 8 FILL

F2 E F1 F2 F1 GVI & GV GIII, GII & G1

GIII & GII

Estimated Pile Penetration: 21~22m (or) 26~27 m GeoSS 7 Aug 2012

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Detection of Pile Depth – Accuracy?

Challenges • More efficient and accurate methods are required to determine


rock levels




depth of piles

to minimise risk of underground construction in urban areas

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Deep Excavation and Tunnelling

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Managing Risk of Ground Movement

Past Experience and Future Challenges

• Review of Major Underground Infrastructure Construction and Singapore Geology • Managing Ground Risk • Managing Risk of Ground Movement • Durability of Bored Tunnels • Conclusions GeoSS 7 Aug 2012

GeoSS 7 Aug 2012

• 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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Managing Risk of Ground Movement

Managing Risk of Ground Movement

Deep Excavation

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)

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After Hulme, Potter & Shirlaw (1986)

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Managing Risk of Ground Movement

Managing Risk of Ground Movement

Deep Excavation

Deep Excavation

Singapore Art Museum Cathedral of the Good Shepherd

Reflection Pool Bras Basah Rd

B1 Level

Connection SMU

B2 Level B3 Level B4 Level B5 Level

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Managing Risk of Ground Movement

Managing Risk of Ground Movement

Deep Excavation

Challenges in Urban Environment

Deep Excavations in Soft Clay without Ground Treatment

After Goh (2008)

Ground Treatment Deep Excavations in Soft Clay with Ground Treatment

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Jet Grouting System

Effectiveness of Jet Grout in Marine Clay 160 Jet Grouted slab, 800mm wall

Air Grout Air

Air Water Air Grout

Single tube jet grouting system

Wall deflection, mm

140 Grout

120 100 TREND LINE, 1m to 1.2m DIAPHRAGM WALLS, NO JET GROUT

80 60 40 20

Double tube jet grouting system

Triple tube jet grouting system

0 0

10

20

30

40

Depth from ground surface to hard strata, m After Shirlaw, Tan & Waong (2005)

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Hybrid ground treatment

Deep Soil Mixing (DSM) / Deep Cement Mixing (DCM)

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) 39

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Use of Cross Walls

Use of Cross Walls

114E/W

Masjid Wak Tanjong

115E

EWL VIADUCT

EXISTING PIERS TO BE UNDERPINNED

EXISTING PILECAP

FILL

STRUT S2a

Cross Walls

Marine Clay

115E/W SOIL IMPROVEMENT WORKS by Cross Walls (lean concrete wall)

BOTTOM OF MARINE CLAY

OA

DIAPHRAGM WALL

116E/W

Circle Line Paya Lebar Station – Use of Cross Walls GeoSS 7 Aug 2012

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EXISTING BORED PILES

Circle Line Paya Lebar Station – Use of Cross Walls GeoSS 7 Aug 2012

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Use of Cross Walls

Future Challenges

DTL1 C906 -65 100

-55

-45

-35

-25

-15

-5

5

Existing Tunnels

100

Sand Fill

90

90

87.0 (16m Excavation)

80

80

CROSS WALL 70

70

60

60

OA

50

Monitoring at DTL1 C906

-5

Transfer Beams and Barrettes for Underpinning Top tunnel in Marine Clay Future Tunnels Bottom tunnel in OA

Existing Piles / Barrettes

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40

30

Depth (m)

Depth (m)

Kallang

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IW 894

Design prediction @ IW894

IW 900

Design prediction @ IW 900

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25

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Displacement (mm)

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Managing Risk of Ground Movement

Future Challenges

Bored Tunnels 3

• 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 45

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1. 2. 3. 4. 5.

2 Loss into tunnel face Loss between the face and leading edge of shield Tail void Lining deformation Consolidation 46

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Managing Risk of Ground Movement

Managing Risk of Ground Movement

Bored Tunnels

Bored Tunnels

• 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

• 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

Greathead Shield GeoSS 7 Aug 2012

EPBM (C301) 47

EPBM (C705) GeoSS 7 Aug 2012

EPBM (C706)

EPBM (C710)

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Automatic Tail Void Grout

Over Cutting

Marine clay

Extrados of segment Tail void grout

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Managing Risk of Ground Movement

Managing Risk of Ground Movement

EPBM

EPBM 1. Stability Number N = (σv + q – σt) / cu 2. Stability Number, Nc at collapse

Increase / Lowering of Shield Advance Rate Increase / Lowering of

Surcharge q

Screw Discharge Rate

C Z

σT

D

Water

P

Earth

Pressure 51

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Managing Risk of Ground Movement

Managing Risk of Ground Movement

EPBM

EPBM cu

50

kPa

density

18

kN/m^3

surcharge

10

kPa

depth

20

m

Nc overburden

Typical Volume Loss for a tunnel of D = 6m by EPB

9 370

Face Pressure (% of overburden) Face Pressure

kN/m^2

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

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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

CIRIA Report 30, March 1996 GeoSS 7 Aug 2012

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Managing Risk of Ground Movement

Managing Risk of Ground Movement

EPBM

EPBM

Plastic Nature of Spoils to Maintain Face Pressure No Plug, Material Saturated and Flowing 55

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Managing Risk of Ground Movement

Managing Risk of Ground Movement

EPBM

Bored Tunnels • Circle Line: 19 EPBM, 8 Slurry TBMs • Scanners / belt weighing experimented and adopted subsequently • Slurry TBM used for sections with granite

Over-excavation in Mixed Tunnel Face by EPBM Slurry TBM (C854) 57

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Slurry Treatment Plant

EPBM (C823) 58

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Managing Risk of Ground Movement

Managing Risk of Ground Movement

Slurry TBM

Bored Tunnels • DTL1: 3 EPBMs • DTL2: 10 EPBMs + 9 Slurry TBMs • DTL3: 19 TBMs

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 GeoSS 7 Aug 2012

EPBM (C902) 59

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Slurry TBM (C915)

EPBM (C917) 60

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Deep Excavation and Tunnelling

Durability

Past Experience and Future Challenges

• Review of Major Underground Infrastructure Construction and Singapore Geology • Managing Ground Risk • Managing Risk of Ground Movement • Durability of Bored Tunnels • Conclusions

• 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.

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Durability Measures

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Typical Durability Problems

• 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. GeoSS 7 Aug 2012

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Typical Durability Problems

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Technology Development

• Simple bitumastic sealing strip • Composite neoprene and bitumastic • •

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strips Neoprene gaskets “Hydrotite” gaskets

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Neoprene Gaskets / Bitumastic Strips

Waterproofing Bored Tunnels NEL

 Contract specification required the use of both EPDM gaskets and hydrophilic sealing strips

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Waterproofing Bored Tunnels

Waterproofing Bored Tunnels

NEL

CCL

Gasket details specified on design drawing

Proposed and accepted gasket

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Waterproofing Bored Tunnels

Waterproofing Bored Tunnels

CCL

CCL

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Durable SFRC Segments

Durable SFRC Segments

• Elimination of risk of steel bar corrosion • Elimination of concrete spalling risk • More durable segment with min maintenance effort.

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Challenges for Future Projects

Durable SFRC Segments • SFRC segments for DTL3: 2350m of bored tunnel

• A more responsive earth excavation management

Cross Over at Jln Besar Both tracks in Kallang ~350m Tunnel Escape Shaft

Sungei Road Station

Tunnel Escape Shaft

Both tracks in Old Alluvium ~1350m

Jalan Besar Station

• Continued development of new Upper track in Kallang; Lower track in OA, short length in Kallang ~650m

technology for durability

Kalang Bahru Station

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Conclusions • Major land transport facilities to be built in Singapore • Progresses have been made

THANK YOU

• Challenges to the industry • Looking for new methods and technologies to address the challenges

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