Planning, Design and Construction of Underground Infrastructure in Singapore

Ow Chun Nam Director, Land Transport Authority

• Underground Infrastructure in Singapore

• Challenges • Site Investigation

• Deep Excavation

• Bored Tunnelling

• Conclusions

Planning, Design and Construction of Underground Infrastructure

Rail Network Expansion by 2030

RTS Link Between Singapore and Johor

• Singapore to Kuala Lumpur

• 315km, 90mins travelling time

• Operational in 2020

• Possibly part underground

High Speed Rail Link

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

Transmission Cable Tunnel Route Overview

MARYMOUNT

THOMSON PIE

GAMBAS

SEMBAWANG

MANDAI

NS Tunnel

EW Tunnel

AYER RAJAH

NORTH

BUONA VISTA

HOLLAND

DUNEARN

RANGOON

MAY ROAD

INTERFACE

KALLANG

AIRPORT ROAD

TAGORE

ANG MO KIO

PAYA LEBAR

JIP Tunnel

BENOI

PIONEER

PESEK

WEST JURONG

ISLAND

• Underground Infrastructure in Singapore

• Challenges • Site Investigation

• Deep Excavation

• Bored Tunnelling

• Conclusions

Planning, Design and Construction of Underground Infrastructure

• 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

• Continuous process for entire duration of project

Objectives of Site Investigation

• Boreholes too widely spaced

• To have more boreholes – practical problems

Challenges – Boreholes Spacing

Challenges – MRT Tunnel

Tunnel Alignment

41m

65m

56m 58m

Potential JTC 2nd Link Immersed Tunnel

PUB – NIPE Tunnel DTSS Phase 2 (Future) Upper/Lower Limits

1.6km 3.2km 0.4km

PROPOSED JURONG ISLAND – PIONEER TRANSMISSION CABLE TUNNEL

Challenges – Tunnelling under Water Bodies

BH-169 (GL-49m)

ABH-216 (GL-49m)

ABH-214 (GL-36m)

Tender stage : 4 Boreholes

▼Approximate Level of Rock Head

Ground LevelRL 102.7m BH-214

FILL

N=0

M

N=0

F2

N=1~12

F1

N=7~19

G-V

N=41~86

G-I, II

N=76~100

G-III

R=20~80%

G-I,II

R=90~100%

E

N=9

G-III

N=54~67

ABH-215 (GL-66m)

• Tender Design

• Rock head level = 70.5m as per GIBR

• Diaphragm wall depth = 32m

• Shotcrete & rockbolt for lower shaft (in G-III/G-II)

Challenges – Variable Rockhead

Deep shaft ~60m depth

• Tender Stage Borehole = 4 nos

• 1st Stage Add Borehole = 5 nos

• 2nd Stage Add borehole = 10 nos

ABH-D-01 (GL-57m)

ABH-D-05 (GL-42m)

BH-169 (GL-49m)

ABH-216 (GL-49m)

ABH-D-08 (GL-31m)

ABH-D-06 (GL-42m)

ABH-215 (GL-66m)

ABH-D-04 (GL-67m)

ABH-D-07 (GL-62m)

ABH-D-02 (GL-43m)

ABH-D-03 (GL-69m)

Option-2 7m move

ABH-D-09 (GL-57m)

ABH-D-10 (GL-62m)

ABH-D-11 (GL-49.5m)

ABH-214 (GL-36m)

ABH-D-12 (No Rock head)

ABH-D-13 (GL-45m)

ABH-D-14 (GL-65m)

ABH-D-15 (GL-54m)

• From additional SI

• Rock head level (G-III) is much

deeper than original

• Max difference in rock head

level (G-III) is 25m

• Alternative construction

method is needed due to new

geological information

Challenges – Variable Rockhead

Challenges – Variable Rockhead

Option 1 – To relocate shaft

7m

Challenges – Variable Rockhead

Option 2 – Original location with redesigned shaft

GIBR Rockhead Level

Commonly used methods • Electrical resistivity

• Seismic refraction

• Seismic reflection

• Surface wave method

• Geo-tomography

Geophysical Survey

More efficient and accurate methods are required

to determine

• rock levels

• depth of piles

to minimise risk of underground construction in

urban areas

Challenges

• Underground Infrastructure in Singapore

• Challenges

• Site Investigation

• Deep Excavation

• Bored Tunnelling

• Conclusions

Planning, Design and Construction of Underground Infrastructure

Challenges

Deep Excavations in Soft Clay without Ground Treatment

Deep Excavations in Soft Clay with Ground Treatment

Ground Treatment

Typical Station Excavation Depth

Deep Excavation – Bras Basah Station

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

Deep Excavation – Bras Basah Station

Deep Excavation – Bencoolen Station

Subway

NAFA Campus 1 NAFA Campus 2

Bayview Hotel

Plaza By The Park

SMU

NAFA Campus 1

Slide 26

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Strand Hotel

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Hotel 81

Ho

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Somerset Bencoolen

Manulife Centre

Bayview Hotel

NAFA Campus 2

New Dev’t. NAFA Campus 1

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Subway link to SMU

Project Challenges

1. Built-up corridor

-- close proximity to existing buildings

-- very deep station box (43m below ground)

-- thick layer of hard ground (boulders)

-- restricted working hours due to stakeholders requests

2. Pedestrian walkway & vehicular access to buildings to be maintained at all times

Space Furniture

C936 Bencoolen Station SM

U

Bayview Hotel

NAFA Campus 2

New Dev’t.

Station Footprint

Station Excavation – DTL3

CROSS SECTION

BENCOOLEN STREET

43.

2m

Need for Horizontal Grouting

Top tunnel in Marine Clay Bottom tunnel in OA

Existing Tunnels

Future Tunnels

Existing Piles / Barrettes

Transfer Beams and Barrettes for Underpinning

Cable Tunnel – Deep Shafts Utility building (above ground)

Shaft (~60m)

Adit

Tunnel enlargement

Cable tunnel

Soil/Rock Interface

Deep Shaft – Rock Fissure Grouting

• Underground Infrastructure in Singapore

• Challenges • Site Investigation

• Deep Excavation

• Bored Tunnelling

• Conclusions

Planning, Design and Construction of Underground Infrastructure

• 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

Construction Methods

Greathead Shield EPBM (C301)

• NEL: 14 EPBMs (2 Dual Modes), 2 Open Face TBMs

• Face pressure and stability by controlling the extrusion of the spoil through the screw conveyor and the advancement of the machine

• Automatic tail void grouting

Construction Methods

EPBM (C705) EPBM (C706) EPBM (C710)

• Circle Line: 19 EPBM, 8 Slurry TBMs

• Scanners / belt weighing experimented and adopted subsequently

• Slurry TBM used for sections with granite

Construction Methods

Slurry TBM (C854) Slurry Treatment Plant EPBM (C823)

• DTL1: 3 EPBMs

• DTL2: 10 EPBMs + 9 Slurry TBMs

• DTL3: 19 TBMs

Construction Methods

EPBM (C902) Slurry TBM (C915) EPBM (C917)

• Expansion of underground rail system constrained by tight time schedule

• Significant number of TBMs required over a short period of time

• TBM manufacturing and delivering lead time critical

• Client procurement an effective way to manage this

• Possible cost savings from direct procurement from the TBM manufacturers

• Procurement of TBMs restricted to areas with homogeneous soil such as Old Alluvium

• Bulk procured 10 nos Downtown Line Stage 3 TBMs – Novated to successful civil contractors

TBM Bulk Procurement

10m

20m

30m

40m

50m

60m

70m

Deep Tunnels

Underpasses & Shopping Malls

MRT System

Cable Tunnel

Common Services Tunnel

Deep Tunnel Sewerage System

Underground Expressways

Sewers & Gas Pipes

Source : The Straits Times, 11 Feb 12

• Specifications beefed up

• 19 inch disc cutters introduced

• 2 x double compartment manlock required

• Probe drills permanently mounted

• Front midget drill provided

TBM Specifications

Permanently Mounted Drills

Page 39

TBM Front Drilling

Tunnelling through Tight Curves

75m radius curve

Tunnelling through Tight Curves

• Major underground facilities to be built in Singapore

• Challenges to the industry

• New methods and technologies to address the challenges

Conclusions

THANK YOU

MRT Network in Singapore by 2020

• To match the design of soil improvement methods to

• 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

Challenges