Singapore awards 35km cable tunnels Sep 2012
Peter Kenyon, TunnelTalk
Contracts totalling US$1.25 billion are awarded for delivery of 35km of deep-level high voltage power transmission cable tunnels in Singapore.
Singapore Power announced Monday (September 17, 2012) six contracts for construction of two intersecting tunnels, 14 utility buildings and associated access shafts and adits, and four temporary TBM launch shafts.
Fig 1. 18.5km north-south alignment and 16.5km east-west alignments

Fig 1. 18.5km north-south alignment and 16.5km east-west alignments

A mixture of up to 10 hard rock TBMs and EPBMs are expected to complete the tunnels in order to keep drive lengths, where possible, to within a single type of geological formation, although mixed ground drives are unavoidable especially along the challenging east-west alignment.
The four companies and JV that will complete the project in six lots are:
• Hyundai Engineering and Construction (South Korea), which confirmed in a press statement a bid price of US$250.2 million.
• Nishimatsu Construction (Japan)/ KTC Civil Engineering and Construction (Singapore) joint venture
• Obayashi Corporation (Japan)
• Samsung C&T Corporation (South Korea) with a bid claimed at US$205.5 million by the International Association of Contractors of Korea (ICAK)
• SK Engineering and Construction (South Korea), for two lots with a bid claimed at US$464.6 million by ICAK.
Table 1. Two cable tunnel alignments split into six lots
NORTH-SOUTH TUNNEL (18.5km)** Award locations
Samsung C&T Gambas
SK Engineering & Construction Mandai*
Ang Mo Kio
Hyundai Engineering & Construction Marymount
May Road
EAST-WEST TUNNEL (16.5km)***
Obayashi Ayer Rajah
North Buona Vista
SK Engineering & Construction Holland*
May Road
KTC/ Nishimatsu Construction JV Kallang
Airport Road*
Paya Lebar
* Temporary TBM launch shaft location
** Design consultant Hatch Mott MacDonald
*** Design consultant WorleyParsons/ AECOM
The tunnels, to be excavated to an i.d. of 6m, run east-west across the island state for 16.5km, and north-south for 18.5km, intersecting at May Road (Fig 1). Design of the north-south section was completed by Mott MacDonald. A JV of AECOM/ WorleyParsons completed design for the east-west section.
In order to avoid private land-ownership related project delays both alignments run for the majority of their length under public roads.
Construction of the four temporary TBM launch shafts at Mandai, Thomson, Holland and Airport Road is to begin early in 2013. The east-west tunnel is scheduled to be completed in May 2017 and the north-south tunnel 11 months later.
"With Singapore's rapid growth and the corresponding increase in power demand we are challenged to sustain the level of reliability in a cost effective way," said Wong Kim Yin, Group Chief Executive Officer of Singapore Power.
Geological investigations carried out as part of the design process, which has been ongoing since the early 2000s, have revealed the alignment crosses a number of geological formations; the Jurong Formation in the west, through Bukit Timah Granite (BTG) in the central zone, a second area of Jurong Formation, the Kallang Formation and then Old Alluvium to the east.
The Jurong Formation has been identified as a variable rock of interbedded sandstones, siltstones and mudstones. The bedrock is expected to be reasonably good for tunnelling, although rapidly varying rock strengths are likely. The most important unit of the Kallang Formation is the Marine Clay, with a maximum thickness of 35m, although 10-15m is more common. The clay is soft to very soft and will require closed face EPBMs.
Mott MacDonald has been actively involved in feasibility studies for deep level TBM bored cable tunnels in Singapore since the early 2000s, and designed the twin running 3.5m i.d. 1.7km-long Senoko-Gambas alignment on the north of the island, which connects Senoko power station to Gambas Avenue. That project, completed in 2005 by a JV of Obayashi (Japan) and McConnell Dowell (Australia), used a Robbins gripper double shield TBM.

6m diameter cable tunnel will be 60m below ground level, under existing infrastucture

The drives had been expected to be through extremely hard granite, but the challenging ground conditions that had been anticipated were even more extreme than expected with high water inflows and flowing ground hindering progress of the first 200m of the first drive. Conditions did improve, and with modifications the JV was able to successfully complete both tunnels in January 2005.
The Senoko-Gambas cable tunnel will connect with the latest north-south tunnel at Gambas, thereby extending the transmission of high voltage electricity from Senoko power station to the south, east and west of the island.

Robbins double shield TBM completed a twin running cable tunnel between Senoko and Gambas, in 2005

Two extremes in one for Singapore's DTSS - TunnelTalk, March 2005
The good, bad and mixed on Singapore's DTSS - TunnelTalk, April 2004
First of six Robbins EPBMs set in Singapore - TunnelTalk, September 2012
Tunnel option for Malaysia-Singapore link - TunnelTalk, May 2012
Singapore DTSS in world's top 100 projects - TunnelTalk, July 2012

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