Singapore high voltage cable tunnels

Large diameter tunnels for high voltage power circuits

Nearly 30km of large diameter tunnels ranging in diameter from 3.5m to 6m have been designed to carry high voltage power cables in Singapore for PowerGrid. Of these, approximately 6km are currently under construction. The 200 million Singapore dollar project began when PowerGrid commissioned Mott MacDonald, in association with Development Resources, to undertake a study into the feasibility of constructing large diameter tunnels to accommodate HV power cables.


Partition walls being errected in Gambas shaft

The initial scope of the study addressed the feasibility and implications of installing high voltage cables in tunnels, plus the design of two tunnels between Senoko power station and Gambas Avenue in the north of Singapore and between the sub-stations at Ayer Rajah in the west and Paya Lebar in the east. The study also developed route options and planning procedures for constructing an island-wide network of cable tunnels.

The Senoko to Gambas Avenue tunnel comprises 1.7km of twin 3.5m diameter tunnels accommodating ten power circuits. This contract includes the construction of four deep shafts. The Ayer Rajah to Paya Lebar tunnel totals 17km in length and measures 6m in diameter, also housing ten power circuits. The design includes ten shafts, with a maximum depth of 55m for general construction purposes plus cable entry and the permanent ventilation of the tunnels.

The feasibility of a third tunnel between Seraya and Labrador Sub-station, along the west coast of the island was also included in the study. The 8.5km route (4km of undersea tunnel and 4.5km of land tunnel) examined new bored and immersed tunnel solutions and the refurbishment of the existing undersea cable tunnel. Preliminary engineering was undertaken and tender documentation prepared to enable design-and-build contracts to be sought.

Fundamental to the design are the cooling requirements for the power circuits, the overall ventilation of the tunnels and space for installation of the circuits, safe working, maintenance and jointing. The tunnels and control buildings are equipped with fire and life safety facilities designed and specified by Mott MacDonald specialists.

Our commission on the project included the management of the overall tender process and went on to involve construction supervision. Completion of the Gambas Avenue and Labrador tunnels is scheduled for 2005.


TBM assembly in Gambas shaft


Gripper shield front


Errection of cutter head in Gambas shaft


Completed east tunnel of Senako Gambas project

source:
http://www.tunnels.mottmac.com/projects/?mode=type&id=3317

New utility tunnel for Africa’s busiest harbour

Durban Harbour is the busiest container port and harbour in Africa, and approximately 5000 ships visit it each year. As part of the approximately £80 million harbour expansion, a new 4.5m diameter, 500m long tunnel to carry services under the harbour, will replace an existing immersed tube tunnel when the harbour is widened and deepened in 2006.


Northerly view across entrance of the harbour, along the line of existing tunnel

Dredging works for the harbour expansion will cut through the existing tunnel. This means that the new, longer and deeper tunnel needs to be in place and fully fitted-out before the harbour expansion can begin – resulting in a tight design and construction schedule.

Mott MacDonald was part of the team that won the design competition for the type of tunnel that should be constructed, and was awarded the contract to develop the tunnel for Durban’s eThekwini Municipality Water and Sanitation. The competition involved both the new utility tunnel and a 'people mover' tunnel, which would ferry people across the harbour to help in promoting tourism. However, this second tunnel was omitted from the construction contract.

Working with South African engineers, Goba, our design role involved providing technical assistance on the various tunneling options as well as advice on the people mover options and soft ground tunneling. South Africa has strong experience and knowledge in hard ground tunneling, but not as much practice in soft ground tunneling. The ground conditions encountered included river deposits and sandy clay which suited the use of a slurry tunneling machine, which had not previously been used in southern Africa.

Construction work on the tunnel commenced in mid 2005. Of particular note was the steep 20%gradients on each side of the crossing, and the use of a purpose-built vehicle to deliver the tunnel segments. Mott MacDonald had a permanent presence on the site during construction. Although the start-up of the tunneling works proved difficult, the works were completed only slightly behind schedule in August 2006.


Exisiting tunnel landfall structure on the southern side of the harbour entrance


Delivery of the Tunnel Boring Machine


Segments are stored ready for use


TBM being lowered into shaft

The TBM is prepared for launch.

Purpose-built vehicle for segment delivery


Test ring of tunnel segments

source:
http://www.tunnels.mottmac.com/projects/?mode=type&id=9568

US Perspective: Challenges of Underground Facilities in Urban Areas

written by:

A.E. Elioff, Senior Professional Associate Project Management, Tunnel Engineering, PB Americas, Inc. and
C. Laughton, Project Manager for Underground Design and
Construction at Fermi National Accelerator Laboratory

The presentation will illustrate challenges to underground construction (in the USA, urban areas) using illustrations from both successful and unsuccessful underground projects – and the impact of these on current and planned underground construction. Projects are expected to include CSO/Water tunnels, NUMI and DUESL Projects,
WAMATA extension, (Virginia) Alaska Way Viaduct - Seattle, Los Angeles Metro System and Central Artery in Boston.

Paper

US Perspective: Challenges of Underground Facilities in Urban Areas

Presentation

US Perspective: Challenges of Underground Facilities in Urban Areas