Tunnelling and traffic management are the main focuses of work on the Shatin to Central Link.
The last of the five MTR projects to finish will be the 17km, £5bn Shatin to Central Link, which will run from Shatin, in the northern New Territories, through Hung Hom station in southern Kowloon, across Hong Kong’s Victoria Harbour and into an underground station at Admiralty on Hong Kong Island. This project is being constructed in two phases, with phase one now underway following the award of the first two major civils contracts last year.
“We have to construct a diaphragm wall and still maintain traffic flows. They looked at how to cater for these flows within the construction sequence”
Philco Wong, MTR Shatin to Central Link general manager
Phase one of the government financed project covers the Kowloon and New Territories sections. Phase two, which is due for completion in 2020, covers the immersed tube crossing of Hong Kong’s Victoria Harbour and the Hong Kong Island section which terminates at Admiralty MTR station (see box).
The first phase also incorporates the above ground Ma On Shan Line in the New Territories. This will feed into the new Shatin to Central Link track alignment at Tai Wai in the New Territories. Ma On Shan Line station platforms will be extended to accommodate eight car trains which will replace the existing four car service between Wu Kai Sha and Tai Wai.
Most of the Shatin to Central Link route is in tunnel. South of Tai Wai it passes through Lion Rock mountain and then under densely built up Kowloon (NCE 3 March 2011). Last October, Vinci Construction Grands Projets won the £227M contract to build the 2.25km drill and blast section through Lion Rock mountain, north of Kowloon. Although drill and blast through rock is considered relatively straightforward, this tunnel will pass within 6m of an existing water tunnel, so at this point the tunnel will have to be formed without explosives.
Vinci’s contract also includes construction of the 1.4km twin bored tunnel section through soft ground to the south of the drill and blast section. This will be built using a 7.4m diameter slurry tunnel boring machine.
Further south, a Samsung/Hsin Chong joint venture has a contract covering a mixture of 1.6km of mixed ground bored tunnel and two cut and cover stations at Ma Tau Wai. The cut and cover work for the station under the six lane Ma Tau Wai Road in Kowloon is attracting a great deal of attention at present, largely because of the introduction of an extensive, widely publicised four year temporary traffic management programme.
Excavating the 320m long 30m deep Mau Tau Wai station box is a sensitive operation, as the buildings lining the route are old and there is a risk of excavation induced subsidence
The underground box will be under a busy main road, lined with ageing buildings. So the station is being excavated from the surface along the line of the 22m wide, six lane road, necessitating an extensive programme of traffic management to enable the contractor to open up its excavation. “We have to construct a diaphragm wall and still maintain traffic flows,” says MTR Shatin to Central Link general manager Philco Wong.
The area is densely populated. Twenty seven bus routes use the road and which is a key transport artery for more than 30 local schools, so traffic disruption has to be kept to a minimum.
“We used a traffic consultant to study the traffic and pedestrian flows. They looked at how to cater for this flow within the construction sequence,” says Wong.
The result is a four year programme of traffic diversions and partial road closures while the station box is created using top down construction method.
In December, three lanes were closed to make way for construction. After 12 months the closure will switch to the other side of the road so the other half of the diaphragm wall can be built. The third phase involves occupying traffic lanes in the centre of the road.
Excavation of the 320m long, 30m deep three-level station box is a sensitive operation, as the buildings lining the route are old and there is a risk of excavation induced subsidence. The solution is to cast over 40 temporary cross walls between the two sides of the diaphragm wall to give it extra strength until the station slabs are complete. The cross walls can then be knocked through during top down excavation work.
Further south at Hung Hom, MTR is preparing to award the contract to remodel the station, which is currently the terminus and interchange for the West Rail, East Rail and Intercity lines.
When the project is complete, Hung Hom will have been transformed into a through station. The new line from the north will connect to West Rail, which runs out to the western New Territories. The existing East Rail Line which runs north to the border with mainland China will then be extended across Hong Kong’s Victoria Harbour to stations at Wan Chai North and at Admiralty.
To transform Hung Hom, MTR is abandoning the existing terminus platforms of the East Rail and West RailLines under the western side of the station and moving the track across to the disused freight sidings under eastern side of the station.
Here it will create a double deck interchange under the existing station concourse, excavating the lower level, from the existing ground level, using top down construction.
In addition a row of columns supporting the station concourse will be underpinned to accommodate the excavation work, and the concourse area will be reconfigured so escalator links to the new platforms can be cut through the existing concourse slab.
As most of this work will take place in a disused area under the station, it is hoped that disruption to passenger flows and station operations will be minimal.
“If we do it properly, a lot of people will be unaware that we are doing major civil engineering work there,” says MTR Shatin to Central Link design manager Clement Ngai.
This year the project is expected to move up a gear as remaining civil engineering contracts are awarded. Completion of phase one is scheduled for 2018.
The Shatin to Central Link project is in two phases so that work on the harbour crossing section does not clash with construction of the Central-Wan Chai Bypass within Causeway Bay Typhoon Shelter on the north shore of Hong Kong Island.
The bypass is being constructed in cut and cover tunnel within a temporary land reclamation. It will also incorporate some of the work needed for the immersed tube’s southern approach. Phase two links the immersed tube, Exhibition station and the terminus at Admiralty. The terminus box is being created by contractors working on the South Island Line project, which is due to finish earlier (see p4). The whole Shatin to Central Link is expected to be complete in 2020.