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Eastern front

KCRC

East Rail Extension's Ma On Shan Rail line is fast taking shape following the start of civil engineering work in 2001.

People travelling along the KCR's East Rail line from Hung Hom to Lo Wu get their first glimpse of work on Ma On Shan Rail (MOS Rail) as they emerge from Beacon Hill tunnel just to the east. What was once a driving school, a cycle park and an amusement park is now bristling with piling rigs.

Two contracts are in full swing.

Gammon is busy inserting 458 large diameter piles and 1,109 pre-bored H-piles for the 10 track, Ove Arup-designed depot which will house MOS Rail trains. At the same time, Maeda is building Tai Wai station, a Babtie/Halcrow designed terminus where passengers can switch between the new line and the existing East Rail station.

The station contract was awarded in November 2000, one of the first civil construction packages to be let. KCRC East Rail Extensions director KK Lee says this is because it is on the project's critical path, forming the vital link into the East Rail services.

If other stations finish late, it might still be possible to start running services, but Tai Wai forms the vital link into East Rail and without it passenger numbers would dwindle.

Work is complicated by the site's proximity to the live East Rail tracks. Depot construction has so far involved removing part of the East Rail embankment slope and inserting around 1km of propped sheet piles without disturbing the line. And at the station itself, Maeda has constructed two concrete tunnel boxes under the line by pipe jacking method. One provides pedestrian access through the station while the other is an emergency access tunnel for firefighters.

A drive out to Ma On Shan from Tai Wai reveals construction activity along the entire 11.4km route as stations start to take shape and the viaduct which follows most of its length begins its snaking route over roads, junctions, roundabouts and pedestrian footbridges.

Maunsell Consultants Asia's viaduct design is modelled on the original Ove Arup concept for the 13.4km West Rail viaduct, resting on bearings, rather than the WestRail contractor's alternative series of portals, conceived to minimise maintenance.

Although Maeda bid for the MOS Rail viaduct, it lost out to a lower tender from Necso-China State, which bid with the conforming design. Lee is unconcerned about comparisons with the West Rail structure. He believes that although bearings require maintenance, it will be minmal.

One key difference between the two viaducts is in the erection process. On West Rail, much of the viaduct is in open countryside, allowing space for overhead gantries to be used. The MOS Rail viaduct, however, is being constructed in a narrow heavily built up corridor with little space to dismantle and erect the gantries used to create spans, typically comprising 14, 2.5m long precast segments.

As a result, the contractor is using six travelling underslung gantries to assemble and position precast viaduct box beam segments longitudinally, and one overhead travelling gantry to erect tight curvature spans and to cross road junctions with low headroom.

But, in many respects, the two viaducts will be similar. Both will incorporate noise reducing floating track slabs and will use an elevated trackside walkway to capture train noise.

As with West Rail, progress has been encouraging during the civil construction phase. Last year, work on the project was hit by unusually bad weather which hampered the intensive piling operation at the depot. But Gammon has kept to schedule by increasing the number of piling rigs on site. 'We had expected them to have 20 piling rigs at peak. Now they are mobilising over 30, ' says Lee.

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