Contractors working on West Rail's northern section have overcome some of the project's toughest challenges over the last 12 months.
Flash floods and very difficult ground conditions had threatened to undermine progress on four of the six stations on West Rail's north section last year. But despite some disruption, work is on schedule with construction of stations at Tuen Mun, Siu Hong, Yuen Long and Long Ping substantially complete.
Tuen Mun and Siu Hong stations are built on piles bored into the bed of a 70m wide nullah or storm water channel. As such, their construction sites were vulnerable to flash flooding during the April to September wet season, while temporary works in the nullah would have reduced flood relief capacity. As a result, the HKACE joint venture compressed piling and column construction at Siu Hong and Tuen Mun into six month segments.
'The main issue for the contractor was to organise the work to maximise the amount of dry season work while utilising the workforce in the wet season, ' says West Rail northern section project manager Gregory Yuen.
As the station structures emerged from the nullah, the contractor reduced the need to use space in the nullah by cantilevering falsework off the station structures, rather than founding it on the flood channel floor.
'The other major challenge was the piling works at Yuen Long and Long Ping, ' says Yuen. Areas of cavitied marble on these sites had caused delays of up to six months because contractor Amec-Hong Kong Construction joint venture had to sink some of its piles to depths of between 120m and 130m before they could find deep enough layers of continuously competent rock.