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Yuen Long section

Consultants on West Rail face complex design challenges all along the route.

Detailed design

Ove Arup & Partners Hong Kong

Contract DD-200, 8.8km, including three stations

Design contract value HK$262.75M (£21M)

Noise isn't the only challenge within Ove Arup & Partners' section of the detailed design (see page IX).

Huge underground caverns make the work more complex still. Known as the marble area, it has limestone caverns up to 20m across: 'Big enough for double decker buses - or even a railway concourse,' says construction engineering manager Chris Calton.

Caverns can occur anywhere from 10m underground to 150m down, when solid rock appears. 'We can't go through or across the caverns,' says KCRC northern section project manager Gregory Yuen.

Arup director Naeem Hussain says they have one of the most comprehensive site investigations ever undertaken, based on a 3m grid.

'Every single pile has to be pre-drilled and checked,' Hussain says. 'We are now looking at a development of the design where instead of using large diameter piles we may go for large diameter in combination with micropiles in the cavernous area.'

Calton says this would be a departure from the normal practice in the Building Department in Hong Kong. 'Piles built in accordance with the Ordinance in Hong Kong would generally be end-bearing, but it may save costs to include an allowance for friction too.'

KCRC has invested in a heavy pile load test contract to do advance testing. The large diameter piles are being subjected to both vertical and horizontal load tests.

Supervised by Arup, three field contracts are being carried out by Gammon Construction, Express Builders Company and Bachy Soletanche.

'The results are looking positive,' says Calton. 'That should allow us to make significant savings, both in capital construction costs and in programme.'

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