Contractor assessment is underway to prequalify to bid for metro tunnel construction on the West Island Line (WIL), between Sheung Wan (SHW) and Sai Ying Pun (SYP), in Hong Kong.

Submissions were due at the beginning of the month from firms seeking to prequalify to tender under a two-stage process for Contact 703, which is to be awarded on a Target Cost basis.

Bid documents are to be issued next month for submission in November, after which the second stage of the tender process will run over January-August 2009. The contract period is September 2009 to 2013-14.

The programme calls for the Eastbound and Westbound tunnels – approx. 770m and 490m long, respectively – to be driven concurrently. Ground conditions along the Eastbound drive comprise 410m of soft ground, 120 of mixed and 240m in hard rock.

Major ground treatment will be required for the works, both from the road surface and ahead of the excavation face. In addition, some prior backfilling would be needed where the alignment encroaches the existing overrun tunnel lining

for 130m in soft ground. The client, MTR Corporation (MTRC) said building piles are also anticipated along the route of the new tunnels and will need to be removed from within the excavations.

MTRC says the major works will be approximately 6.4m diameter and done by closed face TBM and/or open faced “Greathead” shield with compressed air. The maximum operating pressure would be 3.5Bar, it added. There would also be a section – approximately – 365m long in

good rock cover between the launch shaft and SYP station. Both tunnels will be bored from the launch/entrance shaft in the existing Sai Woo Lane Playground Area, excavated to a depth of 42m including 15m in rock.