A call has been issued for contractors to prequalify for two sewer tunnel contracts with a combined length of almost 20km as part of the second stage of Hong Kong’s Harbour Area Treatment Scheme.

The deadline for submissions to Hong Kong’s Drainage Services Dept is 27 June.

Bidders must have experience of major tunnelling with pre-grouting as the main method to control groundwater at pressures of at least 7 bar. The tunnels will be driven through granitic and volcanic rocks with excavated spans of 4m-5.5m.

The client intends to invite prequalified contractors to bid for the contracts in September. Construction is scheduled to start early 2009 for completion by mid-2013.

In Contract DC/2007/23 the client plans to have approximately 12km of sewer of up at depths of 140m-160m below sea level. The sewer will be built with eight shafts of various diameters.

The second contract – DC/2007/24 – will have a shorter, shallower tunnel and of smaller diameter. The Drainage Services Dept plans a sewer of approximately 7.5km long at depths of 70m-120m below sea level. Seven shafts are to be built for this section of sewer.