Work on the HK$19.5bn (US$2.5bn) second phase of Hong Kong’s deep tunnel sewerage scheme is set to go-ahead after the government announced its commitment to the scheme in mid-June. Design and build bids are expected to be called for the HK$8.2bn (US$1.05bn) tunnelling stage of the project, which could begin construction in 2007-08.

The shift to design and build follows significant construction delays and cost overruns during tunnelling of the first phase, which was awarded on an engineer’s design. Phase one was completed about US$256M over budget and four and a half years late following a raft of problems including high rates of water ingress, cave-ins, machinery breakdowns and the sacking of the original contractors’ joint venture. The switch to a design and build contract was recommended by Maunsell Consultants who had been engaged to carry out an investigation into various procurement strategies.

“Maunsell recommended a DB (design and build) approach as it offers potential time advantage and provides a clearer contractual interface among the employer, engineer and contractor,” the Drainage Services Department (DSD) said. In a briefing paper to local lawmakers at the end of June, the DSD added, “we will start site investigations and environmental impact assessment in 2005 to enable the major construction works to commence in 2007/08. The more challenging tunnelling works are expected to be completed by 2013/14.”

The tunnel works form part of phase 2A of the overall project, which also includes the construction of underground sewage treatment facilities. The plan envisages the construction of a deep tunnel network on Hong Kong and Lamma islands to link up with the existing system.

The deep tunnel network will be built on the northern and western sides of Hong Kong Island. There will also be a section to Lamma Island and another that will link up with the system at Stonecutters Island.

An exact tunnel alignment has still to be fixed, but the total length of tunnel is likely to be about 20km. The plans were announced by Dr Sarah Liao, Secretary for Environment, Transport and Works, following the completion of conceptual and preliminary designs by Camp Dresser McKee International.

The favoured scheme is similar to one of four options revealed by an independent review panel in November 2000 that was headed by Professor Donald Harleman. Harleman was called in to probe the disastrous first phase tunnelling works and recommend a way forward for future phases of the scheme.

Related Files
Map showing the completed Stage 1 tunnels and the planned tunnel alignment for Stage 2