Skanska is continuing to make very slow progress on its tunnel drive between Tsing Yi and Stonecutters Island on Hong Kong’s troubled strategic sewage disposal scheme (SSDS).

The Swedish contractor is averaging about 7m/month and has to stop tunnelling for about ten days after each cut while efforts are made to treat the poor ground.

One industry source told T&T International: “In good rock, Skanska could expect to bore 300m/month. However, the firm is currently doing more than ten times less.” He denied that work had stopped completely, although he confirmed the TBM was halted while the attempts were made to secure the ground after the next advance.

Skanska’s TBM is currently under the Kwai Chung container shipping complex, the world’s busiest container terminal, which traverses the Tolo Harbour fault.

The fault is believed to be about 30m wide and runs diagonally south-west to north-east across the route of the tunnel, part of a 25km sewage collector system.

The insider added: “Skanska is drilling and grouting to advance very slowly and is also using steel ribs and lagging. It has probably a couple of months to go before it enters better ground.”

The company is wary of moving too fast for fear of causing an incident similar to the cave-in that occurred in February 1998, which led to an eight month stoppage while a remedial plan of action was drawn up.

It is understood there has already been some settlement of at least 10mm within one of the terminals at Kwai Chung. The terminal operator, Hongkong International Terminals, has declined to comment. The issue is sensitive because any ground movement could adversely affect the operation of rail-mounted container handling cranes.