USA (Next Media) - The world’s largest tunnel boring machine bumped into a mystery object under downtown Seattlelast Friday, bringing the construction of Highway 99 tunnel to a standstill for almost a week.
The stoppage has given rise to all sorts of speculation — ranging from trash abandoned in a landfill to a buried rail car — but one leading theory is that the machine had hit a boulder and the soil around it is too soft to hold it firmly.
The tunnel boring machine was brought in from Japan to dig a four-lane tunnel to replace the now-defunct Alaskan Way Viaduct. The five-storey-high machine was placed about 60 feet below ground, and has already dug 1,000 feet of tunnel since July.
Two cranes were set up at the spot, ready to tackle the object from above ground. It will take about two weeks for identify the object and formulate a strategy to remove it.
The delay will raise the construction cost of the tunnel, but it is not known how much it would cost.
The US$4 billion project is scheduled to be completed by the end of 2015.