TUNNELS: Seattle’s S.R. 99 project could be delayed for months

Repairs to tunnel-boring machine may require deep excavation

News Seattle Times February 11, 2014
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The S.R. 99 tunnel project in Seattle could be delayed for months following the latest setback with the boring machine, Big Bertha.


Bertha has been stalled since Jan. 29, and the prime contractor, Seattle Tunnel Partners, is now considering digging a hole up to 115 ft deep in front of the equipment to make the necessary repairs. Once that task is complete the cutting head for the tunnel-boring machine will be removed by crane.


Chris Dixon of Seattle Tunnel Partners said they were looking at four or five options, but the Washington State Department of Transportation released a statement projecting repairs could take months to make. The project is already four months behind schedule.


“What we’re talking about is, they’re going to excavate the shaft, drive 60 or 70 piles, then lift up the cutterhead,” Lee Newgent, executive secretary of the Seattle Building & Construction Trades Council, said. “They’re looking at least six or seven months.”


Whatever the chosen method, deep piles or walls will have to be used to keep the soft soil and groundwater from affecting the work area.


Following a Dec. 7 shutdown it was discovered that Big Bertha suffered damage to its seals which lubricate the $5 million main bearing. Officials believe the main bearing is OK, but will not know for sure until the manufacturer, Hitachi Nosen, visits the site on Feb. 12.

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