By Steve Wilhelm, February 24, 2016
After more than a month of state-ordered stasis, Seattle’s tunnel boring machine is moving forward again.
The Washington State Department of Transportation on Tuesday allowed Seattle Tunnel Partners to start moving the Bertha tunnel-boring machine forward another 160 feet, while the state closely monitors the project.
Under new rules, the state is requiring STP to increase its quality controls. The contractor must have people monitoring key positions in the tunnel boring machine and provide daily updates.
Daily meetings reviewing progress are to include representatives from the department of transportation and the contractor.
After a series of fits and starts for the boring machine – which was initially scheduled to be done digging the Highway 99 tunnel to replace the Alaskan Way Viaduct last year – Gov. Jay Inslee ordered tunneling halted Jan. 14 after a sinkhole appeared near where the machine was burrowing.
While STP quickly filled in the hole, state authorities were concerned enough to order the contractor to stop the machine before it starts tunneling under the Alaskan Way Viaduct, and then downtown Seattle.
The machine had started tunneling again Jan. 7, after being stuck for more than two years underground just west of Pioneer Square. STP had to rebuild the front end of the machine with new bearings and bearing seals after the previous parts were damaged before drilling could proceed.
If boring proceeds satisfactorily, STP will be allowed to continue boring another 100 feet to a planned maintenance stop.
There crews will perform final maintenance before the machine bores under the viaduct.
The intent of the 1.7-mile tunnel, at 58 feet in diameter the largest in the world, is to create a highway under Seattle to replace the elevated viaduct. When completed, the tunnel will provide room for two lanes north and two lanes south.
The aging viaduct is considered seismically vulnerable, and the state chose the tunnel option as a way to replace it without unduly disrupting viaduct traffic during construction, and to connect Seattle’s waterfront to downtown.