3-foot chunk stuck in Seattle tunnel machine
The large object is either a boulder or piece of concrete that got stuck within the massive spokes of the machine called Bertha, said state Department of Transportation spokeswoman Laura Newborn. Crews have also found metal and plastic piping in the machine but have not concluded what exactly has been causing problems for the machine.
“None of these things in and of themselves is enough to slow the machine down,” Newborn said.
Tunneling has been halted since early December, an early setback in a $3.1 billion project to replace the Alaskan Way Viaduct along the downtown Seattle waterfront.
Newborn said hyperbaric investigations are continuing in the machine. The hyperbaric work involves pumping air into the chamber in order to stabilize the ground in front of the tunneling machine, allowing crews to work safely in that area.
Crews temporarily lost air pressure in the chamber in recent days and spent Sunday re-establishing pressure so the inspection work could continue. The results of the inspection will be reviewed by a tunneling operation task force convened by the state.
Bertha is designed to easily handle rocks under 3 feet in size because the machine is large enough to simply consume those chunks. Larger boulders could be crushed by the front of the machine as it moves forward, but workers also have the option of breaking apart problematic rocks.
Meanwhile, officials have previously said the machine ran into an 8-inch diameter metal pipe that had been left in the ground in 2002 after the state transportation department checked groundwater in the area.
Bertha is stopped about 60 feet underground and one-tenth of the way toward completing a 1.7-mile tunnel. It will carry Highway 99 traffic and allow the removal of the Alaskan Way Viaduct.
Follow AP Writer Mike Baker on Twitter: https://twitter.com/MikeBakerAP
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