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May 15, 2014 at 5:57 PM

Bertha’s repair pit now under construction

Crews this week began building a repair pit next to stranded tunnel-boring machine Bertha, while the state released new images of how the front end would be lifted out this fall.  A Washington State Department of Transportation pit-cam is webcasting the work.

A WSDOT update this week unveiled some conceptual strategies that are either new, or have been tweaked since earlier visualizations.

  • A huge wall of grout will be poured behind the machine’s cutting face, to block groundwater from following Bertha into the repair pit.
  • Groundwater will be pumped away before Bertha begins a 45-foot journey forward, toward the repair zone.
  • Dirt won’t be scooped from the pit until after Bertha arrives through the south end, penetrating a ring of new, 120-foot-deep concrete pillars.
  • The rotary cutters, a ring-shaped drive axle and the main bearing will be hoisted together to the surface, by a gantry crane that sits on top of previously-sunk concrete pillars — a lift of some 2,000 tons. Then the parts would be disassembled, so a new bearing and seals can be installed.

After the tunnel drill penetrates the deep, ring-shaped pit in September, dirt would be removed. A red gantry crane would lift the cutter (green) and bearing (black) to the surface for repairs. (Image by WSDOT)

“It’s at that point that the contractor is going to be able to fully assess the damage to the seal array,”  said Matt Preedy, WSDOT’s deputy Highway 99 administrator, at a legislative hearing Wednesday, echoing previous remarks by Seattle Tunnel Partners (STP) project director Chris Dixon.  Until they can reach the bearing, STP and machine builder Hitachi Zosen won’t fully understand the causes of seal failure and overheating Dec. 6, though STP has blamed a buried steel pipe for damaging several cutting teeth.

STP has set a goal to resume drilling by March 2015. STP has said it can open the four-lane tunnel to traffic by November 2016, but WSDOT Secretary Lynn Peterson has said she’s skeptical about being ready by then.

Hitachi Zosen has yet to issue a detailed repair plan, which the state says is to be published June 16. The reassembly will include additional monitoring devices inside Bertha, said Preedy.

“The contractor is extremely motivated to make sure this machine is fixed and that it’s fixed right,” he said.

As for costs, Preedy said the project has $170 million in contingency funds remaining. The state has denied $157 million of the $188 million in claims by STP to date, and is still examining the other $31 million.  Linea Laird, WSDOT’s chief engineer, said the odds are extremely low that the state will lose in cost disputes. She reminded lawmakers that STP obtained insurance policies and a $500 million performance bond, designed to help assure completion of the tunnel, even if contractors can’t or don’t finish.

Meanwhile, the state has already made well over $1 billion in progress payments to STP, and some 400 workers are employed as construction continues at the north and south portals.

Rep. Gael Tarleton, D-Seattle, aired her worries that Metro bus reductions and worsened traffic congestion are coming soon to Highway 99 commuters. She urged WSDOT to broaden its public communications to deal with issues beyond the drilling machine.


Comments | Topics: bertha, Highway 99 tunnel, Seattle Tunnel Partners


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