Last March, the tunnel contractor Seattle Tunnel Partners introduced an “aggressive” schedule for repairing the tunnel-boring machine Bertha. Now it appears STP was probably a bit too optimistic in setting a goal of tunneling again by August.
Highway 99 tunnel administrator Todd Trepanier also said that the draining of an aquifer of the waterfront, a step taken to ease the tunnel drilling, was likely to blame for viaduct settlement last November.
In a briefing to the Seattle City Council, Trepanier said the damages to Bertha’s seals and main bearing are more extensive than they expected. After crews took longer than expected to disassemble Bertha’s damaged face, Trepanier said they found the seals behind the cutterhead, which prevent excessive metal-on-metal friction, had been completely worn away, rather than simply damaged. Further, the main bearing responsible for rotating the head had been chipped.
Although the plan has always been to fully replace both, STP has nevertheless walked back their original schedule. According to Trepanier, the contractor will reveal a new plan in June.
Crews have not yet determined what caused the damage, which deeply concerned the council members. “It seems like we should understand what went wrong so it doesn’t happen again,” said Councilmember Mike O’Brien. “The frustration levels are rising,” said the oft-soft-spoken Councilmember Sally Bagshaw.
Their main concern was: If Bertha manufacturer Hitachi-Zosen provided a machine that failed once, what will be different the second time?
Trepanier also confirmed suspicions that settlement of the viaduct last November was a result of crews’ de-watering an aquifer below the city’s surface. He said the aquifer has stabilized and they don’t expect to see any further viaduct settlement.
Settlement in nearby Pioneer Square, said Trepanier, was not the result of tunnel construction, but simply historical settlement in Seattle’s oldest neighborhood. That conclusion potentially puts the responsibility of replacing a damaged water main beneath Pioneer Square on the shoulders of Seattle Public Utilities, not WSDOT.
For now, the tunnel’s completion date is still estimated to be the end of 2017.
