Tunnel-drilling Bertha to start moving again this week


Tunnel-machine Bertha is supposed to get moving again this week.

After a nearly eight-week stoppage, Seattle Tunnel Partners (STP) intends to resume digging — for two feet — later this week, then give the tunnel-boring machine a checkup, the state announced Monday night.

Another two feet of progress would allow workers to fasten the next 6-foot-wide concrete ring of the new Highway 99 tube, at the rear of the machine. The machine moves forward by pushing off each ring, using 56 hydraulic thrusters.

Basically, there weren’t any major obstacles found in the soil, or inside the huge rotating cutter, during 10 days of inspections, said Matt Preedy, deputy project administrator for the state Department of Transportation (DOT).

Previously, DOT questioned how its contractors were running the giant drill, and demanded answers as to why Bertha operated at high temperature in early December.

STP chose to stop Dec. 6, after 1,019 feet of drilling, when the cutter stopped grabbing soil. Officials were concerned about damaging the machine.

But Preedy said recent inspections haven’t turned up mechanical trouble either.

“The cutterhead turns fine. It’s got torque and got thrust. As far as the contractor can tell, it’s fine,” he said Monday night.

STP director Chris Dixon did not reply to messages seeking an interview. Previously he has blamed a steel pipe, left over from a DOT groundwater test, for damaging cutter parts.

A week ago, the inspections turned up some bent pipe, a 3-foot-wide concrete chunk and plastic fragments, but not much else. Inspections should be finished Tuesday morning, DOT spokeswoman Laura Newborn said.

An expert panel is reviewing data related to the machine’s performance, and Monday night Preedy wouldn’t theorize about what caused the stoppage. “It was probably a combination of things,” he said.

With each week lost, the odds increase that the project will churn through the remaining $120 million or so in contingency funds for the tunnel project. The possibility of lawsuits has made some officials leery about offering details.

Preedy didn’t have an estimate on costs Monday night.

“We haven’t really talked to them (STP). I can’t really speculate on what those will be,” he said.

The state has already paid STP $774 million of its $1.44 billion contract to build the tunnel, ramps at both ends and road decks from Sodo to South Lake Union.

Earlier Monday, a barge was moored alongside Terminal 46 to accept and remove excavated soil from the machine’s conveyor system.

The original schedule called for Bertha to have just passed the Alaskan Way Viaduct by now, to enter the denser and more predictable soils deep below downtown.

Instead, the machine has 500 feet left to go along the waterfront, before it will pause in a “safe haven” of concrete for maintenance, just before diving under the old highway. The team has lost three months because of a glitch during tests in Japan, a labor dispute over who will load the barges and the recent shutdown.

Todd Trepanier, the DOT’s Highway 99 administrator, told The Seattle Times previously that the machine might need to be modified.

The soil where Bertha now sits is saturated by groundwater — about 35 percent water content — from rainfall, runoff and Elliott Bay tides. But Preedy said he didn’t think soaked or soft soil would prevent forward progress.

After advancing two feet, certain parts need a checkup, said Preedy — for instance, a system that sprays concrete grout around the machine and rings, to fill small gaps in the soil, may have become clogged after weeks idle, he said.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com. On Twitter @mikelindblom

 

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