Bertha’s nemesis: 119-foot steel pipe
Highway 99 contractors revealed Friday what’s been blocking Bertha, the giant tunnel machine: The obstruction is steel pipe, left buried by a state groundwater study in 2002.
Seattle Times transportation reporter
State officials revealed Friday that the mystery object blocking tunnel machine Bertha is a long steel pipe, left buried in 2002 by one of the Highway 99 project’s own research crews.
The tunnel drill has been stranded for a month near Pioneer Square, with no clear strategy yet to extract the pipe.
The Department of Transportation (DOT) could not estimate how much time and money it will take to get the world’s largest drill moving again.
Bertha’s cutting teeth struck the pipe Dec. 3, yet the DOT and its contractors avoided mentioning the steel as a possible culprit for four weeks, despite an incident in which the machine knocked a 55-foot pipe fragment to the surface.
What the ongoing delay means for taxpayers is unclear, but it’s certainly not good.
The costs will be determined later through negotiations between the state and Seattle Tunnel Partners (STP), maybe even a legal dispute.
The $2 billion tunnel budget includes a $40 million risk allowance for repairs and inspections near the front of the rotary cutting face — plus a $105 million general contingency fund to deal with crises. Matt Preedy, deputy Highway 99 administrator for the state Department of Transportation, said some of that money will be consumed.
The culprit is an 8-inch diameter, 119-foot-long well casing, used to measure groundwater for the Alaskan Way Viaduct replacement project, officials said. Back then, a shallow cut-and-cover tunnel was a leading option.
A jagged piece of the pipe appeared Thursday night, after enough groundwater was pumped out of the machine and soil to allow STP crews a view through the cutting face.
The 2002 well site was listed in reference materials provided to construction bidders, as part of the contract specifications.
“I don’t want people to say WSDOT didn’t know where its own pipe was, because it did,” said state spokesman Lars Erickson.
However, Chris Dixon, STP’s project director, said the builders presumed it had been removed.
“If we had known the pipe was there, we would have removed it,” he said.
Dixon mentioned that Ecology Department rules require well casings to be removed after use. Ecology spokesman Dan Partridge said his department didn’t perform the viaduct studies, and as a general rule, “you do not necessarily have to remove a casing when you remove a well.”
Bertha first encountered the pipe Dec. 3, Dixon said. The clockwise cutting motion pushed part of it above the surface, and fragments showed up in a conveyor system within the machine, he said.
“We saw a pipe come up, out of the ground 6 or 7 feet,” he said. “We continued mining, successfully.”
Workers removed a 55-foot-long piece, he said. For two days, the drill moved along fine, creating what Dixon called “a false sense of security.”
The blockage, which Bertha hit 60 feet below surface, is beneath the area where Seattle settlers dumped fill soil and debris, based on local histories. No metal should be there.
So why didn’t that bizarre pipe hit scare Dixon into halting immediately Dec. 3? He replied Friday the team didn’t realize the pipe extended so deep, and thought workers had removed it all.
On Dec. 6, the cutter turned without grabbing soil. So the operators quit running it the next morning, to avoid harming the $80 million machine.
A modern tunnel machine can chew through dirt, rocks and concrete, but not steel, which can become tangled in the cutting head, or caught in a conveyor screw. Dixon said Friday that “we don’t know” yet whether any moving parts are jammed.
However, the team has found unusual wear on block-shaped cutting tools, and STP is replacing those with new tools on the cutting head.
For the last four weeks, DOT didn’t mention steel pipe as a suspect, and even talked about the cutting-tool swap on Monday as routine. In a Dec. 20 blog post, removed Friday, the DOT said, “We simply don’t know yet” the cause.
Asked about this, Preedy said Friday that initially, the team gave DOT and outside tunnel experts information about the pipe strike.
“In that same two days, there were pieces of boulder that had come out on the [conveyor] belt,” he said. The experts thought the chance of further problems with pipe were low, he said. “At that point in time, we were pretty well convinced it was something else,” Preedy said. For instance, a giant rock deposited by glaciers.
The theory changed this week when vertical-test probes hit small objects, then Thursday’s inspection located buried pipe, he said.
Construction of the four-lane tunnel is three months behind its schedule to be open at the end of 2015.
However, the machine in November was advancing as fast as 50 feet a day, prompting Preedy to say it’s possible to regain time after the steel is removed.
This incident follows other woes at DOT, including an expensive crack repair and delay for Highway 520 bridge pontoons; staff shortages that canceled late-summer ferry runs; and the loss of $175 million in planning costs for the Interstate 5 Columbia River Crossing, before work was halted by a legislative impasse.
On the positive side, work is proceeding smoothly on rebuilding Interstate 90 east of Snoqualmie Pass, and the DOT quickly replaced a downed Skagit River Bridge span.
Quite a bit of work remains to clear the pipe away from Bertha.
Thursday’s inspection included only the top 15 feet of the machine because the rest is flooded with mud and groundwater. STP must somehow check the lower 42 feet of the 57-foot diameter face, perhaps with tunnel-trained divers.
Then the steel must be extracted from above, going through unstable soil, or from within the cutter face.
Dixon said contractors are trying to figure out what methods are possible, while protecting worker safety.
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org.