Update| 5:35 p.m:
The Highway 99 tunnel machine will remain shut down for perhaps another week of inspections and strategizing, after it churned forward at abnormally high temperatures Tuesday and Wednesday.
After a seven-week shutdown, Seattle Tunnel Partners (STP) restarted the drill known as Bertha and bored ahead two feet on Tuesday. The machine ran hot, so STP “made adjustments” and pushed ahead two more feet Wednesday, according to a state Department of Transportation (DOT) update this morning.
Sensors in the mixing chamber, where dirt falls into the machine through the round cutterhead, were showing 140 degrees, which set off a warning light in the control room, said Todd Trepanier, tunnel administrator for DOT. Normal temperature is about two-thirds that high, officials said.
The problem is similar to a temperature spike in early December, prompting operators to turn the machine off. Steel pipe got into some moving parts that week, but an 11-day followup inspection in January spotted no major damage to the machine or obstructions in the soil, DOT said.
Today’s news is a setback because tunnel officials say they haven’t yet pinpointed the problem.
Contractors haven’t noted any damage to the internal motors and bearings of the $80 million machine’s rotary drive shaft, DOT said.
Trepanier emphasized, in a message to lawmakers, that the team is dealing with the world’s largest machine in complex soil conditions.
The excavation has faced nearly four months of various delays, but DOT holds out hope of regaining enough speed to open the four-lane tunnel to traffic by the end of 2015. “It’s important for us to understand in mining there will be incidents that occur,” Trepanier said. He said he remains confident STP will solve the problem.
Trepanier, whose engineering background is in roads and bridges, including Snoqualmie Pass, said he’s not panicked over the uncertainty because DOT can consult numerous tunnel experts. The state is gathering a special troubleshooting panel, led by Colin Lawrence of Hatch Mott MacDonald in New York. Lawrence said in a message that given the sensitive situation, it would be unprofessional for him to discuss the analysis until it’s done.
Bertha has traveled 1,023 feet of a planned 9,270 feet from Sodo to South Lake Union. The four-lane, tolled tunnel will replace the earthquake-prone Alaskan Way Viaduct, built in 1953.