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After spending weeks searching for what might be blocking the Highway 99 tunneling machine, officials say there’s another problem: Bertha is running hot.

Adding to the trouble, project managers say they don’t know why.

High temperatures near the machine’s cutting face prompted contractors to stop mining after the drill advanced a total of 4 feet in test runs Tuesday and Wednesday. And that ended Bertha’s attempt to resume mining after an eight-week layoff.

A warning light was triggered in the control room, Todd Trepanier, tunnel-project administrator for the state Department of Transportation (DOT), said Friday.

Outside experts will confer with the state and tunnel contractors over the next week to figure out what to do next.

This unexplained stoppage is a setback for the world’s widest single-bore tunnel. Since its July 30 start, the machine has mined just 1,023 feet of the 9,270-foot route from Sodo to South Lake Union.

A similar temperature spike occurred in early December, and the rate of dirt removal plummeted. Bertha advanced only 4.4 feet in three hours just before operators shut it down Dec. 6.

It took weeks for Seattle Tunnel Partners (STP) to pump away enough groundwater to safely allow an 11-day inspection of the front end, which found a concrete chunk and some steel pieces from a pipe Bertha struck Dec. 3, but no major obstacles.

With steel pieces out of the way, the continued overheating suggests a deeper challenge than, say, taking a fork out of the kitchen disposal.

“Although their (STP’s) investigations to date have provided a great deal of information, we will not be able to definitively identify the issue or issues facing the machine until tunneling experts complete their review,” DOT announced Friday.

Trepanier said he still has confidence in the STP construction team, led by Dragados of Spain, Tutor-Perini of California and engineering firm HNTB based in Kansas City, Mo., as well as the $80 million Hitachi machine.

“There’s a lot of complexity with the machine, a lot of complexity with the mining,” Trepanier said. “We’ve had a lot of conversations with STP about this, and the first thing that they like to tell us, particularly the side that has experience with tunneling, is this should not be alarming. … When you’re using TBM (tunnel-boring) machines … issues like this occur throughout the drive.”

Bertha restarted Tuesday and drilled a planned 2 feet, as an experiment after the long outage.

The 2 feet is significant because it allowed workers in back to fasten the 149th of the tunnel’s 6½ -foot-wide concrete rings that will form the highway tube. With the ring in place, STP could then spray concrete grout into the 7-inch space between the ring and the soil, and troubleshoot the grout jets and other components. (The 571
3-foot-diameter rotary cutting face is necessarily wider than the tunnel being assembled behind it.)

Temperatures near the cutter reached 140 degrees, at least 1½ times the standard level, DOT managers said.

The contractors made several adjustments, trying to reduce friction and heat, then mined another 2 feet on Wednesday. Temperatures spiked again. The sensors are in the mixing chamber, where soil falls through the spinning face and enters the conveyor system to exit the back of the machine.

STP hasn’t noted any extreme heat or damage in the cutter’s drive-shaft motor or bearings, according to Trepanier. STP has been referring questions this week to the state.

Trepanier said the first 1,500 feet between Sodo and the Alaskan Way Viaduct are a break-in phase, and interruptions are expected.

Colin Lawrence, a New York-based tunneling veteran leading the new DOT technical team, said in a message it would be unprofessional for him to discuss the analysis until it’s done.

The project’s financial risk-review team has also reconvened, but chairwoman Patricia Galloway, of Cle Elum, Kittitas County, declined to comment this week.

The $2 billion tunnel budget currently includes $120 million in contingency funds. Trepanier said Friday he won’t speculate about costs of delays, or how much money STP might seek in claims or lawsuits.

Mike Lindblom: 206-515-5631 or Twitter @mikelindblom