Sinkholes seem to be a recurring source of frustration for the state and its contractor, the Seattle Times reports.
Sinkholes seem to be a "recurring source of frustration" for the state and its contractor, the Seattle Times reports. Washington State Department of Transportation

The Seattle Times's Mike Lindblom has a story out today about a history of e-mails and documents showing state officials and tunnel engineers biting their fingernails about the downtown tunnel boring machine.

Earlier this year, Governor Jay Inslee temporarily shut down drilling and put the tunnel's contractors on notice after a sinkhole opened up 100 feet away from Bertha's cutterhead. Seattle Tunnel Partners worked on new conditions dictated by the state before the machine reached a maintenance stop called "Safe Haven 3" in mid-March.

Safe Haven 3 is the last maintenance stop before Bertha drills under the aging Alaskan Way Viaduct itself.

A series of e-mails dug up by public records request, however, show that one geotechnical expert working for the state predicted the problems that would cause the state to temporarily shut down drilling in January. The expert, a man named Gregg Korbin, further predicted that more sinkholes would open up if the project wasn't suspended and the problem sorted out.

Lindblom writes that the upset over the January sinkhole has "heightened the vigilance—you could even say paranoia" among officials and engineers before the machine goes under the viaduct. Further, he writes, sinkholes seem to be a recurring problem:

Documents show that a recurring source of frustration, for both the independent and WSDOT engineers, involves whether contractors are able to keep the dirt firm enough to prevent sinkholes. Tunnelers are supposed to keep a firm plug of dirt inside the conveyor screw, behind the cutterhead, that would assure a consistent pace of soil movement and pressure. STP has sometimes closed gates within the conveyor system to help keep the cutter area filled with dirt, as a balance against more dirt rapidly flowing in.

On March 10, I asked Mayor Ed Murray if he had any concerns about the fact that STP had been drilling on a conditional basis right before the machine was set to dive underneath the viaduct. Murray gave me a non-answer. He said consultants hired by the city were "constantly sharing that information with the state; the state shares information with us when we have concerns."

So did the state share its concerns about sinkholes with the city? I've asked the Mayor's office and will update when I hear back.