Governor Jay Inslee has ordered Seattle Tunneling Partners (STP), Highway SR 99 tunnel contractors, to suspend drilling the deep-bore tunnel along the Seattle waterfront, until a sinkhole that formed this week is fully investigated.
According to WSDOT, despite contractors efforts to fill the sinkhole with cement, the ground above the tunnel boring machine named Bertha continues to sink.
Thom Neff, a Boston-area megaproject consultant who warned of tunneling risks in a 2010 report to then-Mayor Mike McGinn, said the area’s wet dirt is difficult to measure, so the sinkhole doesn't’t surprise him.
“Managing the tunnel-muck consistency is not easy in normal conditions. It is very complex in Seattle because at no time is the [machine] cutting a single type of soil,” he said.
The problem is limited to the area immediately around the machine and has not spread to the nearby Alaskan Way Viaduct, said WSDOT spokeswoman Laura Newborn. This suspension for cause only addresses tunneling operations involving the tunneling machine, including loading of barges at the site. It does not affect any of the other work under the design-build contract with STP or in any other contracts being managed by the viaduct program.
Governor Inslee mentioned a concern many Seattle citizens have expressed - that if STP continues to dig too much soil as Bertha proceeds north, will the viaduct and downtown buildings could be threatened?