Washington Gov. Jay Inslee has issued an emergency order to stop the tunneling work along Seattle's waterfront.
Contractors found a sinkhole 35 feet long and 15 feet deep near the tunneling machine known as Bertha Tuesday night, the latest of several problems facing the project.
Inslee announced the "stop order" in a news conference Thursday in Olympia.
"The very reason the legislature proceeded with this project was to fundamentally assure public safety. I have great concerns regarding public safety if the contractor were to move forward without addressing the root causes of this sinkhole," Inslee said.
He said Seattle Tunnel Partners can’t restart Bertha until they can explain exactly why the large sinkhole appeared earlier this week. Inslee said work won't resume until the tunnel contractor submits safety and work plans that satisfy a team of independent experts.
Bertha is digging through a mixture of sand and clay. Sometimes, the vibrations will cause pockets of sand to shake loose and just slide into Bertha’s cutterhead, where it’s carried away. That leaves a hole on the surface.
The trick is to catch sinkholes early enough, so that you can quickly inject grout or concrete into the ground and stop the ground from collapsing. The contractor was supposedly carefully monitoring the ground for that kind of event.
“We have a complete picture of what might be moving below ground and above ground as we’re tunneling,” Seattle Tunnel Partners' Chris Dixon said last week in a teleconference.
But according to Inslee, the contractor stopped monitoring the ground at some point. “So frankly, I don’t understand that decision at all,” Inslee said.
The location of the sinkhole was lucky: It happened under the open sky, where it could quickly be filled. The ground there is isolated from the Alaskan Way Viaduct by an underground wall.
But if a big sinkhole were to appear underneath one of the viaduct’s main supports when Bertha is digging under the viaduct in March, that could have much larger consequences.
A Washington State Department of Transportation spokesperson said there is no indication of other sinkholes.
Bertha just resumed tunneling work last month after undergoing mechanical repairs.
The tunnel project is two years behind schedule.