Bertha work causes viaduct, nearby buildings to sink

The Alaska Way Viaduct has sunk a tenth of an inch, but it’s not concerning the Washington State Department of Transportation.

The viaduct has sunk because crews have been pumping groundwater out of the soil in front of Bertha, the tunnel boring machine, in order to figure what’s blocking her path.

“We’ve lowered the water tables sufficiently enough so that we can get in under there under atmospheric conditions and the guys can explore the cutter head,” WSDOT’s David Sower’s explained to KING 5.

Lowering the water table also lowers the viaduct as well as some nearby buildings.

Sowers said the viaduct has already settled over its lifetime, and a tenth of an inch is negligible in terms of the stresses on the viaduct and how the viaduct would behave.

“When the viaduct is moving that much – we don’t see any reason to close it,” Sowers said. “At this time there’s no risk to the public there’s no risk to the structure at the moment.”

KIRO Radio’s Frank Shiers contributed to this report.