The tunnel-boring machine Bertha broke through its concrete access vault and is now tunneling beneath Seattle on its way toward a planned maintenance stop, the Washington Department of Transportation (WSDOT) said in a statement.
The Highway 99 tunneling machine, now approaching South Main Street, has moved approximately 73 ft since it was repaired last month before the restart.
Bertha will dig another 400 ft until it reaches its planned maintenance stop, where it will be inspected for about a month. It will then begin tunneling again in March for 24 hours a day, seven days a week with crews working two 12-hour shifts, seven days a week.
Both the closure and the expedited digging are precautionary to allow better monitoring of the site and lessen any chance of settling, Dixon and WSDOT's Project Administrator Todd Trepanier said.
Once the machine starts tunneling underneath the Alaskan Way Viaduct, WSDOT will close Highway 99 in downtown Seattle for two weeks.
WSDOT is confident the boring machine won't encounter any more problems, but if it does while under the viaduct, crews will have to make the repairs underground.
