(WSDOT photo: Crews assembling rebar for a section of the foundation to support northbound SR 99 roadway and wall on west side of roadway)

The Highway 99 tunneling machine is back on the move, and re-aligned after veering a half-foot off course, according to this update late today from WSDOT:

Seattle Tunnel Partners resumed mining today after conducting additional survey work to verify Bertha’s position and to make necessary adjustments to complete the tunnel drive. Crews performed routine inspections and maintenance while mining was stopped, including the replacement of cutterhead tools.

As of this afternoon, Bertha was tunneling north toward the intersection of Denny Way and Sixth Avenue North, less than 1,000 feet from the disassembly pit.

STP stopped mining on February 28 after survey data indicated the tunneling machine may be several inches off the tunnel alignment. Three independent surveys confirmed the 57.5-foot machine was approximately six inches off alignment.

STP designers made a slight change to the tunnel alignment between the machine’s current location and the end of the tunnel drive. Adjustments are common during tunneling, including on this project. STP made a similar adjustment to correct Bertha’s course after the machine mined out of the access pit following repairs.

Crews steer Bertha based on information they receive from its on-board guidance system. The system is now set to the new tunnel alignment. According to STP’s most recent schedule, Bertha will arrive at the disassembly pit in May.