Alaskan Way Viaduct Replacement contractor, Seattle Tunnel Partners has temporarily stopped mining to prepare Bertha, the 17.52m diameter Hitachi Zosen EPBM SR 99 tunnelling machine, for the final 308m (1,000 feet) of the 2.7km long (9,270-foot) tunnel drive.
Crews stopped mining on 28th February to verify Bertha’s position along the tunnel route before making their final push to the disassembly pit. Recent surveys show that Bertha may be several inches off of the tunnel alignment. STP is conducting additional survey work and will make adjustments as needed to complete the tunnel drive.
STP made a similar adjustment to correct Bertha’s course after crews mined out of the pit that was used to access and repair the machine.
Crews will continue to perform routine maintenance on the machine for the next several days. They plan to resume mining next week.
According to STP’s most recent schedule, Bertha will arrive at the disassembly pit in May. The pit is located approximately 292m (960 feet) north of the cutterhead’s current location beneath Denny Way and Sixth Avenue North. Mining rates will continue to vary based on maintenance needs and soil conditions.
Crews successfully mined under the final building of the tunnel drive earlier this week. Bertha has built 1,270 of 1,426 concrete tunnel rings.