Differential settlement of more than an inch has temporarily shut down efforts on the already-stalled Alaskan Way Viaduct project under downtown Seattle. Excavation had been underway on an access pit that was designed to repair "Bertha," the stuck tunnel-boring machine (TBM), as crews continue to monitor the movement on surrounding buildings.
The 57.5-ft-dia machine has been stuck since December 2013, just over 1,000 ft into its 1.7-mile route under downtown Seattle as part of an effort to replace the aging viaduct after settlement was first detected a month earlier (ENR 2/24 p. 21).