WSDOT says the TBM is digging well below the area’s "notorious fill soil." The top of the machine is approximately 80ft below the surface in a mixture of glacially compacted material.
Currently, STP has two tunneling crews consisting of approximately 25 members each. Each crew is working six, 12-hour shifts per week. According to STP’s most recent schedule the TBM is expected to reach a planned underground maintenance stop in late January. Once there, crews will spend approximately three weeks performing final maintenance before the machine tunnels beneath the Alaskan Way Viaduct.
WSDOT will fully close SR 99 through downtown Seattle for approximately two weeks while the machine passes beneath the viaduct.
