Bertha, the SR 99 TBM, is now tunneling in Seattle soil after breaking through the access pit wall on the 06.01.2016. Seattle Tunnel Partners has mined more than 22 m and installed 12 concrete tunnel rings since Bertha first moved forward in the pit on 22.12.2015. She is now approaching South Main Street, near Pier 48, Bertha is digging well below the area’s notorious fill soil. The top of the machine is approximately 24 m below the surface in a mixture of glacially compacted material. Bertha is expected to reach a planned underground maintenance stop, approximately 137 m to the north, just south of Yesler Way 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 for approximately two weeks while the machine passes beneath the viaduct. STP’s latest projections show that the closure will occur in March. Click here and us/69 for the tunnelbuilder archive. Visit http://www.wsdot.wa.gov/. 01/16.