ROADS/BRIDGES: Seattle’s S.R. 99 given a completion date as digging resumes

Tunnel-boring machine “Bertha” is headed back to work by late fall

July 20, 2015

According to an announcement by Washington state transportation officials, work on the beleaguered State Route 99 tunnel will resume on Nov. 23, with the boring machine known as “Big Bertha” set to emerge at the north end of the city’s downtown area approximately one year thereafter.

Moreover, officials say the S.R. 99 tunnel is now scheduled to open to drivers by spring 2018. This comes almost three years behind the original target of late 2015. Several hiccups in progress had lead to this protracted timeline.

Crews stopped tunneling in Dec. 2013 after Bertha overheated, after which an investigation discovered damage to the seal system that needed to be replaced along with the main bearing. Then crews spent most of 2014 digging a pit to access the front of the machine so the cutter head could be repaired.

Seattle Tunnel Partners pulled the machine out of the ground in March of this year. STP announced this week that installation had begun for a new main bearing on the machine.