It took years for Bertha, a tunnel-boring machine, to mine 1.7 miles underneath downtown Seattle, but crews will spend just five months removing the 57.5-ft-dia machine from the receiving pit near Seattle’s Space Needle.
Bertha mined into place in April, having completed its mission to bore a tunnel for a double-decker road that will eventually replace the city’s aging Alaskan Way Viaduct. With the work of Bertha done, the crew working on the machine had one more task: cut up Bertha and lift it out of the pit.
The first piece of Bertha was removed in early May, as crews cut a small piece of the machine’s shield to confirm its sectional weight ahead of cutting and lifting other pieces. To disassemble the 900-ton cutterhead, crews will perform 35 lifts with cranes in a process that will last five months.
For a video of the operation, check out the Washington State Dept of Transportation’s recently released video here.
So far, three of the cutterhead’s eight small spokes have been cut and lifted from the pit. To pull off the lifts, workers much cut the steel that connects the cutterhead’s 16 spokes and welding lifting eyes onto the spokes so they can be safely hoisted by the on-site 400-ton crane.
Many of the workers now helping disassemble the tunneling machine are the same workers who built the tunnel.
The entire process can be monitored with the WSDOT time-lapse construction camera positioned on site.
With the cutterhead pieces getting lifted from the disassembly pit by crane, other pieces will get removed from the tunnel through the south end, where the mining started. Along with the remainder of the 326-ft-long machine, crews will need to haul away more than 20 miles of pipe, ventilation duct and the machine’s conveyor belt.
At the same time, work continues inside the tunnel to build the roadway and have the project open to traffic in 2019, four years after the originally planned date.
Follow Tim Newcomb on Twitter at @tdnewcomb.