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STP Readies for Bertha

A view of the 120-ft deep pit crews will use to access and repair Bertha, the SR 99 tunneling machine. Photo from the Washington State Department of Transportation.

A view of the 120-ft deep pit crews will use to access and repair Bertha, the SR 99 tunneling machine. Photo from the Washington State Department of Transportation.

Seattle Tunnel Partners (STP) is making final preparations for Bertha’s move into the 120-ft deep pit that will allow crews to hoist the machine to the surface for repairs, according to the Washington State Department of Transportation website. STP’s final preparations included injecting grout into the ground and installing new drains alongside the machine. These measures will help crews control groundwater as Bertha slowly moves forward through the wall of the pit.

According to the Associated Press, drilling resumed on Feb. 17 and advanced 6 ft over the next day. The TBM must advance a total of 20 ft to reach the access pit.

Crews plan to use heavy equipment to chip away the portion of the pit’s southern wall where Bertha will eventually emerge. This process is similar to scoring a surface before you cut into it, and will allow the concrete to break away in a controlled manner when Bertha finally moves into the pit.

Approximately 20 ft of unreinforced concrete stands between Bertha and daylight. The duration of Bertha’s dig will depend on her ability to mine through and digest concrete while operating with a damaged seal system. STP expects Bertha to overheat, as she has during their most recent attempts at mining. They will likely mine until the machine becomes too hot, then take a break. To speed up the move, crews may choose to continue chipping their way toward Bertha from within the pit during times when the machine is cooling off.

Moving Bertha into the pit is just the beginning of the repair process. The machine must be partially disassembled before it can be lifted to the surface, a process that will likely take significant time and effort.

Meanwhile, at the SR 99 tunnel’s north portal, STP is continuing with its investigation of the safety incident involving five ironworkers who were installing rebar for a concrete wall on Feb. 12. STP is thankful that four of the workers were not seriously injured. The fifth worker is currently receiving medical treatment at Harborview Medical Center. While work is proceeding at the north portal, it is not proceeding in the area where the workers were injured, as the investigation of the safety incident is ongoing. STP is very proud of its safety program and safety record on the SR 99 Tunnel Project, which focuses on creating safe work conditions and eliminating unsafe work practices and at-risk work behaviors. STP takes every safety incident very seriously. As with every safety incident, STP will investigate this safety incident to determine the cause(s) and to identify the corrective action(s) to be implemented to prevent the reoccurrence of the same or similar safety incident in the future.

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