Mammoet Lowers TBM Parts Back Down the SR99 Pit

Mammoet has lowered the front end of the repaired tunnel boring machine, Bertha, into the access pit in Seattle. Bertha has been undergoing repairs since March when Mammoet lifted parts of the damaged TBM to the surface for repairs. Bertha's seals were damaged in 2013 after tunneling just 1,000 feet as part of Seattle Tunnel Partners' SR99 project.

Since Mammoet successfully raised the front end in March, the bearing block section of the boring machine has been undergoing renovation. The inner and outer bearings, surrounding the drive ring, have been replaced with bearings with stiffer seals. With the repair work to this part of the machine complete, it needed to be reunited with the rest of the cutter head for the next phase of the machine’s recovery, Mammoet said in a statement.

On August 15, Mammoet lifted the 370-tonne bearing block onto the cutter head for reassembly. Further reconstruction work was then necessary when 16 of 24 electric motors, each weighing 13 tonnes, had to be reattached before the cutter head could be maneuvered down for reconnection with the main portion of the tunnel boring machine. In total, a load of 1814.37 tonnes, which includes the circular bearing block and round cutter head, was rotated a quarter turn and lowered back into the 120-foot deep access pit.

Following the lowering of the heavy machine cutter, crews are working to reconnect all sections of the machine. Once reassembly is completed, tests will be done to certify that tunneling may begin again.