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SR 99 TBM nears return to access pit

Contractor Seattle Tunnel Partners (STP) is preparing to lower the repaired front end of the SR 99 tunnelling machine back into the access pit.

Progress on the Alaskan Way Viaduct replacement project was delayed when tunnel boring machine (TBM) Bertha stalled in December 2013 due to overheating.

Much of the repair and reassembly work is now complete. STP is awaiting the arrival of rollers and cages, which are part of the machine’s new main bearing.

STP chose to remanufacture some parts because of tight tolerances – measured in millimeters – that need to be met as the machine is reassembled.

STP has indicated the lowering of pieces into the pit will now occur two weeks later than the date shown on its most recent schedule. The contractor expects to resume tunnelling in late November as scheduled.

Crews from Mammoet, the firm that built and operates the modular lift tower (MLT), will begin running tests of the crane next week.

When the MLT and the machine are ready, Mammoet will use the crane to reassemble the machine’s front end at the surface.

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