Seattle Tunnel Partners (STP) – the Washington State Department of Transport’s (WSDOT) design-build contractor on Seattle’s SR-99 Alaskan Way Viaduct replacement tunnel project – has completed the walls for a circular shaft that will provide access to repair damage to the main bearing system on the world’s largest TBM, the 57.5ft (17.52m) Hitachi Zosen EPB machine ‘Bertha’.
STP had previously announced that crews would continue to install the underground walls of the access pit throughout August; and last week the contractor notified WSDOT that there was one pile left to install before the circular pit was complete.
Additional piles will be installed near the pit as part of the support system for the modular lift tower – the large crane that will hoist the machine’s 2,000-ton cutterhead and drive unit out of the ground.
Crews will also install several dewatering wells both inside the access pit and inside the enclosed area south of the access pit around the TBM. Prep work is beginning now and crews should have them installed by mid-September. These wells will lower the groundwater inside the enclosed areas to make it easier to move the TBM into the access pit, as well as to excavate the pit.
STP has notified WSDOT that tunneling machine operators will start Bertha in order to check internal systems in preparation for mining into the circular pit. Also, pieces of the three cranes that will be used to lift the cutterhead pieces out of the access pit are continuing to arrive from around the world.
- Late May: Begin building the access shaft’s underground walls.
- Late July through September: Excavate the shaft.
- October: Remove the machine’s cutterhead and begin repairing damage to the seal system and main bearing.
- February 2015: Test machine to ensure it is ready to tunnel beneath downtown.
- Late March 2015: Resume tunnelling.
Seattle Tunnel Partners repair work plan (pdf 4.8 Mb)
Graphics showing access pit construction (pdf 2.5 Mb)
Video of crews building the access pit (view on YouTube)
Video of crews reconfiguring the tunnel launch pit (view on YouTube)
Brochure of STP’s repair plan (pdf 1 Mb).