TBM assembly in progress at Seattle Ship Canal site

10 February 2021

Seattleā€™s Ship Canal Water Quality Project (SCWQP) continues to make progress as TBM assembly for the stormwater tunnel is undertaken on the Ballard site accompanied over the coming weeks by other works.

The US$255m SCWQP contract includes the construction of a 4.32km-long storage tunnel with an internal diameter of 5.74m that will capture and temporarily store around 132bn litres (29m gallons) of combined sewer overflows.

The Ballard site is also seeing the installation of the concrete lining for the 37.2m-deep, 27.4m diameter shaft for lowering of the Herrenknecht TBM. Located at the western end of the tunnel, the site will also be home to the pumping station that will convey water to the treatment plant. On the East Ballard site, soil stabilisation and ground improvement activities are continuing.

There are five shafts on the project. At the Fremont site, crews will excavate a 26m-deep, 9.75m-diameter drop shaft ready for the launch of a smaller TBM. It will bore the 2.43m diameter, 197m-long tunnel (beneath the existing Ship Canal) which will connect two vertical drop shafts at Queen Anne and Fremont.

Construction of a secant pile wall at Wallingford is underway and is anticipated to last through to mid-April. So far, around 10 of the 101 piles have been completed. At the Queen Anne site, shaft excavation continues and crews are expected to pour the concrete base over the coming weeks.

The Ship Canal Water Quality Project is a being built by Seattle Public Utilities and King County Wastewater Treatment Division. The works aim to significantly reduce the amount of combined sewage overflows into local water bodies, including into the Lake Washington Ship Canal, Salmon Bay and Lake Union. The project will be implemented by Lane Construction Corp – the US subsidiary of Webuild Group. Tunnelling is expected to begin in the summer of 2021.