By Lynda Myer
Digging the storage tunnel, TBM MudHoney has broken through on Seattle’s Ship Canal Water Quality Project.
In order to preventing groundwater flowing in, the EPBM with 5.4m diameter has tunnelled 4.25km from Ballard to Wallingford, where it emerged in a flooded shaft. Following installation of the last few tunnel segments by MudHoney, the shaft is due to be emptied and crews will dismantle the TBM.
TBM Bertha, which is 2.4m diameter and remote-controlled and excavated the conveyance tunnel, completed work earlier this year and concrete was injected around the shaft to hamper the flow of groundwater, while for TBM MudHoney the limited working space meant flooding the shaft was a better solution.
The last days of the current year is determined date for excavation of a second conveyance tunnel.
Considering that for halting 284 million liters of stormwater and sewage flowing into the Lake Washington Ship Canal, Salmon Bay, and Lake Union each year, Seattle Public Utilities and King County Wastewater Treatment Division’s Ship Canal Water Quality Project is designed, the responsibility of the new tunnel will be capturing and temporarily storing more than 110 million liters of untreated stormwater and sewage during a heavy storm, until the treatment plant can accept it.
In order to collecting stormwater and sewage flows from each basin and sending them almost 12-25m beneath ground into the new storage tunnel, there are five vertical shafts over the 4.25km tunnel path at Ballard, East Ballard, Fremont, Queen Anne, and Wallingford.
Linking the vertical shafts in Queen Anne and Fremont, the conveyance tunnel is located under the Ship Canal. For the final piece of the Seattle Water Storage Tunnel project, new pipes will be installed to connect the existing sewer systems to the new shafts.
