Constructing Seattle’s Ship Canal Tunnel to Enhance Water Quality
The Ship Canal tunnel underground storage is a 2.7-mile stretch from Ballard to Wallingford. The tunnel will prevent an average of 75 million gallons of polluted stormwater and sewage from entering the waterways each year.
Malcolm Drilling was contracted to install one 210-foot-deep access shaft using a reinforced Diaphragm Wall (D-Wall) to function as excavation support as well as a cut-off wall. All elements were installed within verticality tolerances of less than 0.5%, and overall water infiltration of fewer than 5 gallons per minute for the entire shaft was achieved. Jet Grouting, Secant Piles, and Soldier Beam-Lagging shoring complemented their scope for other near-surface structures of this project.
Positioned at the 11th Avenue and Fremont Drop Shaft Sites, the two jet grout blocks served multiple purposes – acting as a safe haven for the Tunnel Boring Machine (TBM), sealing the Vent Shaft surface connections, and providing stability and groundwater control for the adit excavations. Compaction grouting was also performed by Malcolm on one structure to mitigate liquefaction. To aid the excavation, they also installed several dewatering wells and provided maintenance and removal throughout the project’s construction period.
