Speaker: Jewels Stover, Nicholson Construction

The Westerly Storage Tunnel (WST) Project is part of Project Clean Lake, the Northeast Ohio Regional Sewer District's program designed to reduce pollution in Lake Erie by 4 billion gallons over the next 25 years. When completed in 2020, WST will be nearly 2 miles of 25-ft diameter tunnel installed 200-250 ft below ground. The storage tunnel will manage higher flow volumes, reducing stormwater influx in the combined sewer system and reducing overflow occurrences. The project required three deep shafts to access the tunnel, one each at the launch and retrieval sites for the TBM and a third for a vent shaft. Support of excavation for the access shafts was constructed utilizing unreinforced diaphragm walls. This innovative, value-engineered alternate significantly reduced risks associated with traditional secant piles combined with a rib and liner plate system. Implementation of the diaphragm wall technology resulted in a water tight, continuous shaft keyed into rock. This case study and presentation will examine the design, methodology, installation approach, and challenges unique to each deep shaft.