The Shoreline Storage Tunnel (SST) Project is part of the District’s Long-Term Control Plan to control and reduce combined sewer overflows (CSOs) into Lake Erie. It is the District’s first major soft-ground CSO tunnel and is being constructed in an urban environment with many varied stakeholders. The tunnel is being excavated using an earth pressure balance (EPB) tunnel boring machine (TBM) with face pressures near 3 bar.
The project includes 14,120 linear feet (4,304 m) of 23-foot-inside-diameter (7 m) CSO storage tunnel, along with three in-line deep shafts with finished diameters ranging from 40 to 61 feet (12.2 to 18.6 m) and bottom of excavations down to 133 feet (40.5 m) below ground surface. Significant near-surface structures include diversion, gate, and screening structures ranging from 22 to 47 feet (6.7 to 14.3 m) deep in weak soil conditions with high groundwater tables. The SST will drain by gravity into a drop shaft on the Dugway Storage Tunnel.
Delve Underground was the prime consultant for the project. In addition to overall management of the design team, we were responsible for evaluating tunnel alignment alternatives, geotechnical engineering, tunnel and shaft design, TBM specification, and settlement impacts to existing adjacent structures.
The project is currently under construction and is anticipated to be completed in early 2026. The Delve Underground team is providing design support services during construction, including an on-site resident project representative and TBM excavation oversight monitoring.
A unique aspect of the SST Project design scope was that it included hydraulic integrated catchment modeling and surge modeling for the entire SST and Shoreline Consolidation Sewer (SCS) System, which required significant coordination between the Delve Underground team and the SCS designer.