Shoreline Storage Tunnel Shafts and Near Surface Structures Support of Excavation-Paper

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The Shoreline Storage Tunnel (SST) is part of the Northeast Ohio Regional Sewer District’s Project Clean Lake, a long-term program to reduce combined sewer overflows into Lake Erie. The 14,100-ft tunnel in Cleveland is 23 ft in finished diameter and was excavated through soft clays, silts, and fine sands. Its construction required three deep shafts and several near-surface structures (NSS) to launch and retrieve tunnel boring machines and connect existing sewers.<br /><br />Nicholson Construction built the support of excavation (SOE). The three shafts used unreinforced concrete slurry-wall panels, selected in place of secant piles to provide full-depth support while reducing construction risk, schedule, and cost. At SST-1, the wall was keyed into shale; at the other shafts, deeper wall embedment helped control groundwater and basal instability. Cement-bentonite ground-improvement panels were installed at the TBM entry and exit zones. The NSS used soldier-pile reinforced cement-bentonite walls with internal bracing.<br /><br />Construction challenges included verticality deviations in SST-1’s ground-improvement panels, which were repaired with additional panels. At SST-3, a slurry-wall panel collapsed during concreting, likely because groundwater pressure was higher than anticipated. After unsuccessful re-excavation attempts, dewatering wells and a small hydromill enabled completion. Work at one NSS site also required careful coordination around traffic on a busy four-lane road.<br /><br />The shaft walls met the specified water-inflow criterion, and the SOE work was completed on schedule and within budget by the end of 2022. The project applied experience from earlier Project Clean Lake work and advanced construction of the larger program to reduce sewer overflows and pollution in Lake Erie.

Keywords

Shoreline Storage Tunnel

Project Clean Lake

combined sewer overflows

Lake Erie

support of excavation

slurry-wall panels

ground improvement

deep shafts

tunnel boring machines

dewatering wells