Northeast Ohio Regional Sewer District’s Shoreline Storage Tunnel

Northstar Contracting tying rebar at the SST-2 Shaft before advancing the formwork for the next final lining pour.

The Shoreline Storage Tunnel (SST) project is part of Project Clean Lake, a $3 billion, 25-year program that the Northeast Ohio Regional Sewer District (NEORSD) began in 2011 to meet Clean Water Act standards and address water quality issues. The SST is the fifth of seven new large-diameter tunnels, along with other projects, that NEORSD will use toward Project Clean Lake’s overall goal to reduce the 4.5 billion gallons [17 billion liters] of wet weather combined sewer overflows (CSOs) released into Lake Erie and its tributaries in the Greater Cleveland area.

The SST includes nearly 3 miles (4.8 km) of 23-ft diameter (7-m) soft ground tunnel 75 to 140 ft (23 to 43 m) below ground that will capture and store overflows from CSO outfalls along the Lake Erie shoreline. The SST will then convey these overflows to other NEORSD tunnels and sewers, which will transport flows to the Easterly Wastewater Treatment Plant for treatment before they are released into the environment.

Construction of the SST was awarded to the McNally/Kiewit SST Joint Venture. NEORSD issued notice to proceed July 2021 with an anticipated substantial completion date of January 2026. After providing overall design management including tunnel and shaft design and geotechnical engineering, Delve Underground has transitioned from the design phase to the construction phase. Presently, three Delve employees are on site providing construction management services for NEORSD.

Shaft support of excavation (SOE), shaft excavation, the shaft final lining collar work, and the geotechnical instrumentation installation are all complete. Nicholson Construction Company mobilized to the project from August 2021 to November 2022 to complete the cement bentonite ground improvement zones for TBM break-in and break-out locations, cement bentonite wall SOE for the near surface structures and slurry diaphragm walls for the shaft SOE at all three shaft sites. Northstar Contracting was subcontracted to perform all concrete work on the project. Currently, Northstar is pouring the final lining at the SST-2 site before moving on to the SST-3 shaft.

The tunnel is being excavated with a 26-ft diameter (8-m) Herrenknecht earth pressure balance tunnel boring machine (EPM TBM) with a face pressure near 3.5 bar. McNally/Kiewit (MK) designed a 6-ft long (1.8-m) tunnel ring lining that is made up of five precast segments plus one keystone for the final lining. Currently, the TBM is halfway through the second reach and has successfully mined through the most difficult ground along the alignment (a mixed face with the potential of boulders up to 48 in. [1,220 mm]). MK should complete excavation and TBM disassembly before this time next year.

The other work to be completed by the end of the project includes: the internal concrete for two baffle drop shafts and one tangential drop shaft; the near-surface structure work at each site; one new regulator structure; three regulator modifications/repairs; the procurement, installation, and testing/commissioning all of the gates and controls; and site restoration work.

This update was written by Ian Danielson and posted on the Delve Underground website.

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