By Ashley Karen
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) started in 2011 to fulfill Clean Water Act standards and manage water quality problems.
The Shoreline Storage Tunnel is the fifth of seven new large-diameter tunnels, along with further projects, that NEORSD will employ toward Project Clean Lake’s general objective to decrease the 4.5 billion gallons [17 billion liters] of wet weather combined sewer overflows (CSOs) discharged into Lake Erie and its tributaries in the Greater Cleveland area.
The Tunnel incorporates 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 catch and keep overflows from CSO outfalls along the Lake Erie shoreline. Ten, the SST will transfer these overflows to other NEORSD tunnels and sewers which will convey flows to the Easterly Wastewater Treatment Plant for treatment before they are discharged into the environment.
SST construction was granted to the McNally/Kiewit SST JV. NEORSD published a statement to proceed in July 2021 with an expected substantial completion date of January 2026.
After delivering overall design management, containing tunnel and shaft design and geotechnical engineering, Delve Underground has transitioned from the design phase to the construction phase. Three Delve employees are on-site currently, delivering construction management services for NEORSD.
The shaft final lining collar work, SOE (shaft support of excavation), shaft excavation, and the geotechnical instrumentation installation are all finished. Nicholson Construction Company assembled for the project from August 2021 to November 2022 to finish the cement bentonite wall SOE for the near-surface structures, cement bentonite ground improvement zones for TBM break-in and break-out locations, and slurry diaphragm walls for the shaft SOE at all three shaft sites. Northstar Contracting was chosen as a subcontract to complete all concrete work on the project. Now, Northstar is pouring the final lining at the SST-2 site before moving on to the SST-3 shaft.
The tunnel is bored with a 26-ft diameter (8-m) Herrenknecht EPM TBM (earth pressure balance tunnel boring machine) with a face pressure near 3.5 bar.
McNally/Kiewit (MK) designed a 6-ft long (1.8-m) tunnel ring lining that consists of five precast segments as well as one keystone for the final lining. Presently, the tunnel boring machine is halfway through the second reach and has successfully excavated through the most challenging ground along the alignment (a mixed face with the potential of boulders up to 48 in. [1,220 mm]). MK should end excavation and TBM disassembly before this time next year.
The other work to be achieved by the end of the project comprises the near-surface structure works at each site; the internal concrete for two baffle drop shafts and one tangential drop shaft; one new regulator structure; three regulator modifications/repairs; the procurement, installation, and testing/commissioning all of the gates and controls; and site restoration work.
