Mill Creek Tunnel, Contract 3

OWNER: Northeast Ohio Regional Sewer District

SOUTHLAND HOLDINGS TEAM:  Mole Constructors, Inc.


This project included the excavation of 14,775 lf of 23-ft, 8-in diameter tunnel for a sanitary sewer through shale and 470 lf of 10-ft diameter tunnel through shale including shaft excavations to depths of 320 vertical feet. Tunnel excavation was performed using a Robbins TBM for the 23-ft, 8-in diameter tunnel and via a Scotty TBM or Alpine Roadheader for the 10-ft diameter tunnel. The initial tunnel support was steel ribs and wood lagging for larger tunnel and rock dowels for the smaller tunnel. The final lining is a 20-ft diameter reinforced, cast-in-place concrete. The shafts were supported via liner plates within the soft ground, rock dowels, welded wire fabric, and shotcrete within rock. Tangential approach flow, baffle-type flow, and standard drop structures are to be constructed within the shafts. The excavation of the tunnel was delayed during construction for approximately nine months due to the unexpected infiltration of methane gas. The change order amount reflects that change in the environment.