Mill Creek Interceptor – Contract 2

Completed in 2004 by Mole Constructors, the Mill Creek Interceptor – Contract 2 consisted of the excavation of 13,200 linear feet of 23 ft 8-inch diameter tunnel for a sanitary sewer through shale and 2,015 linear feet of 10 foot diameter exploratory tunnel through shale including shaft excavations to depths of 200 vertical feet. Tunnel excavation performed via a Robbins Tunnel Boring Machine (TBM) for the 23 foot 8-inch diameter tunnel and via a Lovat for the 10 foot tunnel. The initial tunnel support consisted of steel ribs and wood lagging for the larger tunnel and fiberglass rock dowels for the smaller tunnel. The shafts were supported via ground freezing or liner plates within soft ground, and rock dowels, welded wire fabric and shotcrete within rock. Tangential approach flow, baffle-type flow and standard drop structures were constructed within the shafts.