Village Creek Tunnel and Pump Station

The pump station and Influent Tunnel were a complex desgin and construction undertaking. Several geological features, including four different formations and contact zones, were mapped within the construction area. Other features complicating the subsurface included thrust faults and steeply dipping beds. The formations included Pottsville, Red Mountain, Knox Group and Conasauga. Each of these formations has completely different geologic characteristics with excavation conditions, stability and groundwater. With a 135' deep pump station and a 70' deep, 10' diameter and 4,000 long tunnel, there were critical design concerns.

BHATE conducted a detailed geotechnical evaluation to define the subsurface and excavation conditions for the Influent Tunnel and the Pump Station. The geologic contacts were mapped along the tunnel alignment. This was an important part of the Influent Tunnel design, since two alternate alignments were being considered. The tunnel excavation, for the most part, was completed with a Tunnel Boring Machine (TBM). Tunnel boring conditons were highly variable, ranging from hard sandstone, soft shale, limestone, clay broken and fractured rock and zones of deep, soft soils with significant ground water conditions.