The project is the design-build of a 24,000-foot-long, 26-foot-diameter CSO tunnel constructed in soft ground under and adjacent to the Potomac and Anacostia Rivers. In addition to the tunnel, the project includes a 132-foot-diameter dewatering shaft and a 76-foot-diameter screening shaft at Blue Plains Advanced Wastewater Treatment Plant (BPAWWTP) to serve as main access point for the tunnel construction; a 55-foot-diameter drop shaft at the main pumping station to serve as terminus point; a 50-foot-diameter drop/overflow shaft at Joint Base Anacostia Bolling; and a 55-foot-diameter junction/ drop shaft at Poplar Point Pumping Station. The tunnel lining will be constructed of bolted/gasketed precast concrete segments.
The process of launching a TBM at the start of the drive or passing in and out of intermediate shafts can involve significant risk of ground loss if not managed properly. In order to mitigate this risk, TBI has developed a cut-off wall system outside of the main launch shaft that will provide protection against ground loss. In addition, at intermediate shafts, TBI has developed a risk reduction measure whereby the shafts will be partially backfilled to balance the external ground/groundwater pressures and reduce the risk of inundation.
Market: Water / Waste Water
Service: Underground Construction
Project Value: $305 million
Start Date: 2011
Completion Date: 2015