The project
Reinforced Diaphragm Slurry Walls provided initial support during shaft excavation and also formed part of the permanent structure.
The DC Clean Rivers Project Division A - Blue Plains Tunnel is one of several contracts that comprise the overall Long Term Control Plan (LTCP) of DC Water, which consists of a network of new tunnels, sewers, and diversion structures designed to capture overflows to Rock Creek, and the Anacostia and Potomac rivers for treatment at the Blue Plains Advanced Waste Water Treatment Plant.
The challenge
DC Water is in the process of implementing its LTCP to meet requirements established by the US Environmental Protection Agency for pollution control and reduction of combined sewer overflows into nearby waterways.
The solution
Keller was contracted to design and install 5 reinforced concrete slurry diaphragm wall shafts along the tunnel alignment. The slurry walls provided initial support during shaft excavation and also formed part of the permanent structure. Two of the shafts were combined in a figure-8 configuration, consisting of a 76-foot diameter screening shaft and a 132-foot diameter dewatering shaft approximately 170 to 190 feet deep. These two shafts also served as the main access point for the tunnel construction. Soil conditions included fill, alluvium, and very stiff to hard silt and clays.