Specialty Jet Grouting and Deep Mixing for DC Clean Rivers

The Clean Rivers Project is DC Water’s ongoing program to reduce combined sewer overflows into the District of Columbia’s waterways; being the Anacostia and Potomac Rivers and Rock Creek. The Project is a massive infrastructure improvement designed to capture and clean water during heavy rainfalls before it ever reaches the public waterways. To create the massive underground structures that form the solution to combined sewer overflows (CSOs), tunnel boring machines are being used to excavate tunnels more than 100 feet underground. Known as the Blue Plains Tunnel, this first section of tunnel is a 4-mile reach of the 13-mile Anacostia River Tunnel, stretching from the blue plains waste water treatment plant, to the Main Pumping Station in downtown, Washington, D.C. Along the route of the Blue Plains Tunnel is the largest advanced wastewater treatment plant in the world, the TBM launch shaft, retrieval shaft, several drop shafts (around which pumping stations are to be constructed), and numerous diversion sewers and ancillary structures to complete the massive CSO infrastructure system. At each of these locations, various forms of ground modification/ground improvement were performed, including independent SOE systems, support for micro-tunneling operations, ground-water control, utility protection, and settlement protection. This paper discusses the challenges and solutions for this specialty work.