DC Water’s celebrated TBM – dubbed “Lady Bird” — has completed its mission, creating a four-and-a-half-mile-long tunnel that will be used to help improve the water quality in the Anacostia River. Tunneling was completed earlier this month and on July 23 the 26-ft diameter cutterhead was extracted from a 100-ft deep shaft near DC Water’s Main Pumping Station in Southeast Washington, D.C.
Tunneling began in July 2013 from a starting point at the Blue Plains Advanced Wastewater Treatment Plant. The TBM tunneled along the Potomac River northward to Poplar Point and then crossed under the Anacostia River and continued west, finishing at a deep shaft along Tingey Street, SE. To prepare for the TBM’s arrival, this shaft was filled with flowable fill concrete and water, to protect against changes in pressure as Lady Bird mined through the shaft wall. Crews then dug out the concrete to reveal the machine.
“This is a terrific milestone for DC Water’s Clean Rivers Project,” said DC Water CEO and General Manager George S. Hawkins. “We are fortunate that the tunneling went so smoothly, finishing on time and on budget, and I applaud our DC Water staff as well as Traylor/Skanska/Jay Dee and everyone else who took part in this successful dig.”
DC Water’s Clean Rivers Project will incorporate two methods to keep combined sewage and stormwater from overflowing into waterways, during heavy rains in the parts of the city with a combined sewer system. The first is to build underground tunnels that will hold combined sewage and stormwater until rain subsides, then convey it for treatment at Blue Plains. The second is to create green infrastructure to capture and infiltrate rain on-site before it can reach the combined sewer system.
Carlton Ray, Director of the DC Clean Rivers Project, added “Lady Bird performed as well as projected—having a one-day best mark of 150 ft. In her best week, she tunneled 631 feet. This TBM’s success means we are one step closer to a cleaner Anacostia River.”
Lady Bird dug the southernmost segment of the Anacostia River Tunnel. The next section will be mined by another TBM named Nannie, who is preparing to begin her tunnel at a site near RFK Stadium. The Northeast Boundary Tunnel is the longest portion of tunnel, and that contract has yet to be awarded. At the northern tip of the tunnel system is the First Street Tunnel, a relatively short tunnel that will be mined by Lucy, and is designed as a flood protection project for the Bloomingdale and LeDroit Park neighborhoods.
Lady Bird removed approximately 1.2 million tons of material. This was hauled away in nearly 72,000 truckloads over the last two years. The tunnel was built with 28,189 pre-cast concrete segments which made up 4,027 full rings. The TBM is being sold back to German manufacturer, Herrenknecht.