Flipping Book | 110 years of future | Salini Impregilo Library

233 The project is part of the Clean River Project, a plan launched in 2010 by the District of Columbia federal authorities and administration to eliminate the risk of introducing untreated sewage into the waterways in the event of exceptionally heavy rainfall (events called Combined Sewer Overflow, CSO). The DC Water and Sewer Authority awarded a contract to the joint venture formed by Impregilo, Healy (a full sub- sidiary company) and other partners for the construction of a 3.8-km long hy- draulic tunnel developing mostly along the Anacostia River, a tributary of the Potomac River. The excavation is performed in mostly soft ground at an average depth of approx- imately 30 m and is carried out using a Tunnel-Boring Machine (TBM) with an excavation diameter of 7.9 m. The ma- chine, weighing around 650 tons, was assembled on the surface and a gantry crane was used to drop it into the under- ground construction site. The project also includes six water intake shafts, approximately 30 m deep with a diameter ranging from 9 to 22 m. The work will be completed by building tun- nels connecting to pre-exisitng infrastruc- ture and other concrete jobs to facilitate aeration, controlling gases and the river water. Particularly innovative for the United States was the decision to use only fibre reinforced precast concrete segments. The tunnel and related hydraulic projects will direct wastewater and rain water sep- arately to prevent the risk of CSO occur- ring by 98%, thus guaranteeing good en- vironmental protection for the Anacostia, Potomac and Rock Creek Rivers. Employer: DC WASA, District of Columbia Water and Sewer Authority Consortium: Impregilo, Parsons and Healy in a joint venture Project Management: Gilbane Co. (Engineering) Anacostia River Tunnel 2013-IN PROGRESS | WASHINGTON, D.C. (USA)