DC Water Anacostia Force Main Emergency Repair

After reporting odor leakage, a DC Water engineer confirmed a 10-ft long missing section of concrete and steel cylinder at the crown of the 108 in. diameter Anacostia pressurized sanitary sewer force main. Made of pre-stressed concrete cylinder pipe (PCCP), the Anacostia main also showed areas of distress adjacent to the 10-ft missing section. When excavated to the springline, it was determined that the entire segment of the pipe was deteriorated. The crown section of pipe wall, including the interior mortar lining and steel cylinder, were no longer intact. Due to the critical nature of the line, live flow had to be maintained during the repair. The repair was design for internal pressure and external loads. The repair was performed in several steps including first patching the missing concrete core and steel cylinder using a sulphate resistant concrete to restore the host pipe. A shotcrete encasement was placed over the initial pour that repaired the continuity of the host pipe. A full reinforced concrete encasement was designed and placed to resist the internal pressure from typical force main operations. The encasement utilized micropile tie downs to resist uplift forces from the internal pressure because the pipe could not be excavated around the perimeter due to high ground water and daily surge of sewage. The entire repair was designed and completed with crews working around the clock.