Decades of continuous service of large-diameter buried pre-stressed concrete cylinder pipelines (PCCP) has led to deterioration that threatens the structural integrity of these pipelines. In late 2014, Washington Suburban Sanitary Commission (WSSC) contracted with an inspection company consultants, Pure Technologies, to assess the condition of thousands of feet of below ground 66-in. PCCP. Performing an electromagnetic survey, consultants detected significant, accelerating prestressing wire break activity on a single section of PCCP, indicating a high likelihood of failure. This pipe was less than 25 ft from an active industrial and commuter railroad.
Once this pipe was dewatered, a subsequent visual inspection was performed and multiple longitudinal cracks were identified. Removing and replacing this damaged 20-ft section would be challenging, cost-prohibitive and could significantly compromise the train schedule for a long duration. Faced with these challenges, the owner decided to internally line the deficient pipe section with a Carbon Fiber Reinforcement Polymer (CFRP) System manufactured by Fyfe Company, which is a specialized carbon fabric that is saturated with polymers and used for strengthening pipelines, structures and infrastructure.
This alternative repair method has been accepted in the municipal pipe industry for failing pipe sections and emergency applications that afford a shortened construction schedule, minimal curing time and immediate return to service conditions and pressures.
City of Baltimore Department of Public Works Sanitary Contract (SC) 875: Rehabilitation of Southwest Diversion Pressure/Gravity Sewer – Phase III
The SC 875 project involved the rehabilitation of the 78-in. diameter Southwest Diversion Sewer and the connecting 27-in. diameter Maidens Choice Pressure Sewer. Approximately 2,551 lf of 78-in. diameter reinforced concrete pipe (RCP) was rehabilitated with CIPP lining; approximately 2,124 lf of 78-in. diameter pre-stressed concrete cylinder pipe (PCCP) was rehabilitated with a carbon fiber reinforced polymer (CFRP) lining; and approximately 384 lf of the 27-in. diameter Maidens Choice Pressure sewer was rehabilitated with a pressure-rated CIPP lining.
Also as part of the project, seven manholes and one bar screen structure that was the convergence of the upstream 54-in. and 66-in. sanitary sewers to the 78-in. In order to complete the rehabilitation of the sewers and the structures, a bypass pumping system had to be set up and operated throughout the course of the rehabilitation. This included eight 24-in. diameter HDPE bypass pipes that were routed a total of 5,600 lf around the repair area. Also sixteen 18-in. pumps were set up to bypass the flow (three being stand-by pumps) from the SWDS, and four 8-in. pumps to bypass the flow (one being a stand by-pump) from the Maidens Choice Pressure Sewer that connects into the SWDS. Spiniello was the prime contractor for the project. Sunbelt was the contractor that completed the bypass pumping and Structural Technologies performed the CFRP lining.