Rehabilitation of 78-inch PCCP with Carbon Fiber Reinforced Composite Material

摘要

Calleguas Municipal Water District initiated their Infrastructure Reliability Program (IRP) in 1997 after repairing a catastrophic failure of a 66-inch diameter prestressed concrete cylinder pipeline (PCCP). The IRP includes tasks to assess the condition of the existing PCCP in order to prioritize and rehabilitate deteriorating sections of the transmission system. Condition assessments have been conducted using visual inspections, acoustic techniques, and remote field eddy current/transformer coupling testing equipment on approximately 5 miles of the system. Forensic studies conducted on the damaged pipe indicated that the failure was probably the result of hydrogen embrittlement of the prestressing wire induced by an impressed current cathodic protection system. Pipe rehabilitation was prioritized and sections of 78-inch and 66-inch pipe were replaced in 1998 and 1999.The District's rehabilitation program was expanded for the winter of 2000 to include lining approximately 1,100 feet of the most significantly damaged pipe with steel plate liners. However, two 20-foot sections of severely deteriorated pipe, at two different locations, were not accessible for the steel lining operation. Rather than excavate each section of pipe and replace itwith a new section of welded steel pipe, the District decided to line the two sections of pipe using a carbon fiber-reinforced composite material. Carbon fiber composites are a relatively new material for pipeline rehabilitation. The material replaces the deteriorating structural components of the PCCP with a composite material of epoxy resin reinforced with high tensile strength (110,000 psi) carbon fiber. The thin composite section (0.25 inches) is directly applied to the inside of the PCCP in multiple layers.In February 2000, the District awarded a design/build contract to rehabilitate two twenty-foot sections of 78-inch diameter PCCP using carbon fiber-reinforced composite material. The primary reasons for rehabilitating the sections with the composite material included: 1) the repair could be accomplished using existing manways for access to the pipeline, thereby avoiding the expense of excavation, shoring, and demolition of the PCCP; 2) the lack of excavation minimized impacts to the public, traffic, adjacent utilities and structures, and eliminated the need to acquire temporary right of way to conduct the repair; and 3) the composite lining could be installed quickly.The design/build project for installing the carbon fiber-reinforced composite proceeded smoothly with little disruption to the public and no impacts to adjacent utilities or structures. The total cost for the repairs was approximately equal to the cost for excavation and replacement of the PCCP. The District's approach to PCCP assessment and rehabilitation and their willingness to use an innovative rehabilitation method resulted in their having a viable alternative for PCCP rehabilitation.