Inspecting and Repairing Large-Diameter PCCP in a Single Outage

Santa Clara Valley Water (Valley Water) owns and/or operates more than 150 mi of essential large-diameter water conveyance pipelines that provide water to the San Benito and Santa Clara Counties. Valley Water regularly inspects its critical pipelines as a part of their ongoing condition assessment program. Due to the high demand for water and a lack of redundancy, the pipelines can only be shut down for a short period of time during the winter months. As a result, the time for dewatering, inspections, repairs, and recharging must be condensed into a relatively short time frame, about 8−16 weeks, depending upon the overall scope of the project. Analyzing the internal visual, sounding, and electromagnetic (EM) inspection results, selecting the pipes for repair, and implementing repairs in a single outage requires significant planning and coordination from the owner, engineers, consultants, and contractors. To expedite the analysis and repair determinations, criteria that would necessitate repair are established prior to inspection. For prestressed concrete cylinder pipe (PCCP), the criteria are based on the number of contiguous wire breaks detected by electromagnetic inspection and observations made during the internal visual and sounding inspection. Failure risk analysis and repair prioritization determine the most critical pipes for repair. To expedite repairs, worst-case carbon fiber reinforced polymer (CFRP) liners are designed and bid as a supplemental bid item prior to the pipeline inspection to allow for the specialized repair subcontractor to be procured and to perform the repairs as soon as the pipes are identified. This paper presents the overall approach and the results of two case studies with successful implementation of the expedited process of inspection, analysis, and repairs within the allowable shutdown windows.