Rehabilitation of a 72-Inch PCCP Transmission Main in Phoenix, AZ

In 2003, the City of Phoenix initiated a program to investigate and identify the condition of their large diameter water mains. With over 150 miles of large diameter pipeline, the City's initial investigation began with the high profile Val Vista Water Transmission Main. This 30-year-old pipeline supplies one-third of all water delivered to the City of Phoenix. The 15-mile long, prestressed concrete cylinder pipeline is jointly owned by Cities of Phoenix and Mesa. The pipeline ranges in diameter from 72 to 108 inches with no redundancy. The pipeline alignment once traversed largely undeveloped land. However, growth in the Phoenix Metro area in the past 30 years has brought residential and commercial development immediately adjacent to, and sometimes above, the alignment. A failure of this pipeline would be catastrophic. Three years of investigation have been conducted to date using both destructive and non-destructive testing. State-of-the-art investigations conducted to provide a complete understanding of the pipeline condition included, 1) Electromagnetic surveys to identify broken prestressing wires 2) Sounding and visual inspection to reveal damaged pipeline segments 3) Metallurgical analyses of the prestressing wire 4) Petrographic sampling to identify carbonation of the concrete coating, and 5) Extensive soils analysis along the alignment. The results of the investigation have identified several pipe sections with wire breaks and delamination of the concrete mortar. To date, 26 pipe sections have been identified that were in need of immediate repair. These pipe sections were repaired using internally-applied carbon fiber to withstand internal operating pressures and external loads. This paper focuses on the long-term rehabilitation of the Val Vista Water Transmission Main. The City of Phoenix initiated a multi-year rehabilitation program to slipline all but one mile of the pipeline using steel pipe. The program begins with sliplining 6,300-foot of 72-inch diameter pipeline in Fall 2005. Sliplining the remaining portion of the pipeline is planned for completion over the next five years. Design, system shut-down and start-up, scheduling, and construction techniques for the Fall 2005 program are discussed.