Development and Construction of the Nation's Largest Water Main Rehab Project

Abstract

The Val Vista Water Transmission Main (Val Vista) carries approximately 1/3 - up to 220MG - of the City of Phoenix's (City) potable water from the largest of five water treatment plants within the City's water distribution system. The pipeline consists of a single 15-mile pipeline that includes 72-, 84-, 90-, 96-, and 108-inch Prestressed Concrete Cylinder Pipe (PCCP), installed in the mid 1970's in five separate phases. The pipeline is operated by gravity from the water treatment plant's finished water reservoir, which results in pressures ranging from 10 to 80psi.The pipe was manufactured with many different design parameters, but for the most part it was rated for 150psi with class III wire and 16-gauge steel cans. When the pipeline was originally constructed, much of the easement was undeveloped land though the Cities of Tempe and Mesa. However, through the years the areas surrounding the alignment have grown significantly with high volume roads, retail, residential, and industrial development. With this development, the pipeline has encountered some realignment projects that resulted in the original pipeline being removed and replaced. Once such realignment took place in 1999 at the lower portion of the pipeline on approximately l,000LF of 72-inch pipe. During the removal and replacement project, the pipe was discovered to have significant signs of corrosion. This discovery resulted in the Phoenix Water Services Department to initiate a long term program to investigate the condition of the entire pipeline. This included numerous electromagnetic & visual/sounding inspections, live monitoring, and removal and dissection to determine the level of condition on this critical artery of distribution system. Due to the results of these investigations there were multiple sections of internal carbon fiber installed, and two pilot rehabilitation projects completed between 2003 and 2006. After successfully completing split steel can rehabilitation of 10,000LF of 72-inch on the Val Vista pipeline in 2005 and 2006, the City decided to initiate a program to design the rehabilitation of the remaining 68,000LF so that it could be constructed as funds were available over the next ten years. The design was completed in August 2007 allowing the first phase of construction to be completed in the 2008/2009 shutdown period. Consisting of 18,500LF of 72-, 90-, and 96-inch pipe (Figure 1), this project resulted in the largest split steel can rehabilitation project of PCCP to date in the United States of America.