Val Vista Water Transmission Main Rehabilitation—Steel Slip Lining of a 90” PCCP

The Val Vista water transmission main rehabilitation 2014 Project was a construction manager at risk (CMAR) project for the City of Phoenix (City), which included both pre-construction and construction services for the rehabilitation of 6,262 linear feet of existing prestressed concrete cylinder pipe (PCCP). This pipeline delivers approximately 220 million gallons per day of potable water to as much as sixty percent of the City’s population. As the City’s most critical pipeline, maintaining its uninterrupted service is critical. Work on this main could only occur during low demand months from November through April and required extensive coordination with all water production facilities across the City. To gain access to the pipeline, located twenty feet below grade, access portals were created by excavating and installing specialized slide rail shoring. Two existing twenty foot segments of pipe were demolished to allow access to the interior of the pipeline. Once this portal development was established the rehabilitation of the existing 90-inch pipeline could commence. The trenchless technique for slip lining the transmission main is accomplished by installing new steel pipe liners. For this project, 84-inch solid-can and 87-inch split-can liners were installed. Once the liners were installed and welded together, pressure grouting of the annular space between the liner and the existing pipe was completed. After annular space grout was complete, a cement mortar lining (CML) was applied to the new liner pipe. This process essentially creates a new pipe within the host pipe. After the CML was completed, closure pipe segments were installed where the existing segments were originally demolished, and then protected with a structural encasement. The portals were then backfilled using a combination of low strength CLSM, native materials, and select fill. The disinfection, flushing, and startup of the main was then performed. Final surface restorations included asphalt paving, curb & gutter, and landscape replacement, in the affected areas.