Fast-Track Repair of 42-Inch PCCP Water Main Houston, Texas

摘要

During the early morning hours of June 8, 2004, a prestressed concrete cylinder pipe (PCCP) installed in 1991 through 1992 suffered a catastrophic failure. This failure occurred in a pipe section of existing 42-inch (1,067 mm) water line, which supplies potable surface water to Sims Bayou Pump Station in Houston, Texas. Several residential properties were flooded as a result of the failure. The City of Houston (City) authorized Lockwood, Andrews & Newnam, Inc. (LAN), to assist in the failure assessment and to design the repair for the water line. LAN performed a visual inspection of the water line interior around the failure location, and performed testing on wire and mortar samples. Initial test results and observations of the failed pipe section revealed that severe cracking existed in both mortar lining and coating, the prestressing wire did not exhibit signs of hydrogen embrittlement; however, the wire did exhibit severe corrosion, which may have facilitated the onset of failure. Further inspection revealed that the internal cracking appeared consistently at invert, crown and both springlines for a distance of approximately 26,000 linear feet from the pump station. Due to the risk of collateral damage should a second failure occur, LAN and the City determined that the line would not be placed back in service without extensive rehabilitation. Because this line is the only source of surface water to the area, groundwater wells were brought online. These wells were required to operate at full capacity in order to supply the demand during the outage of the line, and hydraulic modeling indicated that the groundwater wells alone were not sufficient to meet the summer peak water demands in the area. Therefore, LAN and the City were faced with the task of rehabilitating 26,000 linear feet of 42-inch water line and safely returning it to service before Summer 2005. This paper presents the options, cost estimates and schedules evaluated to fast-track the rehabilitation. The evaluation led to the conclusion that the most feasible solution was to perform design to slipline the existing line and provide bid-ready documents within two-months, allowing approximately six months to construct the improvements to the 5 mile stretch of water line. The paper will also discuss some of the lessons learned as the project went to construction.