Launch Slideshow

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Water woes

Water woes

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    Photo: Lockwood, Andrews & Newnam

    Contractors with Garver Construction inspect the damage on a 96-inch steel water transmission main.

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    Photo: Lockwood, Andrews & Newnam

    A Lockwood, Andrews & Newnam engineer repairs interior cracking in a 60-inch prestressed concrete cylinder pipe water main in downtown Houston.

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    Photo: Lockwood, Andrews & Newnam

    Crews from Texas Sterling Construction repair a 42-inch prestressed concrete cylinder pipe water line near Houston's Sims Bayou Pump Station.

As part of its role as program manager and engineering consultant to Houston's Surface Water Transmission Program, Lockwood, Andrews & Newnam Inc. (LAN), Houston, has collaborated closely with the city's Design Branch on a series of emergency repairs to large-diameter water pipelines. During three catastrophic failures, they developed a unique contact management solution to meet the demands of such repair projects.

Harish Jajoo, Houston's Design Branch senior assistant director, said the city's role was to respond as quickly as possible to each disaster and incorporate the advice of LAN and other consultants into the solution. “The first failure occurred in July 1998 when a petroleum pipeline contractor made the costly error of puncturing a 96-inch steel water transmission main,” said Jajoo. “The hole was made approximately 3900 feet west of the city's largest surface water facility, the East Water Purification Plant, in an area where the main had been installed at a depth of approximately 30 feet. Further complicating matters, there were no crossover connections to other mains to permit bypassing the damaged area between the plant and the damaged section.

“The city of Houston mobilized more than 40 staff members within two hours and called LAN to join the repair effort,” said Jajoo. “The onsite team rushed to close butterfly valves and isolate the damaged section of the main. However, since the rupture occurred at night, we weren't able to conduct a complete assessment with LAN and the team until sunrise the following morning.”

By sunrise, crews determined the surface-level damage: The north shoulder of the street under which the main was located had been severely damaged by water erosion. Though the main was isolated, unfortunately the rupture was located in the lowest vertical elevation of the pipeline. Even worse, team members later determined the three isolation valves were leaking. As a result, sufficient pressure remained on the line to further wash away the road.

Since the main would have to be out of service for repair, crews had to take immediate action to avoid the collapse of the city's water distribution system and prevent the need for water rationing.

Due to constraints on draining the line, the contractor assisting the effort suggested an inspection using underwater divers. The divers welded an internal steel patch in place, then coated it and other damaged areas of the pipe. The patch held sufficiently to enable the city to place the main back in service less than three days after the puncture and provide a more permanent repair on the outside of the main.

The team completed emergency repairs in 72 hours. The contractor worked around the clock with support from city crews, divers, and LAN personnel. Crews finished restoration of the roadway at a non-emergency pace for $285,000 for immediate repairs, and $372,000 for total repairs.

It became clear after this failure that a new way to manage emergency repair contracts was needed.

DOWNTOWN DISASTER

The second pipeline incident occurred when one of two major water lines supplying Houston's Central Business District and surrounding areas suffered a catastrophic failure in October 2002. The failure occurred in a section of an existing 60-inch embedded cylinder prestressed concrete cylinder pipe (PCCP) that had been constructed in the mid-1970s. In addition to water-line damage, several private residences, commercial properties, and automobiles also sustained heavy damage.

It was clear to the city and LAN that a quick-turnaround solution was necessary. “Due to the high water demands within the area, there would be a significant pressure reduction in the system if the line remained out of service through the summer,” said Jajoo. “Also, this would place a substantial strain on groundwater pump stations that the city was already trying to limit using due to ground subsidence.”