PUBLIC WORKS/Las Vegas sliplines to restore aging sewer

Las Vegas has rehabilitated part of its Sloan Lane Interceptor using sliplining to “replace” aging and damaged pipe. The $3.2 million project, which took six months to complete, required minimal excavation and produced little disruption to the community.

Las Vegas built the Sloan Lane Interceptor in 1958 using reinforced concrete pipe (RCP). The sewer line initially served downtown Las Vegas and portions of the city east of downtown, and it was expanded in subsequent years to accommodate the area’s growth.

During a 1996 inspection of the interceptor, workers detected exposed structural rebar affecting 12,500 lineal feet of the pipeline. At the time, most of the line’s RCP was decades old, and years of exposure to sulfuric acid had caused it to deteriorate.

In January 2001, the city hired Bozeman, Mont.-based Barnard Construction to slipline the damaged portion of the line. The contractor dug eight jacking pits at various integrals and removed the top half of the exposed RCP at those points. It then inserted smaller pipe in the line, creating a pipe within a pipe. (The contractor used centrifugally cast fiberglass reinforced polymer mortar pipe manufactured by Houston-based Hobas Pipe.)

By sliplining, the city was able to maintain flow throughout the project’s duration. It also was able to minimize traffic disruption as the new pipe was installed beneath city streets.

“On the Sloan Lane sewer project, [the jacking pits had] nominal dimensions of 25 feet by 12 feet,” says Bert Anzai, principal engineer for the city’s Engineering Planning Division. “The street disruption from these pits was small compared to the [disruption that would have been caused by digging up and replacing the pipe].”

Although capacity was reduced through sliplining, the impact has been negligible, Anzai says. “Prior to the project, the sewer line had peak flows of 18 mgd and a minimum line capacity of 48 mgd,” he explains. “After the project, with the reduced roughness coefficient, the sewer line capacity is 46 mgd. In this case, two mgd of capacity was lost. However, the benefit was a new, structurally sound pipe within an existing structurally unsound pipe.”