Sanitary sewer construction in Las Vegas is a top priority in the fifth-fastest growing mid-size city in the nation. The city grew by 56 percent from 1990 to 1998. This expansion is continuing at a rapid pace so sewer construction in the area is intensifying just as quickly to meet the increasing needs of the population.
The city recently completed the Sandhill Relief Sewer project, which used more than 18,000 feet of centrifugally cast fiberglass reinforced polymer mortar (CCFRPM) pipe from Hobas Pipe USA, Inc. The project required mostly 54-inch and 66-inch pipe, installed primarily by open cut methods. The project also included several elbows, a lateral wye and 30 tee base manholes, most of which have flanged top risers.
More than two-thirds of the pipes are buried in the Las Vegas wash, so design engineer Black & Veatch of Las Vegas specified a slurry pipe zone backfill to prevent flotation in shallow areas and to protect the pipe from erosion.
Pipe specifications called for only reinforced concrete pipe (RCP) with 360-degree PVC T-lock lining and CCFRPM for several reasons. All recent city jobs require only corrosion resistant or corrosion protected pipe to ensure that the pipe's design life is achieved. A low leakage allowance also was specified to minimize infiltration. Finally, some of the pipe would be aligned under streets and burial depths would range up to 25 feet.
Tab Construction of North Las Vegas chose Hobas Pipe since its CCFRPM pipe was priced competitively and its installed cost was projected to be lower than its competitors, even though this was the company's first experience with Hobas. The pipe's long lengths and light weight decreased installation costs.
Tab eliminated the need for anchoring the pipe by developing a low-moisture, lean slurry mix with pea gravel and fly ash ingredients. This flowed well and exerted very little uplift on the pipes, preventing flotation. With the flotation problem solved, the push-together, gasket-sealed joints allowed daily production rates to reach several hundred feet. Tab eliminated the casings specified at four major road crossings by direct jacking about 1,300 feet of the pipe.
The installed pipe has little deflection (ovaling) with none observed above 1 percent. The entire 3.5 miles of line, including the tee base manhole connections, met the leakage requirements and passed the infiltration test with zero leaks. Satisfaction with the pipe's performance resulted in Tab's commitment to order 6,000 feet of 36-in Hobas Pipe for the Clark County Sanitation District. Half of this project will use open cut installation and half will use direct jacking. The Clark County project is Hobas Pipe's ninth contract awarded in the Las Vegas area.
