TRENCHLESS TECHNOLOGY/Sliplining technique averts disruption
When the Los Angeles County Sanitation District (LACSD) discovered that a large section of sewer pipe was severely corroded, it took immediate action. The 1,500-foot section, located along Sepulveda Boulevard in Carson, had a 2-inch layer of hydrogen sulfide inside the pipe.
The location of the damage presented several challenges to LACSD, according to Tommy Sung, director of sewer design for the district. The high-traffic area is surrounded by several businesses, including a grocery store, and freeway on/off ramps. Additionally, the site is near a wastewater treatment plant, and the sewer lines are typically 70 to 90 percent full.
With the high flow level in mind, LACSD realized that it could neither replace the sewer pipe nor bypass the flow without severely affecting the businesses and traffic flow. “To bypass would have affected people even more than replacing the pipe,” Sung says. The district decided to slipline the existing 90- and 108-inch-diameter reinforced concrete pipe with 84- and 96-inch diameter centrifugally cast, fiberglass-reinforced polymer mortar pipe. The liner pipe had to be installed under live flow conditions. That dictated a segmented liner system with gasket-sealed joints so that no workmen would need to enter the pipe. The area surrounding the installation would have to be lined to prevent water damage or overflow.
From a small access pit, crews uncovered the existing pipe to create an insertion point for the slip-liner. The pipe was fitted together externally and installed in a single push with a backhoe. The backhoe was fitted with a lifting beam to control the pipe placement and a push ring to uniformly load the pipe end during insertion.
The pipe was supplied by Hobas Pipe, Houston. KEC Engineering, Corona, Calif., performed the installation. The project cost about $2.9 million and was completed in several weeks.
