Rehabilitation of a Large Non-Circular Sewer

Abstract

The County Sanitation Districts of Los Angeles County (CSDLAC) own, operate, and maintain a wastewater treatment and collection system that includes approximately 2100 km (1300 mi) of sanitary sewers ranging from 150 to 3660 mm (6 to 144 in.) in diameter. portion of the CSDLAC's Joint Outfall A Trunk Sewer was constructed as a cast-in-place reinforced concrete conduit having a semi-elliptical cross-section. This paper describes the rehabilitation of approximately 2210 m (7250 ft) of this 2900- and 3200-mm (114- and 126-in.) semi-elliptical sewer using a flexible polyvinyl chloride (PVC) liner embedded in a structural grout. The 2900- and 3200-mm Joint Outfall A Trunk Sewer was constructed in 1927 and included an interior lining of vitrified clay tiles for corrosion protection. The sewer is located immediately upstream of the CSDLAC's Joint Water Pollution Control Plant in the City of Carson, California. Over the years, the majority of the tiles above the low flow level became dislodged and debris accumulated in the sewer to a depth of approximately 2 ft, significantly reducing the capacity of the sewer. Moreover, physical inspections adjacent to manholes indicated the exposed concrete had corroded up to 4 in. The CSDLAC awarded an $8.5 million contract to remove the debris and rehabilitate the sewer in May of 2001. The contract documents specified three acceptable rehabilitation systems to be installed by person-entry methods. The selection of the contractor was based not only on the overall bid price, but also on the contractor's proposal and approach to the project. The selected contractor elected to rehabilitate the sewer with a flexible PVC liner.