L.A. County District Sliplines Sewer Project
The Los Angeles County Sanitation District (LACSD) is conducting a series of sewer renewal projects. The rehabilitation of the North Long Beach Section 1 is a recent example, requiring the lining of more than two miles of deteriorated 30 inch interceptor.
As in many previous LACSD rehab projects, the liner had to be installed without by-pass pumping of the sewage flow. In addition, 46 psi minimum pipe stiffness was required to safely withstand the annular space grouting pressure up to 12 psi.
These specifications had to be met in a pipe with a maximum 28 inch OD to deliver a low-risk insertion fit. However, a minimum ID of 26 inches was necessary to assure adequate flow recovery. The new liner also had to be resistant to sulfide attack and periodic caustic treatments.
Finally, flush, gasket-sealed, bell-spigot joints were needed for quick assembly, leak-free performance and a smooth exterior surface. This combination of criteria led LACSD engineers to specify 26 inch Hobas centrifugally cast fiberglass-reinforce polymer mortar (CCFRPM) pipe.
Three siphons and two significant PIs in this otherwise "straight" section required contractor Mladen Buntich of Sunland to use five access pits to insert the liner pipe which was predominantly in 20 foot lengths. Push loads were low with a maximum of only 20 tons needed, even on the longest drive of 2,450 feet.
Insertion was fast because of the Hobas push-together joints and Buntichs new Akkerman pushing machine. This hydraulic-powered, chain drive unit installed 100 pipe sections (2,000 feet) in only 6.5 hours, a rate of less than four minutes per section. Not a single pipe section was damaged.
Before grouting, the annular space was standpipe tested to the maximum grout pressure with no leaks detected in the liner pipe or joints. Annulus grouting with a 80 pcf cellular foam mix placed in a single lift completed the lining phase of the project. Final video revealed a system that was tight and sound.
With more than two dozen projects completed using over 120,000 feet of CCFRPM liner pipe, LACSD is continuing the interceptor rehabilitation program using more of the same. Following this project, no less than five additional contracts were in various stages of completion using more than 20,000 feet of additional Hobas Pipe.