New higher levels of accomplishment saving money, time, and disruption were achieved during the sliplining rehabilitation of J.O. "B" Unit 1C (Phase 4) in County Sanitation District No. 2 of Los Angeles County (LACSD). On this project, nearly 10,000 ft of existing deteriorated 57" and 63" RCP interceptor was relined with 51" and 57" HOBAS fiberglass pipes using innovative installation methods suggested by the contractor, Cook Construction of Downey, CA. Cook's creativity and skilled execution, LACSD's cooperation and willingness to allow worthy new procedures, and the superior performance of HOBAS pipes all contributed to the high achievements. These included sliplining of several tight radius curves, reducing the number of pits from seven to four by pushing long distances and through PI's, and eliminating two structures and a jacking section.

Specific Needs

Like past LACSD rehab projects, this liner also had to be installed without by-pass pumping of sewage flow. Additionally, a pipe stiffness of 46 psi minimum was required for safe annular space grouting collapse resistance. This pipe class had to be achieved with an OD that would enable a low-risk insertion fit and with an ID not more than 6" smaller than the host pipe to assure adequate flow recovery. As typical, the liner had to be resistant to future sulfide attack and have flush, gasket-sealed joints for fast assembly, leak-free performance and a smooth exterior surface. These critical needs again resulted in an exclusive specification for centrifugally cast fiberglass reinforced polyester mortar pipe (HOBAS or equal).

Curves Sliplined

Three curves, each with a 45 ft. radius, were sliplined using about 175 ft. (total) of 2.5 ft. long sections of HOBAS pipes. The push shafts were purposely located so the curved areas were at the ends of the drives. The short pieces were inserted first, followed by 20 ft. pipes for the straight portion of the line. This was successful even on a 3,500 ft. distance with seventeen 2.5 ft. sections at the front. Because the curves actually consist of mitered pipes, a few of the liner's gasketed joints have angular deflections greater than their design capability. However, the joint gaps were sealed in place by fabricating reinforced overlays across the affected joints on the interior. This work was made possible by LACSD temporarily diverting the flow for a few hours overnight. The curve sliplining achievement eliminated the need to open-cut those areas to accomplish the relining.

Huge Savings

One of the curves is located under I-5. Plans called for a parallel jacked installation with two new diversion structures to reconnect the ends to the original line. Because of earlier successes, LACSD allowed Cook (home office in Albuquerque) to slipline the curve under I-5 too. This change saved over $300,000 which was split between the agency and the contractor according to the value engineering procedure.

High Performance

On the fourth push, approximately 1,800 ft. long, a four degree PI 1,000 ft. from the drive pit was sliplined. Mandrel proofing confirmed that 10 ft. sections would pass through this angle point, so the lead 800 ft. inserted consisted of that length section followed by 20 ft. pipes. Despite pushing through curves and PI's, the approximate average friction factor for the entire job was 0.3 with a range of 0.25 to 0.50, which is typical. In fact, the maximum pushing force was only about 100 tons, even for the longest drives. So easy are the pipe assembly and insertion that sustained installation rates of 260 ft./hr. were achieved, even with the live sewage flows present.

Versatility and Success

HOBAS also supplied a 57" to 51" eccentric reducer and 33" pipes to line the 36" manhole risers. A field lamination was made to connect the new risers to the main pipes. Because of HOBAS pipes' versatility and the continued high success of rehabilitation jobs, four additional LACSD sewer projects using HOBAS pipes are currently in various stages of progress. If you too have sewer renovation needs, contact us today.