A Different Twist on Pneumatic Assist Pulls a California Contractor Through a Tough Pipebursting Job
September 19, 2014
In the East Bay, Phase 5 of the Central Contra Costa Sanitary District’s sewer rehabilitation program for summer 2014 targets thousands of feet of public sewer mains located primarily in the dry oak-dotted hills of Orinda, Calif. The project calls for replacement of 6-, 8-, and 12-in. mains by either open-cut or pipebursting methods. Some pipelines will be upsized and most run through hillside easements between large well-kept properties in this relatively exclusive area.
General contractor Pay Pacific Pipelines Inc., headquartered in Novato, Calif., prepared for the pipebursting portion of the work with large pneumatic hammerheads, actuated by a massive 350-cfm air compressor and guided by a constant-tension cable winch. These hammerheads were at home bursting the larger lines in relatively level areas, and with street access at either end of the burst. Bay Pacific foreman Juan Noriega encountered challenges, however, when the sewers to be replaced were in steep easements in irregular native terrain.
Bay Pacific Pipelines had enlisted L.R. Paulsell Consulting of Crockett, Calif., to video-inspect the sewers in the CCCSD Phase 5 program. Owner Robin Paulsell also uses a TRIC M50 pipebursting system for easement and lateral work, which he leased to Noriega’s crew for this particular job in Orinda. Noriega situated the M50 up on the hill behind the manhole base. The manhole cylinder stack had been removed, and the M50 pulling unit was stabilized by an I-Beam driven into the ground by a small excavator, along with other heavy timbers placed against the manhole base. Noriega first tried pulling upgrade with a standard 8-in. static (non-pneumatic) bursting head. Although it remained in the host pipe path, the standard head came to a halt after only 10 lf of bursting, with a full 50 tons of tension on the pulling cable. The traditionally hard ground of Orinda was even less forgiving in this drought year.
Because Paulsell was out of town on another project, he contacted TRIC to monitor the use of the Unified Force head with his M50 system. TRIC co-founder and president Ward Carter was available for consultation. When Carter arrived onsite, the 200 ft of 8-in. SDR17 HDPE replacement pipe was fused and lying along the lake shore beside the road. The UF head was attached to the pipe and pulling cable and was poised at the launch point, where the sewer crossed under the road and then made a steep ascent up the opposite embankment. The road crossing had been excavated and covered by road plates to preempt the likelihood of the asphalt heaving upwards due to the upsizing of a relatively shallow main, and also because there was a 4-in. gas main crossing over the sewer at the base of the embankment.
The TRIC M50 with the Unified Force pneumatic-assist bursting head proved to be the winning combination. Carter instructed Noriega and his crew to pull at about 25 tons of tension on average — half the pulling capacity of the M50 — and let the rapid-fire hammer “catch up” to the load, so that the pull stayed in the 20 to 30 ton range while moving briskly and staying on track within the 6-in. diameter pipe path. Noriega’s crew performed the 8-in. upsize in hard, dry soil at an average rate of about 5 ft per minute, so that the total bursting time for the 200-ft pull was well under an hour.
John Rafferty is the director of marketing at TRIC Tools Inc., Alameda, Calif.