A Different Twist on Pneumatic Assist Pulls a California Contractor Through a Tough Pipebursting Job

TRIC 8-in. Unified Force bursting head assembly at launch pit.Utility districts throughout the San Francisco Bay area are overhauling municipal sewer lines in an effort to curtail sanitary sewer overflows (SSOs) to the region’s extensive bay and estuary system.

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’s Juan Noriega and field tech fill the pneumatic oiler.One episode in particular involved a 6-in. vitrified clay sewer pipe (VCP) that ran 200 ft from a manhole on a wooded hillside down to the roadway bordering a small reservoir below. The job called for upsizing the existing 6-in. clay pipe to 8-in. SDR17 HDPE plastic. Noriega could not use his pneumatic pipebursting system in this scenario for a number of reasons. His hammer unit was too long to negotiate entry at either end of the intended burst. Also, his constant-tension winch could not be situated on the hill, which eliminated the option to pull upgrade. Previous pneumatic bursts had gone awry when the long, heavy hammer unit blasted out of pipelines that took sweeping downturns, or vertical deflections, descending the hillside. Pipelines with vertical deflection were common in this easement area. If the big hammers went off-course through the top of the host pipe, they erupted right out of the ground because the cable winch could not alter the trajectory of the long, heavy missiles intended primarily for straight runs. If they went astray through the bottom or laterally, they got stuck.

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.

Bay Pacific Pipelines foreman Juan NoriegaPaulsell contacted TRIC Tools Inc. of Alameda, Calif., to rent their Unified Force (UF) bursting head to use with the M50. The UF head employs a small hammer unit — a modified 4-in. diameter piercing tool from Footage Tools of Ontario, Canada — along with a much bigger pull than that of the constant-tension winches used with the larger hammerheads. The typical pneumatic pipebursting formula entails longer, heavier, higher-impact hammer units guided by relatively low-tension winches. The TRIC Unified Force formula is just the opposite, pulling a smaller, lighter, faster-acting hammer with far greater cable tension. The smaller hammer releases the stored energy of a much larger cable under load, and the UF head assembly is considerably lighter and more maneuverable than its larger counterparts.

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.

TRIC co-founder Ward Carter The 350-cfm air compressor onsite had to be throttled down at the hose valve outlet, since the UF hammer unit requires only 75 cfm at 100 psi to operate efficiently. Up at the manhole, Carter and Noriega began to take up cable slack with the M50, powered by the TRIC Hi-Flow 14/7 gpm, 5,000-psi hydraulic pump. The UF head and new pipe slid under the road plates and up the embankment, avoiding the gas main as it disappeared into the hillside. The rapid-fire tapping of the small hammer was immediately subdued as it entered the ground.

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.
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