Bursting With Flavor

Pipe bursting helps a California contractor replace industrial wastewater pipes without interrupting production.
Bursting With Flavor
The manhole’s cylindrical wall created a void to the left of the M50 ram that was filled with 6-inch timbers and two sandbags to make the resistance wall perpendicular to the pull force.

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Some industrial wastewater lines at a food processing plant in San Jose, Calif., were too small to handle the volume and others were deteriorating with age. Pipe bursting was the only way to rehabilitate them without disrupting the plant’s nonstop operation. The facility’s local mechanical contractor, Therma Corp., subcontracted TRIC Tools of Alameda to do the work.

The first pull would pass under a 4-foot-thick slab supporting multiple 50-foot-tall liquid storage tanks. “No one knew what lay outside that pipe,” says John Rafferty, TRIC’s director of marketing and technical support. “If we hit obstructions, damaged utilities, or the cable or bursting head broke while under the slab, it would be a miner’s nightmare to tunnel to it.” Excavating inside the plant would be equally disastrous and expensive.

Tight safety and cleanliness controls inside and outside the building quadrupled the work.

“Dealing with all the time-consuming extra requirements became the toughest part of the job,” says Rafferty. “Any infractions could result in eviction.” Careful planning and coordination kept the plant operating at full capacity throughout the demanding project.

Windows of opportunity

Therma site supervisor Dave McCall and his team did everything except fuse and pull the HDPE pipe. They also advised TRIC workers on protocol. Each procedure had to be logged and documented by someone on the plant safety team. Any equipment carried into the building had to be disinfected and wrapped in plastic. Workers had to wear hairnets and beardnets even outdoors, and disposable coveralls and boots when entering the plant. “We had to discard them every time we went outside, and we were going back and forth constantly for the second pull,” says Rafferty.

The challenge of the first pull was stabilizing the cribbing against the external wall of a 48-inch concrete manhole. A 100-foot length of 6-inch PVC line ran from a clean-out in the driveway outside the plant to the manhole, passing under the concrete slab on its way. McCall’s crew excavated and shored the launch pit at the clean-out and a 4- by 2- by 8-foot-deep pulling pit behind the manhole.

Semi-tractor trailers use the driveway to deliver ingredients, and they needed an unobstructed approach to the offload site. A truck arrived every four hours and took at least 90 minutes to unload. “Everyone timed their work around the delivery schedule,” says McCall. “That meant moving equipment out of the way and laying plating over the excavations while the vehicles were here.”

Rafferty’s team fused six 20-foot sticks of 8-inch HDPE pipe and the polyethylene end cap the day before the pull, then laid it alongside the perimeter access drive. “The client required a fire extinguisher by the fusing machine,” says Rafferty. “We had to record when we began heating the iron, when we unplugged it, and the 45-minute cool-down before storing it on the premises.”

Tricky timbers

The manhole’s inlet and outlet didn’t align, so the Therma team excavated behind the structure, restricting the pit’s width to 2 feet to avoid encountering adjacent underground supply lines. They cut a hole in the manhole wall opposite the inlet pipe, enabling the cable to pass through the pulling pit, and enlarged the inlet more than 12 inches to enable the bursting head to enter.

“That gave us ample support for the cribbing on the right-hand side of the manhole, and no support on the left-hand side since our inlet path was at an odd angle,” says Rafferty. “The tricky part was making the resistance wall perfectly perpendicular to the pulling force.”

Rafferty used a Sharp Shooter drain spade to cut a crisp 90-degree corner and straight walls in which to situate 6-inch timbers and sand bags to fill the void behind the cribbing and 24-inch resistance plate. “The goal is to set up once, then just push buttons,” he says. The M50 ram, with 48 tons of pulling force, was set vertically in the pit. A trailer-mounted 14 hp/7 gpm/5,000 psi TRIC hydraulic pump powered the ram.

To accommodate the delivery trucks, McCall’s team waited until the last minute to cut a 2-foot-wide slot in the concrete at the entry pit, then sloped the soil toward it. That left the top half of the shoring wall in the way.

“Removing the 10-foot-long segment was an issue because of OSHA standards, but it had to go,” says Rafferty. “Even then, we had to push down on the pipe with the backhoe bucket to assist the angle of entry.” There were no surprises waiting under the slab and the pull was finished in time for the next delivery truck.

Part two

The second pull from the driveway clean-out pit to inside the plant replaced 185 feet of 4-inch cast iron pipe with 6-inch HDPE that tied into the new 8-inch pipe. No gasoline-powered equipment was allowed inside the building.

McCall’s crew drilled and anchored steel poles to the facility’s 6-inch reinforced concrete floor, then pitched Visqueen-walled 20-foot-square by 8-foot-tall tents over all excavations. The tents had 12-inch vacuum fans exhausting into 20-foot-long flex conduit venting through the plant’s ceiling to remove dust.

After workers cut through the floor, they excavated a 14- by 10- by 4-foot deep pulling pit, then dug a reservoir at the head to collect the upstream drainage. They put a sump pump in a 30-gallon plastic tub, running the intake hose to the reservoir and the outlet hose to a bypass drain. Someone always monitored the tub during high-flow periods and occasionally moved the bypass hose to a larger drain to prevent spills.

McCall scheduled an electrician to direct-wire TRIC’s 10 hp, three-phase, 480-volt, 2 gpm/10,000 psi PowerTeam hydraulic pump. “The unit had four thick contact wires and was the size of a washing machine,” says Rafferty. It powered an X30 ram with 29.5 tons of force.

The pulling pit wasn’t cribbed because wood was not allowed in the plant. “Fortunately, the dirt wall was firm enough to hold the resistance plate, yet not too compacted to allow for expansion of the pipe fragments,” says Rafferty. To prepare for the pull, he slid a pre-burster up the 3/4-inch swaged cable and over the shackle (connects the bursting head and cable) to prevent it from doing the bursting work as it entered the small pipe.

As the greasy, dirty cable came out of the pulley during the burst, McCall’s crew wrapped it in white plastic, taped it, and ran it outside along the bursting path to the entry pit. “We were advancing 3 to 4 feet per minute using an average 15 to 20 tons at 3,000 to 4,000 psi,” says Rafferty. “Because of Therma’s efficiency and preparedness, everything went according to schedule and we were done in 25 minutes.”

Triple play

The third pull replaced 200 feet of 6-inch cast iron pipe with 6-inch HDPE. The line had multiple tie-ins of 2- to 3-inch cast iron pipe, requiring three excavations between the entry and pulling pits. “The challenge here was fusing pipe inside a small corner of the warehouse,” says Rafferty. “We couldn’t cross the loading threshold 90 feet away or we’d interfere with the nonstop forklift traffic. The pulling pit for the fourth pull was adjacent to the wall at the other end. Add the fusion machine and we were left with a 40-foot circle for the pipe.”

To direct the pipe into the mechanical fusing jig and align the ends, McCall’s crew drilled and screwed footings in the floor for temporary guideposts. Rafferty followed the same procedures indoors for fusing pipe as he did outdoors.

The host pipe lay in a trench backfilled with gravel. Although the 6-foot-deep pulling pit was shored, the ground behind the 24-inch resistance plate kept caving in. “We had 18 inches of wall missing,” says Rafferty. “If we were to complete the pull, we needed cribbing to stabilize the plate.”

Therma workers dashed across the freeway to their shop and returned with 3-foot timbers wrapped in plastic. However, they weren’t long enough to disperse the pulling force and the wall began compressing again, shifting the ram sideways. Technician Salvador Sainz and municipal sales director Bob Grenier stopped the pull and adjusted the timbers so one edge caught the foot of a shoring strut to extend the area of resistance.

With the cribbing stabilized, the pipe moved at 3 to 4 feet per minute. McCall’s crew had disconnected the tie-in pipes so the bursting head wouldn’t catch and drag them along. Rafferty monitored the intermediate pits, checking on the stretch of the pipe and stopping the pull twice to clear debris collecting in front of the head.

“If 200 feet of pipe stretches even half a percent, that’s a foot,” says Rafferty. “According to the manufacturer, the pipe needs 8 to 12 hours to retract after stretching, but we didn’t have that much time.” To compensate, McCall’s crew began connecting tie-ins at the entry pit, since stretch is minimal to none at the tail end. As soon as they cut the HDPE pipe to make connections in the intermediate pits, they relieved the tension and the pipe popped back.

The final pull, replacing 80 feet of 4-inch cast iron with 4-inch HDPE, ran perpendicular to the 6-inch pipe and tied into the entry pit of the previous job. It was uneventful. “Therma is probably the best primary contractor with whom we work,” says Rafferty. “They made it possible for us to perform our job without a hitch.”


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