Water leaks, as many as five per week, made life hectic for the Public Works crews in Big Spring, Texas. They also consumed too much of the city’s small budget.
Most repairs or replacements of the 50- to 75-year-old cast-iron pipes were open-cut. Contractors used pipe bursting or CIPP lining only when traffic disruption was an issue.
The department’s in-house construction replacement program began in 1993. “Our goal was to replace at least five miles of pipeline per year,” says Todd Darden, Public Works director and assistant city manager. “We’ve seen a reduction in leaks from 325 in 1993 to 165 in 2008.”
That year, the Texas Department of Transportation resurfaced U.S. 87, one of four arteries bisecting the heart of the old downtown district. As part of the restoration-revitalization project, utilities upgraded their services.
“Ten contractors were working on these projects consecutively in conjunction with all the street rehabilitation,” says Darden. “We had construction going in every direction within a four-block area.” The last thing he wanted was to dig up the new road to repair future leaks. Voters approved a bond to replace the water pipes.
To stay ahead of the road-surfacing crews without inconveniencing homeowners for more than one day, Stephen Bennett, a consulting engineer from Parkhill, Smith and Cooper Inc. in Lubbock, proposed pipe bursting with pre-chlorinated pipe. “It’s a new, highly efficient, fast process that we love,” says Darden.
Phase 1, completed in November 2008 replaced 17,550 feet of 2- to 12-inch pipe with size-on-size and some upsized pipe. Phase 2, completed in August 2009, replaced 9,560 feet of 6- to 12-inch pipe. The average pull was 450 feet per day, and the most pipe replaced in one week was 2,600 feet.
Mr. Clean
Shelly Eberhart, owner of SKE Construction in Alvin, Texas, won the pipe-bursting bid. “The lines were so badly tuberculated that my fist wouldn’t fit inside the 8-inch pipes,” she says. Eberhart divided her 12 men into crews to excavate entry and exit pits, dig up services, and chlorinate and fuse 40-foot sticks of HDPE pipe. This crew worked in a yard close to the bursting points.
The men averaged one pull a day, usually 450 feet between valve boxes, enabling the fusing and prechlorination team to stay two days ahead of the bursting schedule. The assembly crew welded three or four pulls together using a McElroy 412 fusing machine, then began the chlorination process per Bennett’s specifications.
“Each burst has a number that we write on the pipe and in a log,” says Eberhart. “The log also records the hydrostatic and chlorination tests.” Tests are run simultaneously on the fused pipe.
After inserting a styrofoam pig in one end of the pipe and pouring 25 mg/l of powdered chlorine behind the swab, the men welded on the bursting head. They injected water and air through the head, and hydrostatic and pneumatic pressures pushed the swab through the pipe.
“Pressurization also lets us check the welds for leaks, while the swab pushes out any remaining materials,” says Eberhart. “Once the swab pops out, we pour in fresh water and take a sample.” The samples are driven daily to an independent laboratory 50 miles away to analyze the water for bacterial contamination.
Meanwhile, the pipes are flanged, capped, and held under 150-psi pressure for 24 hours. The sampling process is then repeated. If the pipes pass the second biological test, they are drained, capped, and dragged with a backhoe or excavator over 2-inch HDPE rollers to the bursting site.
Look who’s coming
Before a scheduled burst, another SKE worker hangs notification flyers on residents’ doors and knocks to let them know that the city will turn off the water at 8 a.m. the next day. “It’s a lot of leg work, but the citizens are happy,” says Eberhart. “We even bring cases of bottled water to the elderly. If businesses or nursing homes must have water, we will bypass it to their building,” says Eberhart. Most people, however, are at work and unaffected.
Many valve boxes were a block apart, or 450 feet. The average depth of the bursts was four to six feet. Eberhart’s team used a self-contained, hydraulic/static Grundoburst 800G 80-ton static pipe-bursting system with Quicklock rods from TT Technologies Inc. Once the machine was in the exit pit, workers shuttled the rods through the old line to the launch pit, hooked the rods to the bursting head, and pulled in the new line.
The bursting blade has vertical and horizontal cutting wheels that split the top and sides of host pipes without ripping or tearing them. “The bladed wheel system requires less power than other static systems and helps prevent potential damage to the product pipe,” says Matt McAfee, project manager. An expander attached behind the cutting blade spread and displaced the split pipe into the soil during the pull.
Once the crew cut off the bursting head, they pigged the line, added water, and took another sample to ensure that the pipe had not become contaminated during installation. When residents returned home from work that day, they found their service restored and their doorways accessible.
“We are certainly happy and excited with the results,” says Darden. “I highly recommend this approach to entities looking to replace their water lines, especially in areas where they want to minimize delays and keep traffic moving for the convenience for the traveling public.”
