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Pipe Bursting – A Last resort To Pipe Lining


Sometimes a pipe is in such bad condition that modern sewer pipe lining is not possible. Examples would be when extensive sections of the pipe are partially collapsed which is common for Orangeburg pipe, or large sections of pipe are missing which is common for cast iron pipe, or a customer is unfamiliar with pipe re-lining, which is the more modern method used in trenchless pipe rehabilitation. In such cases pipe bursting technology is used.

The pipe bursting technology involves pulling a cone-shaped “head”, with a new high density polyethylene (HDPE) pipe attached, through an existing pipeline. As the head moves through, it breaks the old pipe and pushes the pieces back into the surrounding soil. The head also expands the bore diameter slightly larger than the outside diameter of the new pipe it is pulling in. This reduces friction, but it also makes it possible to replace an existing pipeline with one of a larger diameter. Of course very powerful winches and strong cables have to be used for this type of sewer pipe rehabilitation.

A bursting head with no other attachment is called a static head, and it depends entirely upon the power of a winch to pull it through an existing pipeline. In some cases, a bursting head is equipped with a cutting blade or an internal pneumatic hammer. The cutting blade concentrates all the pulling force into one area, making the initial opening of the pipe easier. In hard, dry soils, or when heavy pipe fittings are encountered, the driving force of a hammer aids penetration.

As the HDPE pipe is pulled into the old sewer pipe that requires replacement, new sections of HDPE pipe are fused together using a plastic welding technology. This makes a seamless pipe that will prevent root intrusion, water infiltration and exfiltration.

There are some limitations to using the pipe bursting process:

  • The first is the line has to be in good enough condition for the cable to be pulled through the line.
  • Pipe Bursting will not fix a sag, or, belly. The bursting head and new pipe follows the path of the old pipe.
  • Rocks, ledge and some other conditions may jam the bursting head preventing it from passing and still require excavation to complete the job.
  • Some bend configurations may not allow pipe bursting as the bursting head may exit the pipe and get stuck requiring excavation.

HIGHLIGHTS OF PIPE BURSTING PROJECTS:

The Villages Hospital in Leesburg, FL:

An unusual event occurred at this hospital one day when they discharge boiling water down a drain waste line that was only designed to convey cool water. The resulting heat softened the pipe which subsequently collapsed along 400’ of its length:

Pipe relining was not an option as this type of trenchless pipe rehabilitation requires the host pipe to be repaired to be in a round or oval form. In this case, some parts of the collapse were so bad the winch cable could not be strung through that area, which had to be excavated and replaced before pipe bursting could begin. But once the process began, the old pipe was pushed aside and the new pipe took its place:

The City of Sarasota Lateral Replacement Test Program:

“Since the beginning, we have proceeded methodically, proving one step before we took the next. Then, we didn’t know how much infiltration was coming into our system through the service laterals. And until we discovered the pipe bursting process, we didn’t know service laterals could be replaced cost-effectively.”

Bill Hallisey,

PublicWorks Director

City of Sarasota, Fla.

The City of Sarasota had been experiencing increased flow at their sewage treatment plants that correlated strongly with the advent of rain. So when it rained, somehow there was water infiltration into their sewage pipes that had already been relined!

Upon further study they discovered that the infiltration was most likely coming from residential sewer laterals that had not yet been relined. The city found that 52 percent of the private sewer laterals were cast iron, 6 percent were Orangeburg, 19 percent were vitrified clay pipes (VCP), and 23 percent were polyvinyl chloride (PVC).

All of the Orangeburg and most of the cast iron pipes were badly tuberculated, so their flow capacity was restricted. All lining technologies reduced the capacity of the laterals even more, and some were prohibitively expensive for the application. However, pipe bursting overcame both those concerns, and actual bids revealed that the pipe bursting technology was affordable using lightweight, modular equipment and small crews to replace the existing sewer laterals. The location of each drain line had already been established in an earlier phase of the program.

Since Sarasota is a coastal community with populated barrier islands, so it has a very high water table which is a challenging environment for pipe bursting as some excavation is required for access points. As a result, well points are necessary at some locations. When used, the well points are established the day before the lateral is replaced and are allowed to run until installation and backfilling are complete.

The City of Sarasota uses white HPDE pipe for its lateral replacement pilot project, providing excellent visibility during video inspections.

Each installation starts with excavation of a small pit (about two feet by three feet) at the property line and another where the service line enters the house.

Vacuum excavation is used to open the pits because many utilities are clustered near the property lines. The soil is cut with a water jet, then vacuumed out by a Vactor truck with a 6-inch tube. Usually, the pits can be excavated in less than an hour.

City code in Sarasota requires that a cleanout be installed every 75 feet in new service laterals. For laterals over 75 feet long, pits are sometimes dug for the extra cleanouts, and the new pipe is pulled from one pit to the next. At other times, the entire length of the new line is pulled first and the cleanouts are installed later. We used small, modular equipment manufactured by Tric Tools, Inc. (www.trictrenchless.com) to install the new lateral lines. Normally, the pulling equipment is set up in the pit at the property line because it is deeper, and therefore offers more head wall surface to pull against. The Tric hydraulic puller can produce a pulling force of 60,000 pounds.

The white, 4-inch SDR 17 HDPE (high density polyethylene) pipe is supplied on 800-foot reels. The color enhances video inspections, and the length greatly reduces the need for onsite pipe fusion.

The replacement pipe for Sarasota’s pilot project is supplied on 800-foot reels. This greatly reduces the need for

onsite pipe fusion.

When the pits are ready, a cable is strung through the existing service line from the property line to the house. There, the cable is attached to a 4-inch bursting head, which has a special blade to help crack or cut the old pipe. In turn, the bursting head is fused to the new pipe. In the pulling pit, the cable runs through a resistance plate and metal frame before it attaches to the hydraulic puller. A diesel-powered Vermeer high pressure pump supplies hydraulic power to the puller. Once the pull begins, the new HDPE pipe is pulled into place at 5 to 10 feet per minute, depending upon the power of the hydraulic pump.

The small hydraulic puller used in Sarasota’s pipe bursting project generates up to 60,000 pounds of pulling force.

When the new lateral line is in place, a double-sweep tee and cleanout is installed at each end, and in any intervening cleanout pits. The tees are then reconnected to the original line at the house and at the property line.

During lateral replacement, cleanouts are installed every 75 feet to comply with city codes.

Restoration work is usually limited to backfilling the pits with dry soil and replacing the original sod or mulch at the surface. Any specialized work such as replacement of brick or tile is usually subcontracted to specialists. The pipe bursting process allows new pipe to be installed under existing driveways, mature landscaping, and even add-on buildings without destructive excavation.

High wet-weather flows Sarasota’s system experiences substantial peak flows during wet weather.

Average dry-weather flows are 7.5 million gallons per day (mgd), but monthly averages of 13.2 mgd and daily spikes as high as 22 mgd have been recorded at the 25 mgd wastewater treatment plant. Dan Castorani, Wastewater Program Manager for the city, explains that before the project began, some lift stations in the project area would surcharge any time the water table rose to less than 2.5 feet below grade. “We believe that’s the level at which large volumes of groundwater start to enter our system through customer service lines,” says Dan.

If, as a result of replacing all the leaking customer service lines in the project area, wet weather flows are greatly reduced, many benefits to the city will follow:

• Reduced system operating and maintenance costs.

• Improved environment from reduced or eliminated sanitary sewer overflows (SSO).

• Elimination of SSO-related fines from regulatory agencies.

• Extra capacity for transportation and treatment of wastewater, allowing more development without expansion of treatment facilities.

“If we prove that customer service lines are the source of most of our wet weather I&I, we can take the next step,” says Bill Hallisey, Public Works Director for the city. At that point, the city may decide to replace more customer service laterals at public expense, or require customers to pay for the replacement.

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