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.
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.
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.
This article is submitted by Wolf Krammel for Craftsman Pipe Lining in South Florida. Visit www.craftsmanpipelining.com and get our ebook absolutely free, check out www.craftsmanpipelining.com to learn about the money saving options concerning pipe maintenance, re-lining and to get an e-book "Insiders Secrets" Pipelining absolutely free.