As the nation's underground infrastructure ages, pipe bursting has gained momentum as an alternative to more traditional rehabilitation methods. It can be faster, more efficient, cheaper and less disruptive than open cutting. Unlike pipe lining, it offers more than a simple cosmetic fix, providing the opportunity to upsize utilities to provide additional capacity. It can eliminate some of the engineering and permitting needed to get a relocation project off the ground. And, since new pipes are installed where the old pipes existed, the risk of hitting or damaging existing utilities is minimized.
While pipe bursting has been used in the U.S. since the early 1980s, it's only been within about the last decade that it has taken hold and become more popular. As the technology continues to evolve, so do the size and complexity of projects.
"Initially, it was pretty much confined to replacing low-pressure, cast iron gas mains with HDPE pipe," says David Holcomb, vice president/regional manager, TT Technologies. "But now we're seeing it being used to replace potable water and sanitary sewer lines, as well, and in diameters that range from 3/4 to 54 in. (O.D.)."
To determine if pipe bursting is a viable option for a particular project, ask questions about the environmental/social impact, type of host and replacement pipes, soil conditions and depth/length of pipe. The answers will influence a particular job's success rate and will help determine whether or not it can even be done.
What is the impact?
Like horizontal directional drilling, pipe bursting has a minimal impact on the environment when compared to open-cut trenching. You only need to move dirt for entrance and exit pits, and any service connections.
"You don't have to dig up the entire street," says Holcomb. "That means it's usually faster, because there's less excavating and you don't have extra time required for restoration after a new pipe has been installed."
That can lead to time savings in other areas, as well, such as less disruption to traffic, minimized bypass pumping for sewer systems and shortened duration of temporary services that may need to be installed for water. "If you can replace a pipe via bursting, it's typically faster, so those temporary services don't have to be in for long periods," Holcomb states. "Any time there's a time savings, there's also a cost savings, because time is money."
Pipe bursting is a great choice for rehabilitation in highly populated areas, says Matt Collins, product manager, compact utility and pipe bursting, the Ditch Witch organization. "When you look at open cut, you may run into social impacts on the community," he says. "You're looking at tearing up streets - some of which are in areas where you have store owners who make a living by the traffic that goes up and down the street." As such, the social impact costs must be weighed along with the restoration costs for replacing the roads.
While pipe bursting can be faster and less costly, there are still situations where open cut may be preferred. "If there are a lot of laterals or taps, it doesn't make a lot of sense to burst, because you need to expose those laterals. This requires that you dig a pit," says Collins. "In these situations, open cut trenching would be a better choice."
What type of pipe?
The type of both the host and replacement pipe plays a role in whether a static or pneumatic pipe bursting process should be used. Static systems can be used to burst existing fracturable pipe (those that fracture upon impact, such as clay and cast iron) and non-fracturable pipe (those that are stable under impact, such as steel and ductile iron). Pneumatic systems are suitable for fracturable pipe only.
Pneumatic systems use a bursting head that is driven by compressed air. A cable is hooked to the bursting head to guide it and provide constant tension. As the head moves through the host pipe, it fractures it via dynamic energy. Fragments are driven into the surrounding soil, the soil is displaced and a new pipe is pulled in simultaneously.