Pipe repair is a part of city maintenance. Over time, existing pipes become too deteriorated to use traditional repair techniques such as sliplining or patching. When broken beyond repair, it is time to consider replacement options.
Pipe bursting techniques are an excellent choice to replace old worn out lines with new ones quickly.
Engineers should compare both pneumatic and static/hydraulic pipe bursting techniques to determine which method is the best choice for their project. (Read Why a Detailed Geotechnical Report Means Success for Your Trenchless Project.)
What is Pipe Bursting?
When a pipe is beyond repair, it is time for a replacement. Traditional underground plumbing replacement requires an open trench to expose the section of broken line, removal and replacement of the piece.
However, an alternative option requires little digging: pipe bursting. (Read An Introduction to Pipe Bursting.)
Pipe bursting is as the name implies, breaking the old line while installing a new one. The new line attaches to a conical bursting head, which is pulled or pushed through the old line breaking it up and displacing the fragments into the surrounding soil.
While pipe bursting is considered a trenchless technique, there may be relatively small entry and exit pits required to insert the bursting tool and new pipeline into the existing one. However, despite the small access point creations, pipe bursting can often be completed in a matter of hours instead of days.
Pipe bursting is more economical and less destructive to the surrounding environment than alternative methods. (Read Understanding Construction Emissions: What’s Causing Greenhouse Gases & How We Can Improve.)
There are two main ways of performing pipe bursting: pneumatic and static/hydraulic.
What is Pneumatic Pipe Bursting?
When considering pipe bursting techniques, the pneumatic method is the most common system used. For about 80% of all pipe bursting projects, workers use a pneumatic hammer driven process. It is most commonly used for sewer line replacements but is not used on cast iron pipes.
Pneumatic pipe bursting is like pile-driving with the unit delivering compressed air strikes at 180-580 blows per minute. The pneumatic cone-shaped head is attached to a guide cable which helps keep the bursting head aligned with the old pipe.
To begin the process, workers dig an entry pit and an exit pit. Most pneumatic pipe bursting projects use an existing manhole or other access point for the receiving hole. The hammer can be attached to the front of the bursting head, for pipes more significant than 12 inches, or behind the bursting head for pipes smaller than 12 inches.
An air pressure supply hose runs through the new pipe to connect to the bursting tool. The winching cable runs through the old line at the exit point and is attached to the bursting head at the entry point. The winching cable and air pressure are set at a constant value and work together to move the new line through the old pipe.
What is Static/Hydraulic Pipe Bursting?
Static/Hydraulic pipe bursting technique occurs in approximately 20% of all pipe bursting projects. While it can be used for sewer replacement, it is also a top choice for workers replacing water and gas lines. (Read How to Tell if a Gas Line Needs Repair.)
Static pipe bursting is the choice for workers replacing cast-iron lines.
With static pipe bursting, the bursting head and new pipe are pulled through the defective pipeline by a hydraulically operated winch. The wench sits surface side by the exit pit where the bursting cone exits for retrieval. Some wenches use a cable attached to the front of the bursting head, while others utilize a rod.
To begin the process, workers dig entry and exit pits. They then push a cable or rod through the existing line from the exit point to the entry. At the entry point, the rod connects to the bursting head attached to the new pipe. Once connected, the hydraulic winch pulls the new line through the old pipe, breaking up the old pipeline and displacing it into the surrounding soil.
Upon arrival at the exit pit, workers remove the bursting head and rod.
Pneumatic and Static Pipe Bursting Comparison
Both pneumatic and static techniques burst the old pipeline and push the fragments into the surrounding soil. The choice to use one over the other may concern soil conditions, or type of pipe workers are replacing. Cast iron sewer lines should be burst using the static/hydraulic method and not with pneumatic equipment.
With pneumatic pipe bursting, workers use an air compressed hammer system, which helps to drive the new pipe through the old one. While workers pull the new plumbing into place with a winching tool, it is also pushed through using a horizontal pile driving motion. The winch attached to the front end of the bursting device is mainly to help guide it through the existing line and keep it from going off course.
Both methods do require an entry and exit pit to feed the new line through the old. Sometimes, both can use an existing access point or manhole instead of constructing an exit pit. More often, pneumatic pipe bursting techniques are more equipped to use existing manholes or other access points due to not having a long rod to insert and then remove.
Static pipe bursting techniques is a pull-through method. There is no mechanism to push the new line into place. While they can use a cable and winch like the pneumatic method, they generally use a rod to keep the tension and guide the bursting head through the line.
With the pneumatic method, the hammering section is attached directly to the bursting head, either in front or behind, giving the head movable parts. In the static mode, the head is pulled, the bursting head is static with non-movable elements.
Both pneumatic and static/hydraulic pipe bursting methods are useful in replacing sections of sewer, water, and gas lines too deteriorated to repair. However, soil conditions and existing pipeline material may make a difference in which method is best.
Knowing the basic techniques each use to accomplish the tasks can make it easier for project planners to determine the best options.