Since the early 1980s, pipe bursting has grown from a little known pipe rehabilitation technique in North America, into a widely used and, in many cases, preferred pipeline rehabilitation method. Hydraulic and static pipe bursting projects are now quite common. Royalties for the patented process expired in the spring of 2005, opening the door for more contractors and more equipment options.
Static and Pneumatic Pipe Bursting Methods
During pneumatic pipe bursting, the pipe bursting tool is guided through a fracturable host pipe by a constant tension winch. As the tool travels through the pipe, its percussive action effectively breaks apart the old pipe and displaces the fragments into the surrounding soil. Depending on the specific situation, the tool is equipped with an expander that displaces the host pipe fragments and makes room for the new pipe. As the tool makes its way through the host pipe, it simultaneously pulls in the new pipe, which for a pneumatic application is High Density Polyethylene (HDPE) pipe.
Pneumatic pipe bursting operations utilize twin-capstan constant-tension winches. Winch pulling capacity is chosen based on the specific requirements and conditions of each individual job. Because the winches provide constant tension, they are able to guide the tool smoothly through the host pipe making adjustments for various conditions within the line that affect the tool speed. Twin-capstans help protect the cable drum and the cable itself from extreme levels of stress.
Hydraulically operated static bursting systems with bladed rollers are able to burst/split and replace ductile iron and steel pipes. In addition, these systems also have the ability to utilize a wide range of product pipe.
For sanitary sewer applications, bursting often takes place from manhole to manhole. Water main pipe bursting operations are very similar to sewer applications with the exception of manholes. Since there are no manholes in water applications, pits are needed for winching and launching. Strategically positioning these launch and exit pits can reduce the number of excavations on a project.
The winch/exit pit should be long enough to place the winch boom against the pit face with a reinforcing plate if needed. It should also be large enough to facilitate recovery of the pipe bursting tool.
In the static process exit, launch pits are used in the same way they are for pneumatic bursting. First, the hydraulic bursting unit is positioned in the machine/exit pit. Then the bursting rods are pushed through the host pipe and into the launch pit. A flexible guide rod helps the bursting rods navigate through host pipe.
At the launch pit, the flexible guide rod is removed. The bladed rollers, bursting head, expander and new HDPE pipe are then attached. The specially designed bladed rollers actually split the host pipe instead of ripping or tearing it.
The entire configuration is pulled back through the host pipe by the hydraulic bursting unit. The bladed rollers split the existing pipe, while the bursting head and expander displace the fragmented host pipe into the surrounding soil. The new pipe is pulled into place simultaneously.
The Host Pipe
Burstable host pipes include concrete, reinforced concrete, clay, cast iron and asbestos cement. PVC and other plastics, as well as other flexible pipe materials, can be burst or split. In part, different expander tool configurations are chosen based on the material, size and usage of the host pipe, as well as its depth and profile. Point repairs made to the host pipe may also affect bursting potential.
Terrain and Soil Conditions
Most favorable bursting projects involve pipes that were originally installed by trenching or open cut because the fill material surrounding them is usually conducive to pipe bursting. Upsizing depends on the soil conditions as well.
Is the surrounding soil expandable? Beach sand is an example of soil, with certain water conditions, that will not remain in the expanded state long enough for the installation of the new product pipe. A host pipe installed in a rock trench may not have room enough for soil expansion, especially if the new pipe is an upsize. Some backfill material, such as pea gravel, and very wet conditions will affect the success of a project. The knowledge of such conditions before the project is started is vital.
Depth of cover and the possibility of heaving the surface of streets or other hardscape/landscape is also an issue that needs to be carefully considered. The project designer must take into consideration the actual host pipe size, as well as the size of the expander on a pneumatic pipe bursting application when evaluating and determining the depth requirements of a specific pipe bursting project. With pneumatic bursting, for example, an expander on the tool used to create the annular space needed to install a new, larger product pipe is typically larger than the new pipe itself. That needs to be recognized when calculating depth of cover. So, in order to calculate for minimum depth cover, contractors can use the formula of 10 times the total upsize. This depth will prevent any heaving of the ground and pavement caused by soil displacement
Pipeline History and Closed Circuit TV
It is very important to obtain as much history about the pipeline as possible. The utility should reveal all leakage and repair information including: the type of repair products used and how many; any repairs with ductile iron pipe; and use of steel dresser type couplings, etc.
It is absolutely imperative that closed circuit television (CCTV) inspection of the pipe takes place prior to bursting. If the CCTV work is not done, the bursting work is bound to provide many surprises resulting in excavations and lost production time. Usually, CCTV will not be available prior to the line being taken out of service. CCTV will answer most of the following questions: Are there elbows, tees, offsets, hydrants, air relief valves, gate or butterfly valves in the existing pipeline? How many water services are there and where are they located? And, are there short lengths of pipe visible?
While there is a high level of familiarity with HDPE pipe in pipe bursting, there is still considerable interest in other pipe material options by owners, engineers and contractors.†Various pipe manufacturers are working diligently with pipe bursting†equipment developers and manufacturers to find real world ways to adapt their pipe products to pipe bursting installations.†Through much research, suitable ways to install sectional, gasketed pipe in the static pipe bursting process have proven very successful. Both restrained joint and non-restrained joint sectional pipe have been able to be adapted to the static bursting process, giving contractors and municipalities a much broader spectrum of pipe to choose from for their particular projects.
Collins Orton is a Pipe Bursting Specialist for TT Technologies Inc.