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Geotechnical Conditions And How They Relate To Pipe Bursting
Pipe bursting is a method of pipe replacement that involves three main forces that must be overcome to accomplish installing a new pipe. A basic understanding of these three forces is required for anyone involved in a pipe bursting project from conception, to design, through final construction. A more detailed level of understanding of the effects of varying ground conditions (geotechnical data) is essential to the success of a project by the senior team members including engineer, owner, contractor and field crews.
The first force, from which pipe bursting derived its name, is the force required to fracture or “burst” an existing pipe. Most types of pipes from two-inches to more than 48-inches can be split or burst and that is accomplished by pulling a hardened steel head through an existing pipe that is configured to focus energy on the pipe wall until it fails from the inside out.
The second and third force will be the focus of this article. The second force is “expansion” which is the force required to expand the existing ground to allow insertion of the new pipe. Typically expansion of the existing hole (existing pipe inner diameter in inches) by 20-25 percent will be required to install the new pipe. Pipe bursting is the only pipeline rehabilitation method that allows the newly installed pipe to have the same or larger ID than the existing pipe.
This force will change dependent on existing ground conditions. Typical geotechnical reports for construction and, more specifically, trenchless construction, will not be of much value to a pipe bursting project unless they are given for the area inside the original trench. Because the pipe bursting process is replacing a pipe that was originally laid in a trench, the required information for properly estimating the force required to expand the soil to the required diameter needs to be supplied from the original trench design. Often times it is not practical to perform standard soil borings in such close proximity to an active pipe like a sewer, water or gas main. However, any borings must provide data that is comparative to those soils found inside the trench.