In all forms of utility construction, damage prevention must be a part of the entire process to ensure a successful and safe process. From planning through execution, the entire project team and all stakeholders must play an active role in preventing damage to buried utilities inside a project area.

Pipe bursting is a well-established method of trenchless pipeline renewal. The process involves pulling a steel bursting head through an existing pipe, which fractures it from within and simultaneously installs a new pipe of the same or larger inner diameter in its place.

Pipe bursting is commonly used to replace buried water, sewer, gas and storm lines, and can reduce traditional excavation of a pipeline project by as much as 90 percent. The benefits from a damage prevention standpoint are obvious, since there is a dramatic reduction in excavation, where most utility strikes and damage occur. However, unlike some methods of trenchless rehabilitation, it does include mechanical excavation.

In order to accomplish a replacement by pipe bursting, there will be a number of strategically located excavations that serve a number of purposes, including insertion of the new pipe, location of the pipe bursting equipment and reconnection of service connections like sewer laterals or water services.

LOCATING UTILITIES

During project planning, it is essential that all utilities are properly located and marked to show location, type of utility, size, pipe material and depth. This will allow the project team to plan for temporary utility relocation or conflicts. Geotechnical reports showing actual conditions inside the existing trench and groundwater levels should be provided when possible prior to the project bid.

Unlike horizontal directional drilling, which installs a new pipe where one does not exist, pipe bursting is replacing a pipe that was previously installed in a trench; therefore, the geotechnical reports should be representative of the backfill and bedding of the pipe to be replaced.

SERVING THREE FUNCTIONS

As the new pipe is installed, a pipe bursting head serves three main functions as it is pulled through the ground. First, it fractures the existing pipe from the inside by applying a radial force created either by a static pull force or a pneumatically driven tool. Second, the existing conduit is expanded approximately 20 percent larger than the new pipe’s outside diameter. Lastly, and simultaneously, the new pipe is pulled in behind the bursting head.

As the head travels through the ground, the earth must either compress or displace to receive the head and new pipe. Depending on the type of soil and the volumetric displacement of the head, forces will be transferred to an area immediately surrounding the pipe.

A part of the construction plan should include the anticipated “potential impact zone” of the pipe burst, and all utilities inside of that zone should be located and exposed or relocated if they become damaged. In many cases, utilities that may conflict with the potential impact zone are “potholed” by use of vacuum excavation, which exposes them and either confirms they are outside of the potential impact zone or allows for the pipe bursting head to pass by safely, at which time the hole is then simply refilled.

In most cases, soil compaction and/or displacement is directed upwards from the crown of the existing pipe. The potential impact zone can be easily calculated and is shown in detailed plans.

EVERYONE’S RESPONSIBILITY

In order to anticipate the potential impact zone, there are three major factors taken into consideration: the inside diameter of the existing pipe to be replaced, the outside diameter of the new pipe that is being installed and the geotechnical conditions found inside the existing trench. By subtracting the inside diameter from the outside diameter and converting to a potential impact zone, a safe and successful pipe burst can be both planned and executed.

It is everyone’s responsibility to promote construction safety and to use best practices when working belowground. Although pipe bursting does not open a trench for the entire length of a utility replacement, it does create forces belowground that require proper damage prevention practices be followed.