Potential Problems and their Possible Solutions
The best option for dealing with potential pipe bursting problems is avoiding them or reducing the probability of their occurrence by properly following the recommended design and construction procedures and precautions. Some of the potential problems associated with pipe bursting include sag correction, soil displacement, protecting utilities, bursting system selection problems, unforeseen obstacles, and site restrictions.
If the sewer line has excessive sags, these sags should repaired prior to bursting. However, if they were discovered after bursting, the contractor can reduce the sag by digging at this point and improving the soil support under the pipe. Replacement of a section of pipe may be needed at this excavation. If excavation at this point is not feasible, grouting and stabilizing the soil underneath the pipe may be a solution.
If excessive ground movement is anticipated very close to an existing structure, a ground movements and vibrations monitoring plan should be developed. If dangerous movements are observed, slowing the rate of bursting is mandated. If the movement is still high, bursting should be halted until analysis of the causes and corrective options are studied (including the option of abandoning the pipe bursting method). If there is a gas line, water line, or sewer line that is too close to the bursting head and is at risk of damage, exposing the line reduces this risk significantly. The excavation to expose this utility should be done using means that do not damage the line, such as vacuum or manual excavation. If the pipe is shallow and there is a high risk of damaging the surface pavement, saw cutting the pavement prior to bursting prevents the spreading of the damage to the rest of the pavement. Following the installation, the pavement over the trench can be replaced.
If the bursting is significantly slower than expected, the contractor should determine the reason and consider the available corrective actions. Possible reasons for slow bursting progress, and associated solutions, are discussed below.
The bursting system may not have sufficient power relative to the application (upsize percentage, large diameter, length, etc.). If this problem occurs shortly after the start of the run, the solution is to replace the system with a more powerful one. If the problem occurs close to the pulling shaft, the operation should be continued until the bursting head reaches the pulling shaft. The system is then replaced before the next run if the reason for of the slow progress is not a repair ductile clamp or a fitting. Another option is to consider shortening the length of the runs. If the problem occurs in the middle of the run at a location where excavation is feasible, the bursting head should be exposed and the system replaced. The new shaft can be an insertion shaft for the remainder of the run.
Certain components or accessories of the system (for example, the winch, air compressor, hydraulic components, cutting accessories in front of bursting head, etc.) may be mismatched or undersized. Adding accessories in front of the bursting head to cut PVC fitting, ductile clamps or fittings, etc., as appropriate, reduces the potential of stopping or slowing the bursting operation. Alternatively, upsizing these components (within the allowable range of that system) may be the appropriate solution.
Slow progress may be due to obstacles such as ductile repair fittings, concrete encasement, or change in the existing pipe material along the line. If the obstacle is close to the pulling shaft, bursting should continue slowly until the head reaches the pulling shaft. If the obstacle is far from the pulling shaft, a rescue shaft should be excavated to remove the obstacle, change the bursting head, or add/change cutting accessories.
Flowing or running soil around the pipe can cause excessive friction. Lubrication of the outside surface of the pipe is an effective means to reduce the required pulling force on the PE pipe by reducing the friction between the pipe and the soil. This solution requires a lubrication manifold and lubrication line to be installed before starting the bursting operation, allowing lubrication to be pumped during bursting.
A break in the old pipe in running soil conditions, below the GWT, may result in the pipe filled with dirt so that the intended bursting procedure becomes a piercing operation. The remedy is to verify the bursting head did not damage any nearby water line, and then dewater the site.
In general, it is critical that the contractor ensure that the replacement pipe meets the specification before, during, and after bursting. Adhering to the quality control and quality assurance plans from the manufacturing to shipping to the site, along with proper unloading of the pipe, reduces risk of pipe failure. It is recommended that the pipe fusion process be performed by certified and well trained workers, under appropriate supervision, to reduce the risk of pipe failure at a later time when repair is difficult and costly. For pressure application, the PE pipe should be inspected and pressure tested before the bursting operation as well as after completion of the installation.