Moling, the trenchless technique of choice for most contractors when replacing conducting pipe repairs, can be difficult to use in certain ground conditions.
In very soft ground, the weight of the ‘mole’ itself can cause it to sink as it burrows through the ground as there is insufficient support from the ground, or the ground cannot provide enough resistance for the action of the mole to advance forwards.
In very hard rocky ground, the mole can be diverted off course by rocks. On severe inclines, especially over longer distances, moling success depends more heavily on operator skill at starting the mole at the right angle to appear in the receiving pit.
Why does this matter?
Moling is non-directional, which means it cannot be steered. Moling relies on the skill of the operator to line it up correctly to the receiving pit, as once it is in the ground it’s course cannot be altered. If the ground is very soft, there may be insufficient resistance from the ground for the pneumatic ramming effect of the mole to advance forwards. Because of these factors, often open cut excavation is selected for pipe repairs despite the additional time and expense it creates.
If left unchecked?
In the event the mole is knocked off course, then there is a risk of ‘losing the mole’ or spending considerable extra time digging the mole out if it can be located, or ‘backing’ it out of the ground. There is also a risk that the mole may hit another utility pipe, or damage property by moving off its intended course. All of these scenarios add time and cost to any site project.
Solution
Pipe pulling methods use the existing pathway of the old pipe to tow the new pipe in and through. Therefore, the relative hard or softness of a ground condition has less overall impact on pipe pulling approaches. Pipe pulling can be adopted for pipe repairs in very soft ground, rocky ground and on inclines, thereby offering an alternative to open cut excavation when moling is less effective.
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