Guidelines for installing PE gas pipes using HDD

Horizontal directional drilling (HDD) represents an alternative to the traditional trench cut and cover method, and offers substantial savings for installing polyethylene (PE) pipes in heavily developed urban areas, beneath obstacles such as roads, railways, rivers, etc., and under environmentally sensitive areas where trenching might otherwise be prohibited. This method is ideally suited for soft subsoils such as clay and compacted sand. Subgrade soils consisting of large grain materials (e.g., gravel and cobble), rock, and buried debris make it more difficult to use HDD and may contribute to damage of the pipe and drilling equipment. HDD may represent a cost-effective alternative to pipe splitting and bursting, as well as slip lining, modified slip lining, and soft lining renewal techniques. The installation of a pipe using HDD is typically a two-stage process. First, a small-diameter pilot hole is directionally drilled from an entrance pit to an exit pit along a predetermined path. The thrust and pull-back capabilities of the drilling rig, amount of available drill rod, drill path contour, mud mix and other factors typically limit the distance between pits to about 500 feet. The pilot hole is then enlarged by reaming prior to pulling-in the pipe. This operation usually consistsmore » of backreaming from the exit pit to the entrance pit while at the same time pulling the pipe into the enlarged hole.« less