The tools and techniques used in the HDD process are an outgrowthof the oil well drilling industry. The components of a horizontaldrilling rig used for pipeline construction are similar to those of anoil well drilling rig with the major exception being that a horizontaldrilling rig is equipped with an inclined ramp as opposed to avertical mast. HDD Pilot hole operations are not unlike thoseinvolved in drilling a directional oil well. Drill pipe and downholetools are generally interchangeable and drilling fluid is usedthroughout the operation to transport drilled spoil, reduce friction,stabilize the hole, etc. Because of these similarities, the process isgenerally referred to as drilling as opposed to boring. Installation ofa pipeline takes place in three stages. The first stage consists ofdirectionally drilling a small diameter pilot hole along a designeddirectional path. The second stage involves enlarging this pilot holeto a diameter suitable for the installation of the pipeline. The thirdstage consists of pulling the pipeline back into the enlarged hole.




