Horizontal directional drilling (HDD) is also referred to as directional boring or trenchless excavation. This process is accomplished by using a surfaced-launched horizontal drilling rig the pushes a steerable beacon into the ground with rods that screw together.
An entrance pit and receiving pit are required, but the bore is all made under the surface greatly reducing refurbishing costs and disruption to roads, railways, water ways, etc. The beacon is contained within a drilling head that has an angled point on it. To drill straight, you spin the rods, to go up, down or left and right, the rods do not spin and are pushed in the clock position that you want the rod to travel. In order to detect the head angle, rotation, direction, and temperature an individual continually walks over top of the head/beacon with an electronic locator and then the data is either manually or wirelessly relayed back to the drill operator thus allowing for accurate horizontal drilling direction and depth.
The process is added by the use of a viscous fluid referred to as drilling fluid or mud. The receiving/entrance pits also allow the recovery of this fluid reducing costs and preventing waste. This fluid is a mixture of water and bentonite or polymer which is pumped thru the rods and head to facilitate the removal of cuttings, stabilize the bore hole, cool the cutting head, and to lubricate the passage of the product pipe. The first stage drills a pilot hole and the second stage involves pulling back a cutting tool called a back reamer. The diameter of the reamer (up to 1200 mm) depends on the size of pipe, conduit(s) or HDPE duct(s) that you want to pull back into the bore hole.
The third stage is where the pipe or duct(s) are then pulled back into the enlarged hole made by the reamer.