The first step of Horizontal Directional Drilling (HDD) is the pilot bore. The hollow drill rods are pushed hydraulically through the ground. The drill head cuts a bore hole into the ground. Drilling fluid (Bentonite) is pumped through jet nozzles in the drill head to loosen the ground. The drill head has an asymmetric steering plate. As long as the drill head is rotated continuously, it cuts a straight bore hole. A sonde inside of the drill head transmits signals to the top and allows continuous locating of the drill head. To change direction, the rotation of the drill head is stopped in a position so that the steering plate points in the required direction. Now the drill head is pushed through the ground without rotation. Thereby it steers into the position (roll angle) of the steering plate.

As soon as the drill head has reached the target pit, it is replaced by a backreamer. This backreamer opens the bore channel and pulls the HDPE pipe in simultaneously. Depending on ground conditions backreamers up to ø 1’000 mm (40”) can be used. This allows to pull in HDPE pipes up to OD 800 mm (32”) or pipe bundles with several HDPE pipe. As drilling fluid Bentonite or Ejactomer are used, mixed with water. The drilling fluid stabilises the bore channel, minimises the friction at the drill rods and at the new HDPE pipe and transports the ground particles through the bore channel into the pit.