When TERRA developed its first HDD pit launched machine ‘TERRA MINI-JET’, it was quit special for the customers to see and understand this new way of drilling. The advantages of drilling out of a pit save time and money. Often it is simply not possible to drill with a big drill rig because there is narrow space or an area in the mountain region where no flat field is available. That’s exactly when the pit launched directional drills show their strengths.

Comparing to the drill rigs, the pit launched machines are shorter and need less space for installation. The mixing and pumping station as well as the power pack stay out of the pit to reduce the pit length. For the TERRA-JET TJ 3008 ES a pit with only 2.7 m of length is required. For the pit launched boring machines TERRA MINI-JET the pit length can even be reduced to 1.3 m.

With the pit launched machine of TERRA you start drilling at the height of the final pipe. This means you don’t have an entry angle at the beginning and you can start drilling horizontally. With normal HDD drill rigs you first have to drill down to a certain depth until you reach the bore channel of your final pipe. Normally this means you have to drill 5 to 10 m more than necessary. No contractor pays for these first meters. With pit launched machines the operator doesn’t have this problem and saves time and money.

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 420 mm (16.5”) can be used. This allows to pull in HDPE pipes up to OD 355mm (14”) 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.