Swiss contractor Tschanz Grabenlos AG, who are based in Luterbach (nearby Solothurn) used their TERRA-JET 3008 ES pit machine to undertake a steep HDD bore in Bibrist. The TERRA-JET 3008 ES can undertake directional bores in lengths up to 150 m (500 ft) and backream diameters up to 420 mm (16.5").
This challenging job involved installing a new HDPE pipe with an outer diameter of 132 mm (5.2") beneath a staircase having a downward inclination of 48 %.
The TERRA-JET 3008 ES pit machine was installed in the entrance pit at the same 48% inclination. The drill path required drilling the pilot bore straight (at 48% inclination) for the first 12 m (40 ft).
Thereafter the drill operator Rolf Kauer drilled in a sharp upward curve at the minimum bending radius of 35 m (115 ft) until the an upward inclination of 10% was achieved. The pilot bore then continued straight at this 10% upward inclination until the drill head reached the target pit. In the target pit the drill head was disassembled and replaced by a backreamer which was connected to the new 132 mm (5.2") HDPE pipe.
During back-reaming the drill operator decided to thicken the bentonite drilling fluid due to the hard ground encountered during the pilot bore. The pilot bore was backreamed up to ø 180 mm (7") and the new HDPE pipe was pulled in for a length of 48 m (160 ft).