From the magazine, HDD

Horizontal directional drilling with Grundodrill 7 X

The mission for Tracto-Technik was to produce a pipe connection from an 82 m deep well to the swimming pool. As an ideal groundwater vein could not be located close to the pool itself, a deep well was formed in a neighbouring park 110 m away.

The 750 sq m large swimming pool did not have the usual vertical side walls, but instead shore zones, making it possible to enter the water gradually just like at the beach. This was the Grundodrill 7 X’s “maiden voyage” under practical jobsite conditions.

The pilot bore lead through a terrain which was not easy to survey at a depth of approximately 150 m below greens, pavement areas and a row of trees. The bore path was exactly traced with a sonde situated in the bore head tip and ensured that the gas, water and power service lines were undercrossed securely.

After the pilot bore with a size 110 mm steering plate, an intermediate clearance was necessary where the bore head was exchanged for a backreamer with a diameter of 210 mm. By reversing the drill rods, the backreamer expanded the bore profile, so that the two plastic pipes, each with an outer diameter of 75 mm, could be pulled in within only 1.5 hours.

One of the pipes was required for the water supply and the second as a protection pipe for power and control cable of the well pump. The preliminary examinations for the bore had shown that the underground consisted of stony ground, typical of the Sauerland area.

During its first task, the Grundodrill 7 X was able to show how the pulling and thrust forces can team up with the torque and the drilling fluid capacity to form a powerful propulsion. In extreme situations, a percussive hammer can also be switched on to provide a further 28 tonnes of ramming energy, thus speeding up the boring process even more.

In order to transfer these forces safely, a powerful drill rod is required, which is why all Grundodrill types are equipped with a special twin-drive drill rod. Their threading has a conical, special design, which enables the threaded parts to be screwed together more easily.

At the same time, the torque is reduced which is necessary for loosening the drill rods during the reverse mode. The carefully thought out geometry and the high quality steel increase the life performance of a twin-drive drill rod by about 40 per cent compared to a standard drill rod working under the same loads. A supply of drill rods to cover 120 m is available in the exchangeable box on the bore rig. Single rods are lifted out of the box semi-automatically and sensor steered, placed in to the guide and greased during the screwing on process. All thrust functions are regulated step-less via joystick by the operator from the integrated, comfortable operator seat.

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