Successful project with the TERRA-JET DJ 40 AT

Challenging rock drilling

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A rock drilling project was carried out in Switzerland using the TERRA-JET DJ 40 AT. The topography and varying soil conditions made this project a particular challenge. The starting point of the bore was located on a hillside, approximately 60 meters above the target area on the lakeshore. From there, the 250-meter-long bore path had to be guided downwards in a controlled manner. At the beginning, the pilot bore passed through soft ground. As it progressed, the drill head encountered a rock formation through which a significant portion of the route had to be drilled. Towards the lakeshore, the soil conditions changed again, and the drill head entered softer material once more. This meant that the drilling process had to adapt to very different geological conditions within a single bore. In particular, the transitions between soft soil and rock required precise coordination of feed, rotation, and drilling fluid.

Pilot drilling with the Rockmaster

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The TERRA-JET DJ 40 AT was used for the horizontal drilling. The DJ 40 AT is equipped with 18 tons of thrust and pullback force and has a torque of 8,000 Nm. This high-performance HDD drilling rig is designed for demanding drilling projects and use in difficult soil and rock formations. In this project, the combination of a long drilling distance, a steep gradient, and changing geology placed high demands on the drilling and tracking technology. The planned route had to be precisely tracked over the entire distance while simultaneously being adapted to the respective underground conditions. For the pilot bore through the rock formation, the TERRA Rockmaster with a PDC bit was used. The 2° bend in the sonde housing made it possible to steer the Rockmaster even in hard ground.

Precise tracking with Mag X Geo

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For tracking the pilot bore, the drilling team relied on the Mag X Geo from Underground Magnetics. Technically, the Mag X GEO operates with 16 frequencies ranging from 0.325 to 41 kHz and is compatible with various echo sondes. Data is displayed on a 7-inch color touchscreen. The system also features integrated data logging and can directly process or synchronize the recorded drilling data for reports. During the drilling process, the tracking system provided essential information about the position and pitch of the drill head. This allowed the actual path of the pilot bore to be continuously compared with the planned route. Especially in a long bore with a significant elevation difference between the start and finish, precise tracking is crucial. Necessary directional corrections can be made early on, and the pilot bore can be guided in a controlled manner toward the intended exit point.

Reaming with high fluid volume

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After the pilot bore successfully exited at the target point, the bore channel was prepared for the new product pipe. This required a back-reaming process. A suitably adjusted drilling fluid supported the removal of the loosened material, reduced friction, and stabilized the bore channel. The DJ 40 AT is equipped with a 510 l/min high-pressure pump from FMC, ensuring sufficient fluid volume for the reamer. This created the necessary conditions for the final installation of the new water pipeline.

250-meter pipe installation

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In the final step, the DN 200 HDPE pipe was pulled into the prepared bore channel. This allowed the new water pipeline to be installed trenchlessly over a distance of 250 meters from the higher starting point down to the lakeshore area. This topography highlights the advantage of HDD technology. Instead of extensive earthworks along the hillside, the pipeline could be laid largely underground with significantly less surface disruption.

Successful operation under demanding conditions

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The construction site in Switzerland impressively demonstrated the strengths of the TERRA-JET DJ 40 AT rock drilling rig. Over a drilling distance of 250 meters, both an elevation difference of approximately 60 meters and highly variable soil conditions had to be overcome. The combination of the TERRA-JET DJ 40 AT, the TERRA Rockmaster for the pilot bore, and the Mag X Geo from Underground Magnetics for tracking formed an optimally coordinated system. In the end, the goal was successfully achieved: a new DN 200 HDPE water pipeline, installed trenchlessly through soft soil and rock down to the lakeshore.

Project data

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Location: Switzerland
Drilling rig: TERRA-JET DJ 40 AT
Drilling length: 250 m
Elevation change: approx. 60 m
Geology: Soft soil and rock formation
Rock drilling system: TERRA Rockmaster
Tracking system: Underground Magnetics Mag X Geo
Product pipe: HDPE DN 200
Medium: Water