Phase 2: Expansion Drilling
- The pilot string and the steel pipe are connected to each other using an expansion stage (active or passive).
- The press pipe is hydraulically pre-pressed, while at the same time the Soil being pushed into the press pipe is drilled out by the augers.
- The pilot string guides the steel pipe in the precisely specified direction.
- During the reaming process, the pilot string advances into the target pit, where it is unscrewed and dismantled.
In loose to moderately dense sand and gravel soils, a passive reaming stage is used. In this case, the drill head runs set back within the protection of the steel pipe. In dense soil conditions, it is no longer possible to press the ribs of the passive reaming stage into the soil. An active expansion stage is therefore used, in which a cutting disc runs immediately in front of the steel pipe. The openings in the cutting disc can be reduced depending on the expected rock diameter, thereby minimizing the risk of ground collapse. When tunneling in groundwater, so-called “groundwater locks” are used.