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Down-the-hole drilling
DTH hammer drilling
In down-the-hole drilling a drill rod is fitted with a hammer at its lower end. The hammer, which is mounted on the drill bit, is activated through the addition of compressed air and driven into the ground – simultaneously rotating and impacting. A flushing current collects the loosened drill cuttings and conveys them upwards. This method is mainly applied for hard to very hard rock and/or for penetrating large boulders.
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Leader top for auxiliary rope
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Rotary drive
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Leader
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Casting tube
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Casing shoe with ring bit
Process principle of cased DTH hammer drilling
1. Setting the DTH hammer with drill rod and casing on the drilling point.
2. Rotary and percussive drilling of the drill string under compressed air supply.
3. After reaching the final depth, unlocking of the drill rod with DTH hammer and pilot bit.
4. Withdrawal of the drill rod, DTH hammer and pilot bit out of the casing.
5. Completed cased borehole.
Video: Down-the-hole drilling
The video shows the down-the-hole drilling method for very hard soil or rock.
Cased down-the-hole drilling
A rotary drilling rig, type LB 20, working with down-the-hole hammer inside a casing.
Discharge of drill cuttings
A flushing current conveys the loosened drill cuttings upwards and exits at the upper end of the casing.
Video: LB 16 unplugged DTH drilling
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