Nonlinear Relationship: Rock Hardness vs. DTH Drill Penetration Rate

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DTH drill penetration rate doesn’t drop linearly with harder rock, but follows a complex nonlinear pattern.

 

  1. In soft rock (f=1-3), penetration reaches 60-80cm/min. Rock breaks mainly by shear; impact energy overcomes cohesion.
  2. In medium-hard rock (f=4-6), rate drops sharply to 30-40cm/min. Brittle fracture starts; energy fights both cohesion and friction.
  3. In hard rock (f=8-10), rate stays at 10-15cm/min. Rock mainly deforms elastically; most energy turns to heat loss.

 

For ultra-hard rock (f>12), a “rebound effect” occurs. If impact frequency exceeds rock’s elastic recovery speed, drills rebound. Effective drilling time drops from 85% (soft rock) to under 40%. Reduce frequency below 200 times/min to ease this.DTH drill