Rock Drilling Test with a Rotary Hammer

Abstract

Abstract Various test methods have been proposed for obtaining rock strength; however, further research is needed on estimation methods of hard rock strength in situ. In this study, rock drilling tests were conducted with small handheld rotary hammers in a laboratory with four rocks and in situ at two sites. In spite of the fact that the weight of the rotary hammers and the applied thrust force were relatively low, a few-cm-deep hole could be drilled in about ten seconds even into the very hard rock of which uniaxial compressive strength was more than 500 MPa. During the drilling, rock dust was removed out of the hole through the helical grooves on the drill bit. The increase in temperature had little effect on bit wear, which required no air or water supply into the hole. The uniaxial compressive strengths of the rocks were estimated from the specific energy defined as the energy required to excavate a unit volume in the drilling tests. The drilling with a rotary hammer will be helpful for not only obtaining in situ rock strength in mine developments and underground constructions but also estimating strength of unknown rocks in space exploration.