Attenuation of Rod Stress in Percussive Long-Hole Drilling

In this study, a series of percussive long-hole drilling tests using Inada granite was carried out to examine the effect of hole length on drilling performace. Special care was taken to clarify the attenuation of elastic wave at a sleeve coupling which connects the two rods. The main results are summarized as follows;1) The experimental results show that penetration rate decreases and rod stress attenuates with increase of hole length or number of sleeve couplings to pass through.2) Numerical simulation using the spring model proposed by Okubo et al. indicates that calculated results of elastic-wave amplitude and length agree well with experimental results.3) Penetration rate was found to be proportional to transmitted energy into the rock. Specific energy in the percussive drilling test is considerably lower than that in the static penetration test.