Abstract
In the present study, a drilling test using a 66-mm-diamter high-speed (HS) percussion bit was first carried out to investigate the rock drillability of Sori granite, which has a uniaxial compressive strength of about 220 MPa. Durability tests were then performed with Sori granite using two HS bits in order to investigate the effect of the bit weight on the amount of bit wear. Based on the results of the drillability tests, bit weights of about 6 kN and 13 kN were selected. The main results obtained from the durability tests are as follows:
a. The penetration rate of both bits decreased linearly with increasing drilled length. On the other hand, the specific energy increased almost linearly with drilled length.
b. Both bits almost reached the bit-life at the drilled length of about 30 m. A detailed analysis revealed that, for both bits, the torque increased linearly with drilled length, with the final torque at 30 m being about 0.11 and 0.13 kN-m higher than the initial.
c. For both bits, the height-loss of gauge tips was almost identical and increased linearly with drilled length.
e. For both bits, a one-to-one correspondence was found between the increase in torque and the height-loss of gauge tips. This revealed that the torque is a quantitative indicator of bit wear, regardless of the bit weight.
Finally, to investigate the effect of changing the rock strength, a drilling test was conducted using a new HS bit with Shinkomatsu andesite, which has a uniaxial compressive strength of 192 MPa. The one-to-one correspondence mentioned above was observed as well.
