INFLUENCES OF DRILL BIT WEAR ON DRILLABILITY OF ROTARY PERCUSSION DRILL MACHINE AGAINST ROCK MASS

For NATM tunnel construction method, it is very important problem to clarify the influences of drill bit wear on drilling rate of rotary percussion drill machine against several rock masses. Here, the fundamental relations between amount of wear and drilling time, and drilling rate and amount of wear have been investigated in laboratory test for granite, sandstone, andesite, diabase and quartzite by use of a small hammer drill bit. As an in-site test, the relations have been clarified for the same rock masses by use of several actual rotary percussion drill machines. As the results, the wear life and the critical distance drilled could be estimated by measuring the wear velocity of drill bit and the variations of drilling rate, or by substituting the bit diameter, the thrust, the impact energy, the index of rock mass strength for wear, the coefficient of crack and the radical compressive strength into the given equation.