Estimation of Compressive Strength of Rocks Using Damping Pressure Pulsation of Hydraulic Rock Drill

Abstract

In a mountain tunnel, predicting geological conditions ahead of the tunnel face is quite important in order to carry out the tunnel construction safely and economically. In the logging survey performed while drilling, which is one of the forward investigations of the tunnel face, drilling data such as percussive pressure, rotational pressure, feed pressure, damping pressure, and speed of the hydraulic drill are measured, and the ground state of the drilling position is predicted. Among them, the damping pressure, which damps the repulsive force from the ground due to the impact of the hydraulic drill, provides information on the geological properties of the hole drilling position. To evaluate geological properties such as compressive strength using drilling data, drilling was performed on specimens that simulated grounds with different compressive strengths, and drilling data was measured. As a result, it was found that pulsation, which is the fluctuation of pressure, was generated at damping pressure owing to the impact of the hydraulic drill. The ratio of the pulsation amplitude to the percussive pressure is a stronger correlation with the compressive strength of simulated specimens than does the specific energy.