Estimation of the stability of rock blocks by analyzing hammering sound

Abstract:

The hammering test has been widely used as an easy method to detect unstable rock blocks which have high risk of peeling off from rock slope. The evaluation of the stability of the rock blocks by the hammering test is based on qualitative expert judgment. In this study, the authors analyzed the sound obtained from the hammering test, and proposed a method to evaluate quantitatively the stability of the rock blocks based on the analysis results. The authors used a hammering apparatus which is able to apply constant hammering force to an object in order to evaluate the stability of the rock blocks based on the intensity of the sound. The authors simultaneously obtained the sound pressure waveform and the vibrating acceleration waveform when hammering rock blocks, and verified the Fourier amplitude spectrum form of them were roughly agreed with each other. This result shows that the sound pressure data obtained by the hammering method contains information on vibration of the rock blocks. In addition, the authors found that the amplitudes of the sound pressure Fourier spectrum from the rock block with open cracks were larger than that from the rock block with closed cracks. Similarly, the amplitudes of the sound pressure Fourier spectrum from the rock block were larger than those from the bed rock without crocks. These differences were remarkable in the frequency range between 0 Hz and 1,000 Hz. Based on these results, the authors suggested a procedure to estimate quantitatively the stability of the rock blocks on slopes by focusing attention on the sound pressure Fourier spectrum from the rock block in frequency range between 0 and 1,000 Hz.