Laboratory evaluation of laser vibrometer for non-contact rock damage assessment

Abstract

The deterioration of ground such as rock delamination and fracturing can cause considerable safety concerns and result in significant interruption to production. There is a change in seismic resonant frequency when the strata are prone to collapse. A repeated seismic survey is an efficient way to diagnose the deterioration process and predict impending hazards. In this paper, a laser vibrometer method is proposed to sense rock condition in areas where normal seismic sensors cannot be deployed. A laboratory experiment using a laser vibrometer PDV-100 along with eleven geophones was carried out on a block of rock sample. The results have shown that the seismic waveforms obtained by non-contact laser vibrametry and the geophones are very consistent. Significant changes in seismic characteristics are evident when sensing across a rock surface with solid and hole sections behind it. It is also found that significant changes occur to the seismic signals when the holes of the rock sample are filled with different materials. The experiment has demonstrated great potential for laser vibrometer in sensing rock weakening process associated with vibration frequencies which is not resolvable using geophones.