Experimental study on characteristics of surface potential and current induced by stress on coal mine sandstone roof

Abstract

Rocks generate voltage and current when subjected to load. Hence, the study of their characteristics is critical to the prevention and management of mine dynamic disasters and their secondary impacts. To investigate the characteristics of surface potential and current induced by stress on coal mine sandstone roof, an experimental scheme for determining the mechanical–electrical characteristics of rocks is constructed. The aforementioned system tests the evolution rules of current and voltage generated by the coal mine sandstone roof at different loading rates; the formation mechanism and coupling rules with mechanical properties of sandstone are also analysed. Experimental results show that although loading rates may differ, the variations of pressure stimulated current (PSC) and pressure stimulated voltage (PSV) curves are similar. Throughout the loading process, the PSC is divided into three stages: rapid growth, slow growth, and peak; on the other hand, the PSV curve exhibits a ‘double peak’ characteristic. The loading rate changes the current and voltage growth rates and peak values. When combined with mechanical properties, it can be observed that the PSC is related to the effective elastic modulus, whereas the PSV is related to micro-crack and macro-crack events in rocks. The current and voltage generated by the coal mine sandstone roof subjected to load are consistent with stress. The mechanical–electrical properties of sandstone indicate that the change processes in the PSC and PSV result from the coupling effects of various mechanisms. In the compaction stage, these are mainly caused by the piezoelectric effect of sandstone. In the elastic–plastic deformation stage, they are primarily generated by the electric dipoles formed by micro-cracks. In the sandstone fracture deformation stage, the change processes are mainly caused by the crack tip discharge. This study provide an experimental basis and practical results that reflect the microscale process and electrical precursors of sandstone fracturing.