Insight into rock crack propagation from resistivity and ultrasonic wave variation

Abstract

By using a combined real-time electrical resistivity measurement and ultrasonic wave testing method, the changes in the electrical resistivity and ultrasonic wave information during the crack initiation, propagation and coalescence process of saturated greensand stone under uniaxial loading were investigated, and a method to predict the location of the potential through cracks in the sandstone was proposed based on the anisotropic characteristics of the resistivity. The crack propagation characteristics of sandstone under different loading speeds were analysed from the macro and micro perspectives based on the change in the resistivity. The results showed that there exists a significant correlation between the resistivity change, crack propagation and rock coalescence. Corresponding to the crack initiation, propagation and coalescence processes, the change in resistivity experiences four stages: the stationary stage, descending stage, sudden drop stage and surging stage. The anisotropic change in the resistivity on different testing faces of the rock shows that the anisotropic characteristic contributes to the understanding of the location and orientation where the macro-cracks form in the rock. The increase in the loading rate promotes the local concentration and expansion of micro-cracks in the rock, which can be reflected by the change in the resistivity: the higher the loading rate is, the faster the resistivity descends. With the increase in the loading rate, the failure of the rock tends to be more violent with relatively fewer fractures.