An experimental study of the resistivity response on fracture process of sandstone with pre-existing flaw

Abstract

Coal rock dynamic hazards are the result of violent energy release from the coal rock body under high stress. It is accompanied by changes in the fracture structure, which can cause changes in the resistivity of the rock mass. Therefore, the resistivity changes of pre-existing flaw red sandstone samples with different angles during load damage were investigated by uniaxial compression experiments. The resistivity change law under diverse fracture types was thoroughly examined, and the influence law of different fractures on resistivity was investigated. The results reveal that the specimen's resistivity responds to stress in an exponential manner, and that the resistivity changes dramatically when the stress reaches the failure stage. The range of λ in the linear elastic stage and plastic stage increases first and then decreases with the increase of the pre-existing flaw angle, but they are all less than 0.2. The proportion of shear crack in red sandstone increases from 50% to 77% with increasing pre-existing flaw angle. When the percentage of both types of cracks is similar, the range of λ during microporosity expansion has a wide distribution, reached 0.34. When the percentage of shear cracks exceeds 60%, the range of λ is less than 0.15. The change of porosity caused by microporosity is the fundamental reason for the resistivity change of specimen. The existence of pre-existing flaw changes the trend of porosity increase and cracks of the specimen during the loading process which leads to different changes of resistivity. This study facilitates the DC method for more accurate monitoring of coal rock dynamic hazards.