Analysis of resistivity response of stratified briquette during uniaxial compression

Resistivity is a key physical parameter in geophysical exploration, and the characteristics of resistivity variation during coal failure of different structures are different. Real-time resistance test system for coal samples under compression was established. Uniaxial compression experiments were carried out on two – layered briquette samples with different thickness and strength. According to the mechanical strength and resistivity variation during the failure process, the resistivity response characteristics of different structural briquette under the influence of layered interface were studied. The results show that the resistivity of briquette under load failure presents a phased change, and the unstratified sample has a u-shaped change after compaction, and the lowest point coincides with the yield point of the stress-strain curve of the sample. In the process of failure, the resistivity of the stratified samples with different thickness first increased and then decreased. Stratified samples with a larger difference in thickness of the two layers were more severely damaged, and the overall macroscopic resistivity value was larger. In the process of failure, the resistivity curves of stratified samples with different strength first increased and then presented a "U" shape. After failure, the resistivity was 2–4 times that of the initial state. The elastic modulus and compressive strength of the stratified sample are lower than those of the non-stratified sample, and the rate of resistivity change at the peak stress is 1–2, while that of the non-stratified sample is less than 0.5. The closer the thickness and strength of the two layers, the more uniform the peeling part generated by compression. The more apt the regional "series-parallel" phenomenon, the greater the resistivity change rate after failure. The squeezing and breaking of the coal sample body or the interlayer void skeleton will lead to an increase in the resistivity of the coal seam. After failure of the stratified briquette, the surface is exfoliated and the cracks are uniformly connected. According to the failure process of the briquette under load, the mathematical model of resistivity change under the influence of "longitudinal cracks" and "longitudinal + lateral cracks" in the sample is obtained. The cracks in the two layers and through the interface of the two layers make the sample into a "series-parallel" connected circuit, and the overall resistivity of the sample is positively correlated with the crack volume proportion. The description of uniaxial compression law of stratified briquette reflects the electrical anisotropy characteristics in strata geophysical exploration in some coal mines.