Study on variation law and mechanism of coal potential signal with different lithology

The potential signal generated in the process of coal rock deformation and failure can better characterize the damage evolution process of coal rock, and has a good application prospect in the field of coal rock dynamic disaster monitoring and early warning. At present, most of the researches focus on the potential characteristics and laws of the same type of coal rock failure, and there is a lack of systematic research on the comparative analysis of potential characteristics of different types of coal rocks. At the same time, there are few comparative studies on the effect of different lithology coal rock structure failure process and components on the surface potential signal generation mechanism at the micro level. In order to deeply study the response law and difference of potential signal of coal and rock with different lithology, four kinds of samples, graphite, raw coal, sandstone and granite, are selected for uniaxial loading and the potential signals generated in the process of damage and failure are collected synchronously. The variation characteristics of potential signals of four samples under loading and failure are analyzed. The results show that the potential signal value of graphite sample is relatively low, and the potential signal fluctuates greatly during the crack damage and unstable crack propagation stages. The fluctuation of the potential signal of the raw coal sample is consistent with the fluctuation of the load, and the variation of the overall potential signal is relatively stable. The potential signal value of the sandstone sample increases rapidly in the compaction stage and the elastic deformation stage. The potential signal of the granite sample fluctuates greatly in the crack damage and unstable crack propagation stages, and the potential signal value increases faster. By scanning electron microscope and X-ray fluorescence spectrometer, the generation mechanism of potential signals of coal samples with different lithology is explained from the aspects of microstructure and components. The results show that there are more mylonic scratches from the microscopic point of view in the graphite and raw coal samples in the compaction and elastic deformation stages of coal rock loading, which indicates that the friction effect is the important reason for the electrification of the graphite and raw coal samples. The sandstone and granite samples contain more O and Si elements, and the piezoelectric effect is the key reason for the electrification of the sandstone and granite samples, and the potential signal of the sandstone sample is more affected by the piezoelectric effect. In the crack initiation and stable crack growth stage, crack damage and unstable crack propagation and unloading stage, the potential signal generation of each coal sample is mainly caused by the crack propagation and friction effect inside the sample. Among them, crack propagation is an important reason for the generation of coal-rock potential signals. The charge separation at the crack tip mainly includes three aspects, including electron escape caused by stress concentration at the crack tip, crack surface charge separation caused by crack propagation and crack tip discharge.