不同岩性煤岩电位信号变化规律及机制研究

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

煤岩变形破坏过程中产生的电位信号能够较好表征煤岩损伤演化过程,在煤岩动力灾害监测预警领域具有良好应用前景。目前大多研究主要针对同一类型煤岩失稳破坏的电位特征及规律,对不同类型煤岩失稳破坏的电位特征对比分析缺乏系统研究,同时在微观层次上不同岩性煤岩结构破坏过程及组分对表面电位信号的产生机制影响对比研究较少。为深入研究不同岩性煤岩电位信号响应规律及差异性,选用石墨、原煤、砂岩、花岗岩4种试样进行单轴加载并同步采集其损伤破坏过程中产生的电位信号,分析了4种试样受载破坏的电位信号变化特征。结果表明:石墨试样整体电位信号值相对较低,在裂纹损伤和不稳定裂纹扩展阶段电位信号有较大波动;原煤试样电位信号波动与载荷波动一致,整体电位信号变化相对稳定;砂岩试样电位信号值在压密阶段和弹性变形阶段增大速率较快;花岗岩试样电位信号在裂纹损伤和不稳定裂纹扩展阶段波动较大,电位信号值增大速度加快。通过扫描电子显微镜和X射线荧光光谱仪,从微观结构及组分方面解释了不同岩性煤岩试样电位信号的产生机制。结果表明:在煤岩加载的压密阶段和弹性变形阶段阶段,石墨试样和原煤试样从微观上看有较多的糜棱状划痕,表明摩擦效应是石墨试样和原煤试样的重要带电原因,砂岩试样和花岗岩试样含有较多的O、Si元素,压电效应是砂岩试样和花岗岩试样的关键带电原因,而砂岩试样的电位信号受压电效应的影响更大;在煤岩加载的裂纹萌生和裂纹稳定增长阶段、裂纹损伤和不稳定裂纹扩展阶段、卸载阶段,各煤岩试样电位信号产生原因以试样内部的裂纹扩展和摩擦效应为主,其中裂纹扩展是煤岩电位信号产生的重要原因,裂纹尖端的电荷分离主要包括裂纹尖端应力集中引起的电子逃逸、裂纹扩展引起的裂纹面电荷分离和裂纹尖端放电3个方面。

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.