煤冲击破坏的微破裂演化特征及前兆识别

Microfracture evolution characteristics and precursor identification of coal impact failure

煤岩冲击倾向性是冲击地压发生的重要条件。针对冲击倾向性煤微破裂演化特征及前兆识别难题开展研究,利用MTS试验机开展单轴压缩试验,综合运用声发射和高速摄像机监测手段,研究冲击倾向性煤应力变化–弹性能耗散–动态冲击破坏特征,得到煤峰前微破裂事件的时空强发育规律,构建冲击危险度指标,定义冲击危险指数,并开展前兆识别,结果表明:(1)冲击倾向性煤样峰后存在阶梯状子破坏,子破坏的应力降幅值越大,且应力降速率越快,峰后冲击破坏越剧烈,煤样分区微破裂相互交汇造成整体的冲击破坏;(2)煤样内部存在多个破裂成核区域,区域内大尺寸裂纹(大能量事件)是由众多小裂纹(小能量事件)周期性累积集中孕育,峰前大能量事件集中区域与峰后冲击破坏位置基本吻合;(3)在煤塑性应力降附近和峰值应力降前,微破裂事件呈现出短时强烈局部化特征,对应的冲击危险指数均超过1,对煤即将发生的宏观破裂(应力降)具有预警作用,可作为有效前兆指标。研究成果可深入挖掘煤岩破裂前兆信息,为煤岩灾变及冲击地压的监测预警提供参考。

The impact tendency of coal and rock is an important factor of rockburst. Aiming at the microfracture development characteristics and precursor identification problems of impact tendency coal,the uniaxial compression test was carried out by the MTS testing machine. The characteristics of stress change,energy dissipation and dynamic deformation failure of impact tendency coal were studied by means of acoustic emission and high-speed camera. According to the temporal and spatial strong development law of coal micro fracture event in high-stress stage,the impact risk index was defined and applied to precursory identification. The results show that there is stepped sub failure behind the peak of impact prone coal. The greater the stress drop value and the stress drop rate of sub failure,the more intense the post peak impact failure. The microfractures of coal samples intersect with each other,resulting in the overall impact failure. There are many fracture nucleation areas in the coal sample,and the large-scale cracks(large energy events) in the areas are periodically accumulated and bred by many small cracks(small energy events). The concentration area of large energy events before the peak is basically consistent with the impact failure position after the peak. Near the plastic stress drop of coal and before the peak stress drop,the micro fracture events show instantaneous and strong localization characteristics,and the corresponding impact risk index exceeds 1,which can be used as an effective precursor index for the imminent macroscopic fracture(stress drop) of coal. The research results can effectively identify the precursory information of coal and rock fracture,and provide reference for the monitoring and early warning of coal rock disasters and rockburst.