原煤卸围压过程微震信号响应特征*

为了研究煤体采动卸荷失稳破坏的微震动态响应规律，基于热流固耦合三轴试验机进行含瓦斯原煤卸围压试验采集试验过程中的微震信号，进行连续小波变换及4层小波包变换，识别煤样破裂信号，提出煤样破裂干扰信号的时频特征及相应的微震事件分布与破坏演变的特征。研究结果表明:加载初期甚至整个轴压增加过程中，煤样内部裂隙被压密，无新裂隙产生，基本无微震事件，开始卸围压时煤样破裂数量迅速增加；内部裂纹扩展信号主频为700 Hz，前期煤样内部裂纹扩展缓慢，事件产生频次低；煤样破坏信号主频为800 Hz，其频率跳变异常，信号频率成分无明显分带；煤样破坏时微震信号能量最大，破坏过程中伴随不同部位间相对位移，产生摩擦、揉搓，破坏频率成分复杂；煤样破坏时微震事件频数最大LH-2事件总数为176，破坏时每分钟事件数为76，破坏后事件数为92，分别占总事件比例43%，52%；LH-3破坏事件数及破坏后事件数分别占比36%，62%。

Response characteristics of micro-seismic signals during unloading confining pressure process of raw coal

To study the micro-seismic dynamic response law of coal instability and failure caused by coal excavation and unloading,the unloading confining pressure tests of gas-bearing raw coal were carried out by using the thermal-fluid-solid coupling triaxial test machine.The micro-seismic signals in the test process were collected for continuous wavelet transform and 4-layer wavelet packet transform to identify the signals of coal sample fracture,then the time-frequency characteristics of coal sample fracture interference signal and the corresponding distribution and failure evolution characteristics of micro-seismic events were put forward.The results showed that in the initial stage of loading and even in the whole process of axial pressure increase,the internal fractures of coal samples were compacted,there was no new fracture,and there was basically no micro-seismic events.When the unloading confining pressure started,the number of coal sample cracks increased rapidly.The main frequency of internal fracture propagation signal was 700 Hz,and in the early stage,the internal crack propagation of coal sample was slow,and the frequency of events was low.The dominant frequency of coal sample destruction signal is 800 Hz,its frequency varies greatly,and the signal frequency component has no obvious zoning.The energy of micro-seismic signal at the moment of coal sample failure was the largest.The failure process was accompanied by the relative displacement between different parts,resulting in friction and rubbing,and the failure frequency components were complex.The frequency of micro-seismic events at the moment of coal sample failure was the largest,and the total number of LH-2 events was 176.The number of events per minute at the moment of failure was 76,and the number of events after failure was 92,accounting for 43% and 52% of the total events,respectively.The number of LH-3 failure events and post failure events accounted for 36% and 62%,respectively.