煤柱型冲击地压微震信号分布特征及前兆信息判别

 利用微震监测系统，采集平煤十一矿3次煤柱型冲击地压发生前后的微震信号，分析3次冲击地压期间微震信号的时序特征，并利用FFT方法、分形几何原理研究微震信号的频谱特征和分布变化规律。得到如下结论：(1) 煤柱形冲击地压发生前均有一段明显的微震活跃期，表明围岩系统正与外界交换能量，围岩结构处于非稳态的调整期，冲击地压为当次调整期中能量最大的震动，冲击地压发生后，微震活动程度明显下降，出现震后平静期。(2) 冲击地压的主震信号20 Hz以下低频成分占比例较多，波形图中尾波明显且持续时间长，震动能量级别较大。(3) 冲击地压前震主要频谱成分集中在40～100 Hz，前震发生时间距离主震越近，低频成分越多。(4) 微震事件分维值在大的震动(矿震或冲击地压)发生前会持续下降，在大震临近时会降到某个临界值以下。上述规律对确定预测冲击地压的预警指标以及对提高冲击危险程度判别的准确性具有重要意义。

DISTRIBUTION OF MICROSEISMIC SIGNAL AND DISCRIMINATION OF PORTENTOUS INFORMATION OF PILLAR TYPE ROCKBURST

Using seismic monitoring system,abundant microseismic signals are collected during the period of three pillar type rockburst occurs in No.11 mine of Pingmei group.The time sequence of microseismic signal in this period is obtained and the frequency spectrum and spatial distribution are analyzed by fast Fourier transformation(FFT) algorithm and fractal theory.The achieved results are as follows.(1) An obviously active phase occurred before the pillar-type rockburst happens.It is indicates that the surrounding rock mass system is in an energy releasing process and is unsteady because it is in adjustment phase.The occurring of rockburst is the greatest energy shock in this phase;and after the rockburst,the activity of microseism descends obviously which means that the calm phase after shock is starting.(2) The amplitude of the principal seism in rockburst is greater and it has distinct and extended trailing wave.In the frequency spectrum of principal seism,frequency below 20 Hz takes up considerable ratio.(3) Frequencies of the foreshocks mainly concentrate upon 40–100 Hz.The foreshock contains more low frequency components when it happens closer to the principal seism.(4) The fractal dimension values of microseismic events would decrease continuously before the big seism happens and they totally decrease to a critical value when the big seism approaches.The above achievements will be valuable for confirming warning index for rockburst prediction and enhancing discriminating the danger level of dynamic disaster.