煤体单轴压缩感应电荷时频演化规律与失稳破坏电荷评价指标

为了有效预测预报煤岩破坏所引起的动力灾害,介绍了受载煤体变形破坏电荷产生机理与感应电荷监测原理,开展了煤体单轴压缩过程感应电荷监测实验,采用基于假设原理的Lilliefors检验方法研究了有效电荷产生的初始时刻,获得了煤体破坏演化过程的应力与感应电荷的时序共性特征;研究了加载前期与破坏后期电荷信号的频域特征,设计了基于FIR方法的低通滤波器,得到了滤波后的有效电荷信号;基于煤体破坏演化过程的电荷时频特征,构建了失稳破坏电荷评价指标;开展了井下有、无动力显现的电荷监测试验,使用研发的本质安全型电荷监测仪验证了监测动力破坏现象的有效性。综上研究结果表明:Lilliefors检验方法能够判识煤体加载初期所产生的有效电荷信号,得到了压密阶段基本为白噪声信号,弹性阶段会产生不易识别的、少量的、且与白噪声混合的低幅值有效电荷信号,弹塑性过渡阶段会产生易于辨识、幅值相对增大且连续性较差的电荷信号,塑性阶段与破坏阶段的有效电荷信号随应力降次数增多而增多,随应力降幅度增大而增大,两阶段的电荷信号波动幅度较为剧烈,高幅值电荷信号连续性较强;通过时频变换,得到电荷信号白噪声主频不小于50 Hz,煤体破裂所产生的电荷信号主频不超过15 Hz,设计的FIR低通滤波器可有效降低噪声信号,能保留高幅值与高波动性的电荷信号;建立的电荷累积量、平均电荷强度、电荷变异系数3种评价指标,它们均能良好地反映出煤体的破裂状态,平均电荷强度还可反映出煤岩体的应力水平,变异系数能更加准确地识别煤体进入加速破坏阶段的前兆点;在采动影响下现场各测点的电荷变异系数与平均电荷强度明显比无采动影响的数值更大,电荷变异系数随着远离工作面而逐渐减小,平均电荷强度在超前工作面支承压力峰值影响范围内达到最大值,说明电荷法能够有效监测巷道的动力破坏情况,可为煤矿动力灾害预警提供一种新的监测手段。

Time-frequency evolution law of charge induced by coal uniaxial compression and evaluation indexes of charge for instability failure

To effectively forecast the dynamic disasters caused by coal and rock failure,the mechanism of charges generation and the monitoring principle of charge induced by loading on coal with deformation and failure are introduced.The monitoring experiment of charge in the course of uniaxial compression coal is carried out.The initial time of effective charge generation is studied by the method based on hypothesis principle.The commonality characteristics of time series relationship with stress and induction charge in the process of evolution of coal failure are obtained.The time frequency characteristics of charge signals in the early stage of loading and the late stage of failure are studied,and a low pass filter based on the FIR method is designed to obtain the effective charge signals.Based on the time frequency characteristics of induction charge in the process of coal failure evolution,the evaluation indexes of charge signals for instability failure are constructed.An intrinsically safe charge monitor is developed.The test of charge monitoring dynamic appearance in the underground is developed.Also the effectiveness of monitoring results is verified.In conclusion,the results show that the method with the lilliefors test can identify the effective charge signals produced in the initial stage of coal loading.The charge signals of compaction stage are basically white noise.In the elastic stage,a small amount of low amplitude effective charge signals which are difficult to identify and mixed with white noise will be produced,and in the elastic plastic transition stage,a charge signal with easy identification,relatively increased amplitude and poor continuity will be produced.In the plastic stage and failure stage,the effective charge signals increase with the increase of stress drop times and the increase of stress drop amplitude.The fluctuation amplitude of charge signals in the two stages is more intense and the continuity of high amplitude charge signals is stronger.Through time frequency transformation,the main frequency of white noise of charge signals is not less than 50 Hz,the main frequency of charge signals produced by coal fracture is not more than 15 Hz,and the FIR low pass filter designed can effectively reduce the noise signals and retain the high amplitude and fluctuation signals.Three evaluation indexes of charge accumulation,average charge intensity and charge variation coefficient are established,which can reflect the fracture state of coal body.Mean charge intensity can also reflect the stress level of coal body.The variation coefficient can more accurately identify the precursor points of coal body entering the accelerated failure stage.Under the influence of mining,the coefficient of variation of charge and the average charge intensity of each measuring point in the field are obviously larger than those without mining influence,and the coefficient of variation of charge decreases gradually with the distance from the working face,and the average charge intensity reaches the maximum value in the range of the peak influence of the abutment pressure at the advanced working face.It shows that the charge monitoring method can obtain the situation of dynamic failure of roadways.It can provide a new monitoring mean for the early warning of coal mine dynamic disasters.