煤体静载破坏中低频磁场变化特征及产生机制研究

Characteristics and generation mechanism of low-frequency magnetic field generated during the damage of coal under static load

为了研究煤体静载破坏中低频磁场变化特征及其产生机制,进一步完善煤矿动力灾害监测预警技术,通过室内试验、现场试验研究了煤体静载破坏中低频磁场时、频谱特征,并结合微震信号提出了低频磁信号的产生机制。结果表明:煤体静载破坏中所产生低频磁场信号强度为19～156 nT,信号最大幅值、能量与试样强度、加载速度均呈正相关关系。垂直于裂纹扩展面磁场最强,平行于裂纹扩展面磁场最弱。并结果微震信号提出了低频磁场产生机制。低频磁场与微震信号具有时、频域同步性,带电裂纹面随微震信号同频振荡为低频磁场产生机制。现场放炮破煤低频磁信号由簇状脉冲信号及小幅震荡信号组成,其中簇状脉冲成分产生于炮后振动波带动带电壁面的同频振动,而小幅震荡成分是巷帮煤壁趋向新应力平衡状态时发生的横向拉伸破坏及带电煤碎屑运移、摩擦及转动的结果。

The aim of this paper is to study the characteristics and generation mechanism of the low-frequency magnetic field generated during the damage of coal under static load, and to complete the monitoring and warning technology of dynamic disasters in coal mine. Laboratory and field experiments were conducted to analyse the characteristics in time and frequency domain of low-frequency magnetic signal. Laboratory experiment results show that the strength of the generated magnetic field is in the range of 19-156 nT. Both the maximum amplitude and magnetic field energy have a positive correlation with the intensity of coal and loading speed. It also shows that the magnetic field perpendicular to crack surface is the strongest, while the magnetic field parallel to the crack surface is the weakest. Then, by combining with the micro-seismic signal, generation mechanism of the low-frequency magnetic field was proposed. Results reflect that the magnetic signal and micro-seismic signal are synchronous in the time and frequency domain, and oscillation of crack surface with charge leads to low-frequency magnetic field. Field test results indicate that the magnetic signal includes the cluster pulse signal and small amplitude oscillation signal. The cluster pulse signal is caused by the crack surface vibration generated from blasting. The small amplitude oscillation signal is the result of lateral tensile failure generated during the formation process of the new stress equilibrium in coal wall, and migration, friction and rotation of coal particles with charge.