煤岩失稳破坏前兆电磁信号优势特征频率及应用基础研究

The variation of the electromagnetic(EM) signal's frequency can directly reflect the evolution of coal and rock internal damage. In order to study the relationship between frequency variation and coal and rock damage and failure, and to explore the precursory EM signal's dominant characteristic frequency of the instability and failure of coal and rock and its characteristics, this project intends to conduct synchronization test to study the multi-frequency (ULF~VHF bands) EM response characteristics and laws during the whole stress-strain process of different types of coal and rock under different loading types, to study the frequency shift characteristics and dominant frequencies under different stress levels, and to determine the dominant characteristic frequency and its characteristics precursor to the coal and rock bursting with different lithologies and under different dynamic processes. After that, we will research the frequency shift mechanism of EM signal during the coal and rock instability and failure process; the correlations between EM response with different bands, frequency shift and coal and rock mechanics and internal damage; and then build a frequency shift-based coupling model of stress, EM response and energy for coal and rock damage and failure. Finally, we will conduct synchronization test to study the multi-frequency EM response and signal frequency shift of the large-scale coal rock mass dynamic instability and evolution process, to establish the relationship between the dominant frequency of EM signal and the stress state and the risk degree of coal rock mass, and to propose a coal rock mass stability assessment and critical instability identification method based on dominant characteristic frequency and its characteristics. The results are of important theoretical and practical significance in further understanding of multi-frequency EM radiation generation mechanism, and refined studying the EM radiation directional monitoring and dangerous source positioning technology.

本项目拟同步测试研究不同类型煤岩不同加载方式下全应力-应变过程的多频（ULF~VHF频段）电磁响应特征规律，研究该过程电磁信号频移特征及不同应力水平下的优势频率，确定不同岩性、不同动力过程煤岩破裂前兆的优势特征频率及其特性；结合损伤力学、电磁动力学等理论研究煤岩失稳破坏过程电磁信号频移机理，研究不同频段电磁响应、信号频移与煤岩力学特性及内部损伤的相关性，依此建立基于信号频移的煤岩损伤破坏力-电-能耦合模型；同步测试研究大尺度煤岩体动力失稳演化过程多频电磁响应及信号频移规律，建立电磁信号优势频率与煤岩体应力状态及危险程度的关系；在上述研究工作的基础上，初步提出基于电磁信号优势特征频率及特性的煤岩体稳定性评估及临界失稳辨识方法。研究成果对进一步认识多频电磁辐射产生机理，促进煤岩电磁辐射定向监测及危险源定位技术的精细化研究具有重要的理论及现实意义。

电磁信号频率作为最基本的信号参数之一，能够直接反映煤岩内部损伤演化过程。为了研究信号频率与煤岩损伤破坏的关系，探索煤岩失稳破坏前兆电磁信号优势特征频率及特性，本项目系统开展了煤岩失稳破坏前兆电磁信号优势特征频率及应用基础的研究工作。发表学术论文10篇，出版专著1部，申请国家发明专利3项，授权1项，联合培养并毕业博士生1名，硕士生2名。主要创新成果如下：.(1)建立了煤岩破坏多频电磁响应综合测试系统，同步测试研究了不同类型煤岩不同加载方式下全应力-应变过程的多频（ULF~VHF频段）电磁响应特征规律。发现：a.受载煤体能够产生多个频段的电磁辐射。b.煤样在加载过程中，电磁信号存在显著的频移特性，信号主频呈现先增大后减小的趋势：加载前期没有明显的主频带；煤样进入线弹性变形阶段时，信号主频逐步增大并保持在60 kHz左右；峰值载荷前后试样发生主破裂前信号主频向低频移动，主频低于20kHz。c.当外载荷较大时，电磁信号强度也相应增大且更加丰富，表现在频谱图上为在更宽的频带上出现强度较大的电磁信号。.(2)研究揭示了煤岩失稳破坏过程电磁信号频移机理，得到了不同频段电磁响应、信号频移与煤岩力学特性及内部损伤的相关性，建立了基于电磁信号频移的煤岩损伤破坏力-电-能耦合模型。发现：电磁信号频率与裂纹尺寸、材料密度、弹性模量、泊松比及强度等物理力学参数密切相关。对同一煤样加载时，由于其它参数保持不变，其信号频率的变化与内部裂纹尺寸的变化有关，即频移这一动态概念与裂纹扩展这一动态过程相对应。.(3)同步测试研究了现场大尺度煤岩体动力失稳演化过程的多频电磁响应及信号频移规律。发现：当受载煤体释放的电磁信号主频处于较低频段或者向较低频段移动时，说明煤体内部有较大尺度的裂纹产生、扩展，其外部承载了较大的应力。基于此，我们可以通过电磁信号频移特征定性判定煤岩体的应力状态。实际中，还可以结合其他边界条件（如是否处于构造带，瓦斯浓度是否异常等）判定煤岩体的稳定性。