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深部构造煤破裂过程的能量演化特征及其差异性分析

Characteristics and differential analysis of energy evolutin of deep tectonic coal during fracturing processes

  • 摘要: 构造煤在扰动作用下稳定性和破坏方式与原生煤存在差异。为探究深部构造煤破裂过程的能量演化特征及其差异性, 利用不同加载路径及声发射监测、计算机断层扫描(CT扫描)重建和微震监测技术分析了构造煤细观参数、宏观力学参数、能量分配及现场构造煤赋存地层微震特征。研究表明: ①构造煤细观结构与原生煤不同, 构造煤表面形貌平整度差, 碎屑较多, 含有阶梯状断口, 构造煤细观结构使之表现出与原生煤不同的宏观力学行为, 细观参数与宏观力学参数之间具有线性相关关系; ②构造煤受载后特征应力阶段与原生煤差别较大, 弹性阶段和裂纹稳定扩展阶段较短, 煤样原生裂隙导致劣化强度不同, 但达到一定值后会出现相似的裂纹发展; ③构造煤破裂更为分散, 受循环荷载影响较大, 无论加载路径如何, 构造煤均易发展大尺度裂纹且裂纹发展更无序; ④构造煤易发生剪切破裂且裂纹弯折, 破坏所消耗的能量较多, 碎裂煤在循环加卸载过程中耗弹比减小, 释放的能量占比增加, 强度折减度最高; ⑤原生煤区低能量微震少, 构造煤区低能量微震较多。构造煤所在地层微震事件多发, 原生煤所在地层微震事件更为突发, 尤其注意碎裂煤区。根据室内试验结果可解释现场采区微震监测数据, 为实际构造煤所在地层危险预警提供理论支撑。

     

    Abstract: The stability and failure modes of tectonic coal under disturbance differ significantly from those of original coal. To investigate the energy evolution characteristics and disparities during the fracturing process of deep tectonic coal, the mesoscopic parameters, macroscopic mechanical properties, energy distribution of tectonic coal and microseismic characteristics in tectonic coal-bearing strata were analyzed through various loading paths combined with acoustic emission monitoring, computed tomography (CT scan) reconstruction and microseismic monitoring. The result shows distinct microstructural differences exist between tectonic and origin coal, manifested as poor surface regularity, abundant debris accumulation and stepped fractures in tectonic coal. These microstructural characteristics lead to divergent macroscopic mechanical behaviors, with linear correlations between mesoscopic and macroscopic parameters. Tectonic coal exhibits substantially different characteristic stress stages under loading when compared to origin coal, showing shorter elastic phases and stable crack propagation periods. While primary fractures induce varying degradation intensities, similar crack development patterns emerge beyond critical stress thresholds. Tectonic coal demonstrates more dispersed fracturing patterns with greater susceptibility to cyclic loading effects. Regardless of loading paths, tectonic coal tends to develop large-scale cracks with more disordered spatial distributions. Shear-dominated failures with tortuous crack paths prevail in tectonic coal, requiring higher energy consumption. The elastic energy dissipation ratio decreases during cyclic loading-unloading processes in fractured coal, accompanied by increased proportions of released energy and maximum strength reduction. Microseismic monitoring shows fewer low-energy events in primary coal zones when compared to tectonic coal areas. Tectonic coal-bearing strata exhibit higher microseismic frequency with gradual energy release patterns, while origin coal strata demonstrate more sudden seismic events, particularly requiring attention in fractured coal zones. The findings interpret field microseismic data and help early warning systems development for tectonic coal-bearing strata hazards.

     

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