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不同加卸载路径下冲击倾向性煤岩组合试件破坏特征研究

Study on failure characteristics of coal-rock composite specimens with impacttendency under different loading and unloading paths

  • 摘要: 冲击地压矿井采掘扰动下煤岩体破坏特征复杂,严重影响了冲击地压的监测预警与防控,开展冲击倾向性煤岩组合体在不同加卸载应力路径下的破坏及声发射特征研究,对促进冲击地压的精准监测与防控具有重大意义。以冲击危险性煤岩组合体试件为研究对象,采用岩石力学单轴试验机和声发射监测系统进行了常规单轴加载和不同循环加卸载试验,分析了煤岩组合体在不同应力路径下的力学性质及能量演化规律,研究了煤岩组合体声发射试件数与应力路径特征关系,并以此计算研究了b值和熵值的演化趋势,讨论了经历不同应力路径下煤岩体对应到工程现场的冲击地压研究。研究结果表明:煤岩组合体在常规加载下峰值强度最大,变下限加卸载次之,恒下限加卸载峰值强度最小;试件中煤体为X状共轭斜面剪切破坏,岩石为拉伸破坏;恒下限加卸载下试件损伤程度较高,低能量的状态输入能量后失稳破坏,变下限加卸载下试件处于高能状态输入更多的能量后失稳破坏。获得了声发射事件数、b值及熵值的演化规律及其与破坏行为之间的关系,声发射事件数随加载强度的增加逐步上升,循环加卸载声发射事件数分布随应力路径的变化表现出波动特性,累计声发射曲线呈阶梯式增长;恒下限循环加卸载下b值和熵随加卸载表现出的波动性循环特征更明显,而变下限循环加卸载在应力较高的循环中表现出波动性特征,不同应力路径下试件临近失稳破坏的共同特征为b值处于低值波动,熵值在较高水平波动。较高的采掘强度会导致煤岩体在较短时间内经历不充足的自我卸压,因而裂隙扩展释放的能量较大;较低的采掘强度使煤岩体有充足的时间进行自我卸压,裂隙扩展释放的地音能量较小。根据不同加卸载作用下煤岩体破坏特征及声发射事件数、b值、熵值的演化规律,可有效的预测煤岩体破坏行为。较低的采掘强度使煤岩体有充足的时间进行自我卸压,裂隙扩展较为频繁,地音能量释放较小。研究结果为不同采动强度的采掘方式合理选取提供了依据,在实际工程应用中可为冲击地压矿井的实现精准监测与防控提供支撑。

     

    Abstract: The failure characteristics of coal and rock mass under mining disturbance in rock burst mine are complex, which seriously affects the monitoring, early warning and prevention of rock burst. It is of great significance to study the failure and acoustic emission characteristics of rock burst prone coal-rock combination under different loading and unloading stress paths. Taking the impact-dangerous coal-rock composite specimens as the research object, the conventional uniaxial loading and different cyclic loading and unloading experiments were carried out by using the uniaxial testing machine of rock mechanics and the acoustic emission monitoring system. The mechanical properties and energy evolution law of coal-rock composite under different stress paths were analyzed, and the relationship between the number of acoustic emission specimens of coal-rock composite and the characteristics of stress paths was studied. Based on this, the evolution trend of b value and entropy value was calculated and studied, and the study of rock burst corresponding to the engineering site under different stress paths was discussed. The results show that the peak strength of coal-rock combination is the largest under conventional loading, followed by variable lower limit loading and unloading, and the peak strength of constant lower limit loading and unloading is the smallest. The coal in the specimen is X-shaped conjugate slope shear failure, and the rock is tensile failure. Under constant lower limit loading and unloading, the damage degree of the specimen is higher, and the specimen is unstable and destroyed after inputting energy in low energy state, and it is unstable and destroyed after inputting more energy in variable lower limit loading and unloading state. The evolution law of acoustic emission events, b value and entropy value and their relationship with failure behavior are obtained. The number of acoustic emission events increases gradually with the increase of loading intensity, and the distribution of acoustic emission events in cyclic loading and unloading shows fluctuation characteristics with the change of stress path, and the cumulative acoustic emission curve increases step by step. Under constant lower limit cyclic loading and unloading, the fluctuation cycle characteristics of b value and entropy with loading and unloading are more obvious, while under variable lower limit cyclic loading and unloading, it shows fluctuation characteristics in cycles with higher stress. The common characteristics of specimens near instability and failure under different stress paths are that B value fluctuates at a low value and entropy value fluctuates at a high level. Higher mining intensity will lead to insufficient self-pressure relief of coal and rock mass in a short time, so the energy released by fracture expansion is greater; The lower mining intensity allows the coal and rock mass enough time for self-pressure relief, and the ground sound energy released by crack expansion is small. According to the failure characteristics of coal and rock mass under different loading and unloading effects and the evolution law of acoustic emission event number, b value and entropy value, the failure behavior of coal and rock mass can be effectively predicted. The lower mining intensity makes the coal and rock mass have enough time to self-decompress, the cracks expand more frequently, and the ground sound energy is released less. The research results provide a basis for reasonable selection of mining methods with different mining intensities, and can provide support for accurate monitoring and prevention and control of rock burst mines in practical engineering applications.

     

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