煤单轴峰后动态冲击破坏特征及差异机制模拟研究

Numerical simulation on difference mechanism and post-peak dynamic failure characteristics of coal under uniaxial compression

  • 摘要: 煤岩冲击倾向性鉴定是冲击地压防治的重要基础,而鉴定结果与煤峰后动态破坏的应力降形态密切相关。针对煤单轴动态冲击破坏应力降特征及差异机制开展研究,综合利用MTS试验机、高速摄像机和声发射监测系统,开展了冲击倾向性煤单轴动态冲击破坏的声发射定位试验,得到了煤单轴应力−应变曲线,捕捉了煤峰值前后动态冲击破坏过程,同步监测了声发射微破裂的时空强分布信息,归纳了煤峰后动态冲击破坏3种典型类型,开展了预制软弱结构面的PFC3D三维精细数值模拟,反演再现了煤峰后3种典型冲击破坏和能量演化过程,揭示了峰后应力降形态的差异机制,模拟结果与实测冲击破坏相一致。结果表明:①煤峰前裂隙加速扩展阶段和峰后阶段的应力降形态迥异,峰后可归纳为单次应力降、2次应力降和多次应力降型3种典型冲击破坏模式;②大能量微破裂事件时空集聚分布与峰后瞬间动态破坏的时空分布相一致,峰后单次应力降型煤样在峰前裂隙加速扩展阶段发生较大尺度的应力降,有效承载面积已显著降低,其峰后声发射绝对能量最高;③原生结构或次生弱面的发育贯穿位置、弱面力学参数不同导致煤样峰前最大损伤水平和峰前煤样残余承载面积存在差异,进而控制煤峰后动态应力降的形态特征;④峰前煤样应变能峰值越高,煤样颗粒弹射动能越小,峰前损伤水平越低,峰后煤样冲击破坏弹射的动能越大,冲击显现越剧烈。研究结果可深入掌握冲击倾向性煤峰后动态破坏应力降差异机制,为煤体冲击倾向性评价提供参考。

     

    Abstract: The identification of coal rock burst tendency is an important foundation for the prevention and control of rock burst, and the identification results are closely related to the stress drop pattern of dynamic failure after coal peak. A study was conducted on the stress drop characteristics and differential mechanisms of coal with impact propensity post-peak dynamic failure. By comprehensively utilizing MTS testing machines, high-speed cameras, and acoustic emission monitoring systems, an acoustic emission localization test was conducted for uniaxial dynamic impact failure of coal with impact propensity. The uniaxial stress-strain curve of coal was obtained, capturing the dynamic impact failure process before and after the coal peak, and synchronously monitoring the spatiotemporal strongly distributed information of acoustic emission micro fracture. Three typical types of dynamic impact failure after coal peak were summarized, and PFC3D three-dimensional fine numerical simulation of prefabricated weak structural surfaces was carried out. The three typical impact failure and energy evolution processes after coal peak were inverted and reproduced, revealing the differential mechanism of stress drop morphology after peak. The simulation results are consistent with the measured impact failure. The results indicate that: ① the stress drop patterns in the pre peak and post peak stages of coal fractures were significantly different, and could be summarized into three typical impact failure modes: single stress drop failure mode, double stress drop failure mode, and multiple stress drop failure mode; ② The spatiotemporal concentration distribution of high-energy micro fracture events was consistent with the spatiotemporal distribution of instantaneous dynamic failure after the peak. The single strain drop failure coal sample after the peak had undergone a large-scale stress drop during the accelerated crack expansion stage before the peak, and the effective bearing area has significantly decreased. The absolute energy emitted by the sound after the peak is the highest; ③ The development of primary or secondary weak planes throughout the location leads to differences in mechanical parameters of weak planes, resulting in variations in the maximum pre-peak damage level and residual bearing area of coal samples, which in turn control the morphological characteristics of the post-peak dynamic stress drop in coal; ④ The higher the peak strain energy of the pre-peak coal sample, the lower the kinetic energy of the coal sample particle ejection, the lower the pre-peak damage level, and the higher the kinetic energy of the post-peak coal sample impact damage ejection, indicating a more severe impact. The research results can provide a deep understanding of the differential mechanism of dynamic failure stress drop after the peak of impact prone coal, providing a reference for the evaluation of impact prone coal bodies with weak structural planes.

     

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