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单轴压缩条件下强冲击倾向性煤体失稳特性及弹射模式研究

Characteristics of instability and ejection modes of coal exhibiting strong impact inclination under uniaxial compression

  • 摘要: 为探究冲击倾向性煤单轴压缩作用下的变形、破裂及弹射破坏力学行为,开展了不同加载速率下冲击倾向性煤的单轴压缩试验,获取了煤样的峰后应力跌落分类特征,结合煤样CT扫描原生裂隙三维重构,分析了不同应力跌落类型煤样的失稳破坏差异机制。基于非接触全场应变测量结果,分析了煤样裂隙的峰前、峰后破裂演化及破裂−弹射规律,统计计算了煤样弹射区域的应力变化及转换特征,揭示了煤体的弹射模式,获取了煤样应力跌落类型的破裂−弹射及弹射模式分类特性,分析了煤样现有冲击倾向性指数与峰后弹射冲击动能的关联性,并建立了表征煤样峰后弹射剧烈程度的指标Wsdr。结果表明:煤样峰后应力跌落分为持续跌落(Ⅰ类)、台阶式跌落(Ⅱ类)及瞬间跌落(Ⅲ类)3种类型,且煤样的峰后应力跌落类型与其原生裂隙发育密切相关。冲击倾向性煤弹射前表面裂隙扩展具有缓慢、加速扩展破裂的非线性特征,且Ⅰ、Ⅱ、Ⅲ类弹射冲击孕育时间依次减小。冲击倾向性煤分为局部弹射、区域贯通弹射和整体失稳弹射3种弹射类型,Ⅰ、Ⅱ、Ⅲ类煤样分别表现为以局部弹射、区域贯通弹射、整体失稳弹射为主导发生弹射冲击;煤样具有母体动力源和弹射块体动力源2类弹射模式,且同一应力跌落类型煤样可由母体动力源或弹射块体动力源导致弹射冲击。提出的指标Wsdr与弹射弹射动能呈线性正相关。

     

    Abstract: Mechanical behaviors of deformation, rupture, and ejection failure of coal with impact inclination under uniaxial compression were investigated. Uniaxial compression tests were conducted on coal with impact inclination at different loading rates. The classification characteristics of post-peak stress drop in coal samples have been identified. Based on the 3D reconstruction of the primary fracture of coal samples through CT scanning, the distinct mechanisms of instability failure of coal samples with various stress drop types are analyzed. Based on the non-contact full-field strain measurement results, the pre-peak and post-peak fracture evolution and the fracture-ejection rule of coal samples are analyzed. The stress change and transformation characteristics of the coal sample ejection region are statistically calculated. The ejection mode of the coal body is disclosed, and the classification characteristics of the fracture-ejection and the stress drop type of the coal sample ejection mode are obtained. Additionally, the correlation between the existing impact tendency index of coal sample and the impact kinetic energy of post-peak ejection is analyzed, and Wsdr is established to characterize the intensity of post-peak ejection of coal sample. The results show that: Post-peak stress drop of coal samples can be divided into three types: continuous drop, stepped drop and instantaneous drop, and the post-peak stress drop type of coal samples is closely related to the development of primary fractures. Surface crack propagation before the impact inclined coal ejection has the nonlinear characteristics of slow and accelerated crack propagation, and the incubation time of class Ⅰ, class Ⅱ and class Ⅲ impact ejection decreases successively. Coal with impact inclination can be classified into local ejection, regional through-out ejection and global instability ejection. Coal samples of Class Ⅰ, Ⅱ and Ⅲ are dominated by local ejection, regional through-out ejection and global instability ejection respectively. The coal sample has two types of ejection modes: parent power source and ejection block power source. The same stress drop type coal sample can be caused by parent power source or ejection block power source. Proposed index Wsdr has a linear positive correlation with the ejection kinetic energy.

     

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