真三轴加卸载条件下组合煤岩冲击破坏特征研究

Research on impact failure characteristics of coal-rock combination bodies under true triaxial loading and unloading conditions

采用真三轴试验系统对煤岩组合体开展加卸载实验,探究不同煤厚比例组合体的力学行为响应特征,分析煤厚比例对组合体冲击破坏特征的影响规律。结果表明:(1)随着煤厚比例的增加,试样形成较多的X型共轭剪切裂纹,强度呈现出明显的下降趋势,下降梯度逐渐减小,冲击破坏特征逐渐明显;(2)试样变形主要发生在初始应力加载阶段及垂向应力再加载阶段,最大主应变是试样变形的最主要构成部分;(3)不同煤厚比例试样的全应力–应变曲线特征相似,随着煤厚比例的增加,试样的塑性变形逐渐增加。根据实验结果分析,在开采及地质条件相似情况下,底板冲击趋势随底煤厚度的增加而增加,增加梯度逐渐降低;当底煤厚度增加到一定程度时,底煤厚度的再增加对底板冲击无明显叠加影响。研究成果可为深入认识底板冲击地压发生机制及建设防控技术中试平台并开展工程仿真研究提供参考。

Loading and unloading experiments on coal-rock combination bodies were carried out by a true triaxial test system to explore the mechanical behavior response characteristics of the combination bodies with different coal thickness proportions and to analyze the influence of the coal thickness proportion on impact failure characteristics of combination bodies.The results show that,as the proportion of the coal thickness increases,many X-shaped conjugate shear cracks form in the bodies,the strength shows a significant decrease trend with a gradually decreasing gradient,and the impact failure characteristics gradually become obvious.The deformation mainly occurs in the initial stress loading stage and the vertical stress reloading stage,and the maximum principal strain plays a dominant role in deformation.The characteristics of the full stress-strain curves of combination bodies with different coal thickness proportions are similar.As the proportion of the coal thickness increases,however,the plastic deformation gradually increases.According to the experimental results,under similar mining and geological conditions,the burst trend of the floor increases with a gradually decreasing gradient as the bottom coal thickness increases.When the bottom coal thickness increases to a certain value,the increase of the bottom coal thickness has no obvious superimposed effect on floor burst.The research results can provide a reference for further study of occurrence mechanisms of floor burst,the construction of pilot test platform for prevention and control technology,and the development of engineering simulation.