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不同应力状态及应变率下组合煤岩体力学特性及能量演化规律

Mechanical properties and energy evolution of combined coal-rock body under different stress states and strain rates

  • 摘要: 深部煤岩体应力环境复杂多变,为进一步揭示动载荷诱发冲击地压的发生机制,采用岩−煤−岩结构试样,利用改进后SHPB试验系统,开展不同应力状态(无轴压及围压、一维动静组合、三维动静组合)及应变率(49.3~137.9 s−1)下冲击试验,研究组合煤岩体试样的强度、变形、破坏特征及能量演化规律。结果表明:无轴压及围压、一维动静组合下组合体试样应力应变曲线峰后存在应力回弹及应变软化2种类型,三维动静组合下都存在应力回弹现象。3种应力状态下试样峰值强度大致随应变率的增加而增加,表现出明显的率相关性。3种应力状态下,都是反射能占入射能的比例最高,透射能占入射能的比例最低;三维动静组合下,反射能占入射能的比例低于其他2种应力状态;当应变率低于123 s−1,能量利用率、耗散能随应变率增加而逐渐增加,耗散能密度随入射能的增加而增加。试样破坏形式表现出明显的率相关性,随着应变率的增加,煤、砂岩碎块尺寸也逐渐变小。无轴压及围压、一维动静组合下试样首先在煤岩界面发生破坏,煤、砂岩产生较多小尺寸碎块是由于峰后二次裂纹造成的。三维动静组合下单次冲击后煤岩体破裂不明显。

     

    Abstract: The stress environment of deep coal-rock mass is complex, to further reveal the mechanism of rock burst induced by dynamic load. Based on the Split Hopkinson Pressure Bar test system, the dynamic tests under different stress states (non-axial and confining loads, one-dimensional coupled static-dynamic loads, three-dimensional coupled static-dynamic loads) and strain rates (49.3~137.9 s−1) were carried by using the rock-coal-rock structure samples. The characteristics of strength, deformation, failure and energy evolution of rock-coal-rock structure samples were studied. The results show that there were two types of stress rebound and strain softening after the peak of the stress-strain curve of the composite specimen under non-axial and confining loads and under one-dimensional coupled static-dynamic loads, and there was stress rebound phenomena under three-dimensional coupled static-dynamic loads. Under three stress states, the peak strength of the samples increases roughly with the increase of strain rate, showing an obvious rate correlation. Under three stress states, the proportion of reflected energy to incident energy was the highest, and the proportion of transmitted energy to incident energy was the lowest. The proportion of reflection energy to incident energy under three-dimensional coupled static-dynamic loads was lower than the other two stress states. When the strain rate is lower than 123 s−1, the energy utilization rate and dissipated energy increase gradually with the increase of the strain rate, and the dissipated energy density increases with the increase of the incident energy. The failure modes of the samples show an obvious rate correlation, and the size of coal and sandstone fragments decreased gradually with the increase of strain rate. Under non- axial or confining loads and one-dimensional coupled static-dynamic loads, the samples firstly failed at the coal-rock interface. Many small size fragments of coal and sandstone are secondary cracks caused by the effect of loads. The fracture of coal and rock mass is not obvious under three-dimensional coupled static-dynamic loads.

     

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