Study on dynamic deformation modulus of rock under confining pressure unloading and dynamic loading
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摘要: 利用SHPB岩石动静组合加载实验系统，研究在不同轴压水平下围压以1 MPa/s速率卸载至预加值50%时矽卡岩受频繁冲击作用的动态变形模量变化规律。实验结果表明：高轴压促使岩石内部微裂纹萌发与扩展，降低了岩石抵抗外部冲击的能力。围压的侧向约束阻碍岩石内部裂纹的横向扩展，但在围压卸载时会加剧岩石内部的损伤，这是由于高轴压下，围压卸载导致岩石内部应力重新分布。轴压与围压卸载共同影响着冲击作用下的岩石动态变形模量，通过岩样在冲击荷载下的能量耗散分析岩石动态变形模量的变化规律，有助于了解深部岩体开挖的破坏机制。Abstract: Dynamic experiments on skarn were conducted with a modified one-dimensional coupled static and dynamic loads based on SHPB device. The variations of dynamic deformation modulus of skarn under different axial pressures and frequent dynamic disturbance are studied when confining pressure was unloaded at the 1 MPa/s rate to 50% of initial value. The results show that high axial pressure promotes the formation and propagation of microcracks in rocks and reduces the resisting ability under external shocks. The lateral restraint of confining pressure hinders the transverse propagation of cracks inside the rock, but it will aggravate the damage when confining pressure is unloaded. This is because, under high axial pressure, unloading of confining pressure results in redistribution of stress inside rock. The axial pressure and confining unloading pressure affect the dynamic deformation modulus of rock under impact. Base on the variation analysis of dynamic deformation modulus by the energy dissipation of rock under impact, some significant understanding of deep rock excavation failure mechanism are drawn.
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图 1 基于SHPB装置的动静组合加载系统
Figure 1. Coupled static and dynamic loading system based on SHPB device
图 2 围压卸载过程中频繁冲击荷载下矽卡岩的动态应力应变曲线(图中数字表示冲击次序)
Figure 2. Dynamic stress-strain curves of skarn with frequent impact and confining pressure unloading (numbers in figure denotes impact order)
图 3 动态变形模量计算示意图
Figure 3. Schematic diagram of dynamic deformation modulus calculation
图 4 矽卡岩首次受冲击荷载的动态变形模量与轴压的关系
Figure 4. Relationship between dynamic deformation modulusof skarn and axial compression for the first impact
图 5 矽卡岩冲击破坏时的动态变形模量与轴压的关系
Figure 5. Relationship between dynamic deformation modulus of skarn and axial compression in impact failure
图 6 矽卡岩能耗与冲击次数的关系
Figure 6. Relationship between energy dissipation of skarn and impact times
图 7 矽卡岩动态变形模量与围压的关系
Figure 7. Relationship between dynamic deformation modulus of skarn and confining compression
图 8 矽卡岩能耗与冲击次数的关系
Figure 8. Relationship between energy dissipation of skarn and impact times
图 9 不同轴压下动态变形模量与冲击次数的关系
Figure 9. Relationship between dynamic deformation modulus and impact number under different axial compression
表 1 矽卡岩三轴压缩实验结果
Table 1. Results of three axial compression experiment of skarn
围压/MPa 弹性模量/GPa 三轴抗压强度/MPa 峰值应变/10-3 黏结力/MPa 内摩擦角/(°) 15 26.81 217.93 10.27 6.86 57 20 32.69 237.87 12.29 25 21.81 245.06 14.37 30 22.03 284.34 15.38 
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表 2 实验方案
Table 2. Testing projects
岩样编号 预加轴压/MPa 预加围压/MPa 冲击时围压/MPa 围压卸载速率/(MPa·s-1) 冲击气压/MPa XK1-1 52.5 15 7.5 1 0.6 XK1-2 20 10.0 XK1-3 25 12.5 XK1-4 30 15.0 XK2-1 62.5 15 7.5 1 0.6 XK2-2 20 10.0 XK2-3 25 12.5 XK2-4 30 15.0 XK3-1 72.5 15 7.5 1 0.6 XK3-2 20 10.0 XK3-3 25 12.5 XK3-4 30 15.0 XK4-1 82.5 15 7.5 1 0.6 XK4-2 20 10.0 XK4-3 25 12.5 XK4-4 30 15.0
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