冲击速度和轴向静载对红砂岩破碎及能耗的影响

地下岩体工程爆破开挖中，距爆源不同距离处岩体承受的地应力和动载荷大小不同，从动载荷的角度表征岩石动态破坏结果与工程实际更吻合。为研究动载荷和地应力大小对岩体破碎和能量耗散特性的影响，利用动静组合加载试验装置，分别设置7个冲击速度和轴向静应力等级，对红砂岩试件进行冲击试验。根据试件的破碎状况，分析不同静应力工况下冲击速度对岩石破坏模式和机理的影响。计算不同工况下的应力波能量值，研究冲击速度和轴向静应力对岩石能耗特性的影响。对破坏试件进行筛分试验，研究岩石破碎分形维数随冲击速度和轴向静应力的变化关系。结果表明，随着冲击速度的增大，试件的破坏程度逐渐加大。无轴压时岩石试件破坏后整体仍是一个圆柱体，属于张拉破坏；有轴压时岩石试件宏观破坏后呈沙漏状，属于拉剪破坏。岩石耗散能随冲击速度的升高呈二次函数关系递增；轴向静应力越高，递增幅度越小。随着冲击速度的升高，岩石分形维数由零逐渐增加；随着轴向静应力的升高，分形维数由零转为大于零的临界冲击速度先升高后降低。

Effect of impact velocity and axial static stress on fragmentation and energy dissipation of red sandstone

Due to the excavation unloading effect and the amplitude attenuation of stress wave, the rock masses locating the different distances away from the blasting source are subjected to different geostress and impact loadings during the blasting excavation of underground rock mass. The construction of relationship between rock dynamic failure properties with impact loadings has more important engineering practical significance compared with representating them with strain rate. In order to investigate the effect of the values of impact loading and the geostress on the characteristics of rock failure and energy dissipation, impact experiments of red sandstone were carried out with a modified split Hopkinson pressure bar testing system, the impact velocities and axial static stresses were set seven levels, respectively. The effects of impact velocity on the failure mode and mechanism of red sandstone under different axial static stresses were researched based on the broken rock specimens. By analyzing the energy values of stress waves under different experimental conditions, the effects of the impact velocity and the axial static stress on energy dissipation of red sandstone were investigated. The fragment fractal dimensions of red sandstone under different impact velocities and axial static stresses were studied based on the sieve test results of the broken specimens. The results show that the increase of impact velocity will aggravate the destroy degree of the red sandstone. The main part after macroscopic failure remains a circular cylinder when a red sandstone specimen is subjected to impact loading and no axial static stress, the failure of the specimen is resulted from its insufficiency of resistance to tensile deformation; but the main part after macroscopic failure represents a hourglass shape when the specimen is under coupled axial static stress and impact loading, the failure mechanism is mixed tension and shear fracture. The dissipation energy of the red sandstone increases in a quadratic function with increasing the impact velocity, the higher the axial static stress, the smaller the increasing amplitude. With the increase of impact velocity, the fractal dimension of the red sandstone increases from zero gradually. For a rock specimen subjected to specific axial static stress, there is a critical impact velocity which signifies that the fractal dimension of the specimen will change from zero to greater than zero, and the critical impact velocity increases first and then decreases with the increase of axial static stress.