动静组合载荷下卸荷岩石力学特性分析

为研究深部地下工程围岩开挖卸载后又受到动力扰动的力学行为，利用动静组合加载SHPB试验系统对砂岩试件进行静载荷加卸载后再冲击试验。试验过程中，先对岩石试件施加不同的三轴载荷，围压按2，4，6，8 MPa加载，轴向载荷加载到对应三轴静载抗压强度的95%左右，再分别卸载至对应三轴静载抗压强度的20%，30%，60%，70%，80%和90%，然后沿轴向进行同一幅值的冲击载荷试验。试验结果表明：当岩石加卸载到对应三轴静载抗压强度的90%左右，岩石均匀化假设不太适用；动静组合载荷下岩石试件抗压强度随围压增大而增大，当围压不变时，随轴向静压增大出现先增大后减小的趋势；岩石破坏吸收的冲击能随轴向静压的增大逐渐减少，随围压增大而增加。

Mechanical characteristics of unloading rock under coupled dynamic and static loads

In order to study the mechanical behaviors of the surrounding rock of underground projects subjected to dynamic disturbance after excavation, sandstone specimens are loaded, unloaded, secondarily loaded and impacted by use of the coupled dynamic and static loading split hopkinson pressure bar (SHPB) system. Firstly, the sandstone specimens are loaded with different triaxial compressions, confining stresses of 2, 4, 6, 8 MPa, and axial compression stress of 95% of the corresponding triaxial static compressive strength. Secondly, they are unloaded to 20%, 30%, 60%, 70%, 80% and 90% of the corresponding triaxial static compressive strengths. Finally, the impact loading tests with the same amplitude along the axial direction are carried out. From the experimental results, when loading and unloading to 90% of the corresponding triaxial static compressive strengths, the rock homogenization hypothesis is not applicable. The compressive strength of rock increases with the confining pressure when loaded under coupled dynamic and static stresses. When the confining pressure is constant and the axial static pressure increases, the compressive strength of rock increases at first and then decreases. The impactenergy absorbed by rock failure gradually decreases with the increasing axial static pressure and increases with the increasing confining pressure.