主动围压下地下工程岩石的冲击压缩特性试验研究

 岩石等脆性材料的力学性能与其所受围压的大小密切相关。为了研究地下工程岩石在围压下的冲击压缩特性，采用具主动围压加载的分离式Hopkinson压杆，对岩石进行主动围压下的SHPB冲击压缩试验，得到岩石在不同围压和不同应变率下的轴向应力–应变曲线，并对试验过程中试件的应力均匀性进行分析。研究表明：岩石类脆性材料在围压作用下其抗压强度和韧性大大提高，并且具有向延性特征发展的趋势，显现出较强的围压效应；在同等级围压下，岩石的峰值强度和峰值应变随应变率的变化表现出显著的应变率相关性，动态强度增长因子与应变率的对数呈近似线性关系，动态强度随应变率的增加而近似线性增长。单轴动荷载下，岩石在以拉应力为主，其他应力联合作用下发生破坏，表现出明显的脆性特征；随着围压的增加，岩石试件将发生脆性向延性的转变，破坏形态以压剪破坏为主，同时发生拉应变破坏和卸载破坏。

EXPERIMENTAL STUDY OF SHOCK COMPRESSION PROPERTIES OF UNDERGROUND ENGINEERING ROCK UNDER ACTIVE CONFINING PRESSURE

The mechanical properties of rock-like brittle materials are closely related to the confining pressure. In order to study the dynamic mechanical properties of rock under confining pressure and get its axial stress-strain curve under distinct confining pressures and strain rates，the underground engineering rock are subjected to impact compression experiments with the split Hopkinson pressure bar(SHPB) of diameter 100 mm with active confining pressure device. At the same time，the dynamic stress equilibrium of SHPB experiment is analyzed. Experimental results show that：(1) The dynamic compressive strength and toughening effects of rock are more prominent under confining pressure and appears development trends to ductile characteristic，which reveals a strong confining pressure effect. (2) Under the same range of confining pressure，rock?s peak strength and peak strain change with the strain rate and reveal significant strain rate dependence. The dynamic strength increase factor keeps an approximately linear relationship with the logarithm of strain rate and dynamic strength appears approximately linearly increase with the stain-rate upwards. (3) The rock demonstrates the obvious fragility characteristic under axial dynamic load. It damages under the action of many stresses combined and mainly by the tensile stress. With the confining pressure increasing，the rock sample reverses from brittle to ductile. Failure modes are characterized by compression shear damage going with tensile strain damage and unloading damage.