轴、侧向同卸荷下砂岩力学特性影响的试验研究

本文以实际岩体工程为背景，利用WDT-1500 仪器开展了轴向、侧向同时卸荷条件下砂岩的三轴试验. 结果表明:轴、侧向同卸荷这种卸荷路径下，砂岩试样破坏时并没有出现应力峰值，为了定义试样的破坏强度，将最大与最小主应力差随最小主应力的变化关系曲线上应力跌落的拐点处的应力值定义为破坏强度. 砂岩变形初始段发生应力跌落和轴向应变回弹，破坏前无明显的弹性和屈服阶段；试验的过程中，砂岩的侧向变形明显大于轴向变形，其体积应变一直处于膨胀状态；相对于砂岩的常规三轴试验结果，试样破坏时的强度在轴向、侧向同时卸荷条件下有所降低. 初始轴压和初始围压对试样的力学特征有十分显著的影响，但围压的卸荷速率却并不显著. 砂岩的破坏特征主要是以张-拉为主的混合张剪的破坏. 

EXPERIMENTAL STUDY ON MECHANICS CHARACTERISTICS OF SANDSTONE UNDER AXIAL UNLOADING AND RADIAL UNLOADING PATH

This article take the actual rock mass project as a background, triaxial compression for sandstone specimen under axial unloading and radial unloading—this path is realized on WDT-1500 reactive material testing machine. The test results show that the failure of sandstone specimen don’t appear peak stress under axial unloading and radial unloading—this path, to define the inflection point of stress drop of (The maximum principal stress-minimum principal stress)～the minimum principal stress curves of sandstone for failure strength. The stress drop and the axial strain of resilience of sandstone specimens were happened under axial unloading and radial unloading, which had no obvious elasticity and yield step before rock specimens’ failure. The lateral deformation is larger than the axial deformation in the process of test,and volumetric strain of the sandstone specimen is always in a state of expansion. The strength of sandstone is reduced relative to triaxial compression. the deformation property and strength property of sandstone under this path are mainly influenced by initial axial pressure and initial radial pressure,but the influence of the unloading speed of radial pressure is not clear. The failure characteristics of samples often present mixed zhang-shear failure under axial unloading and radial unloading.