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.