Experimental Investigation On Shear Mechanical Behavior Of Single-fractured Sandstone Under Normal Unloading

The mechanical essence of human engineering activities such as mining,tunnel,side slope,petroleum drilling projects are unloading the rock mass,and unloading failure is an important form of failure in rock engineering.In addition,shear failure is one of the basic failure forms of rock,whether under loading or unloading conditions.Therefore,the study of rock shear mechanical behavior under unloading has important engineering and theoretical significance.In view of this,the paper is in combination with National Natural Science Foundation Project "Study on the rheological properties and aging propagated mechanism of hard fractured rock under high residual stress".The method is designed for direct shear test under normal unloading.Red sandstone is used to prepare single fracture samples.The deformation characteristics,strength characteristics and fracture evolution mechanism of single fractured sandstone under uniaxial compression test,direct shear test and direct shear test under normal unloading are studied.The main research contents and achievements of this paper are as follows.(1)A direct shear test under normal unloading was proposed,which can simulate the shear failure under normal unloading.Single-fractured sandstones were tested to investigate the shear mechanical behavior under different test conditions.(2)Direct shear test was carried out for single-fractured sandstone samples to obtain the strength characteristics.The maximum and minimum shear strength of single-fractured sandstone samples were determined.Then the value of the initial shear stress of the direct shear test under unloading is determined.In order to cope with the deformation and strength characteristics and failure mode in direct shear test under normal unloading,the influence of fracture inclination on the deformation characteristics and fracture mode in direct test were studied.(3)The direct shear tests under normal unloading with the same initial shear stress,different initial normal stress and the same initial normal stress and different initial shear stress were carried out.The deformation and strength characteristics are described,among them,deformation characteristics mainly include four normal displacement and two shear displacement,strength characteristics mainly include failure normal stress and amount of unloading.The influence of initial stress and fracture inclination on deformation and strength characteristics is discussed systematically.(4)The fracture evolution process of rock mass was recorded by the video recorder,and the fracture evolution process of rock mass was illustrated by the combination of photographs and sketches.The ultimate failure mode of rock mass was analyzed,and the failure mode of rock mass was summarized,and the influence of fracture inclination on failure mode wss studied.Further,the differences of failure mode with the direct shear test was studied.