Experimental Study On Shear Mechanical Properties Of 3D Rough Rock Joint Under Constant Normal Stress Conditions

The high rock slope and the frequent earthquakes are the two most common geological problems in the construction of the projects in the southwest region,China.It is known that the shear deformation along its own structural plane is the most common deformation mode for rock mass projects in the face of the above geological problems.Therefore,a detailed understanding of the shear mechanical behavior of the structural plane is of great significance to guide the engineering practice.Based on the above background,the direct shear and cyclic shear tests and morphology scanning of jointed rock mass were carried out by TAJW-1000 rock shear test system and three-dimensional topography scanner.The evolution laws of shear stress,normal displacement and surface failure characteristics of structural surface under direct load and cyclic load were analyzed.The main research results are as follows:(1)The shape of the shear stress-shear displacement curve under direct shear load mainly depends on the surface morphology of the structural surface and the properties of the filling material,which can be divided into peak type and gentle type.The normal stress and loading rate do not change its shape.In the process of direct shear,the normal deformation of the unfilled structural plane generally presents shear shrinkage first and then dilatancy.In the case of thin-layer filling,the rock joints with smaller roughness presents pure shear shrinkage,and the dilatancy curve of the structural plane with larger roughness presents shear shrinkage first and then dilatancy.(2)The difference in shear stress versus shear displacement curves of three groups of unfilled rock joints is mainly reflected in the cycle 1,which is the same as the results of direct shear tests,can be divided into peak type and gentle type.Later,the curves are shown as gentle type in the subsequent cycles.In the initial several cycles,the shear stress curve evolution trend of infilled rock joints is opposite to that of unfilled rock joint.It is speculated that with the increasing of number of cycles,the shear stress curve will transit back to the yield curve.With or without filling,the maximum stress between corresponding cycles generally follows the trend of increasing with the increase of roughness.(3)The maximum difference of normal displacement evolution law of unfilled rock joints surface lies in the first cycle.With the increase of the number of cycles,the overall normal deformation shows a shear shrinkage state.The average dilatancy angle of rock joints decreases with the increase of the number of cycles,and the distribution of the surface bulge determines the trend of the decrease rate.The deformation of infilled rock joints is mainly manifested as shear shrinkage,and the shear expansion effect is minimal.With the increase of the number of cycles,the average shear expansion angle of the three groups decreases with the deceleration rate.(4)The direct shear failure mode of rock joints is the combination of slip,fracture and tensile failure.The landslide failure mechanism caused by gravity load can be divided into slip-tooth cutting mechanism,tooth cutting-fracture mechanism and interface slip-shear fracture mechanism.(5)Under the cyclic loading,the macroscopic failure characteristics of unfilled rock joints are mainly wear failure and tensile-shear combined failure,and the failure mode of infilled rock joints is mainly the combination of shear slip between filling layers and internal combination-tensile-shear crack damage.When the rock slope slips caused by seismic load,the landslide failure mechanism caused by gravity load can be divided into slip-shear failure and medium slip-end fracture type.