Experimental Study On The Shear-Seepage Coupling Characteristics Of Joints Under Different Filling Materials

Joint is the weak plane in natural rock mass.Generally,there are two types of joints based on the origin of the filling material,which results from continuous weathering of joint surface,and the in-situ deposition of ground surface material from the nearby area.Both the strength and engineering stability of rock mass and the seepage characteristics of joint are affected by the properties of filling material.Therefore,it's useful to study the shear-seepage characteristics of joint filled with different filling materials for evaluation of the stability of rock mass.In this paper,based on the self-developed coal-rock shear-seepage coupling test device,a series of shear-seepage coupling tests under constant normal stress was performed on the joints made of rock-like material.The 3D optical scanning technology was employed to collect the point cloud data of the joint topography.Then,the characteristics of strength,deformation,seepage and morphology of joints was analyzed under different filling materials,filling particle sizes and water pressure.Based on the evolution of joint aperture,the force distribution and shear-seepage coupling mechanism of joint were also discussed.The results show that:(1)The peak shear stress and normal displacement of joints decreases as filling material varies from gypsum,debris to clay,which contribute greatly to the properties of joints.Unfilled joints have obvious abrasion and JRC decreases the most,followed by the joints filled with gypsum and debris while JRC remains nearly the same for clay.The materials failure and joints surface abrasion are mainly controlled by the aperture evolution and local stress concentration.In the area aperture decreases,stress concentrate and joints and filling materials break easily there.(2)The bigger the filling particle size is,the greater its crushability and compressibility will be.Resulting from this,the peak shear stress and normal displacement of joints decrease,and the dilatancy effect becomes subtle.(3)As the water pressure increases,the peak shear stress and normal displacement of joint decrease,and the flow rate increases.Joints filled with debris and clay are more sensitive to the changes of water pressure than those filled with gypsum.The peak flow rate of joints filled with different materials is closer under a larger water pressure.(4)Coupling interaction exists between joint and fluid.Joint affects the seepage characteristics mainly through aperture evolution and aperture development of filling materials.Fluid can weaken the mechanical properties of joint through softening and erosion.In the shear-seepage process,the fluid pressure can promote the development of cracks in the filling materials,and in turn,the expansion of the seepage channel will accelerate the softening impact on filling materials.