Experimental Study On Shear Mechanical Properties Of Rock Joint Under The CNS Conditions

Engineering rock masses usually contain a large number of joints,these joints occurrence affecting the integrity of the rock mass,reducing the strength of the rock mass.The mechanical properties of joints affect the mechanical properties of rock masses to a certain extent,and then affect the safety and stability of engineering rock masses.For deeper underground engineering,during the shearing process of rock joints,confining pressure limits the free dilatancy of the jointed rock mass,which conforms to the CNS boundary conditions.This article uses RDS-200 shear test system.Using the threedimensional parameters of structural planes and the characteristics of acoustic emission test parameters,the shear mechanical properties of sandstone and granite joints under constant normal stress(CNL)and constant normal stiffness(CNS)boundary conditions are experimentally studied.Analyze the relationship between the shear stress,shear displacement,normal stress,normal displacement and other parameters of the two rock joints in the shearing process.Research indicates:Under the same initial normal stress,the peak shear stresses of sandstone and granite joints under CNS boundary conditions are both greater than under constant normal stress(CNL)boundary conditions.The CNS boundary condition improves the shear strength of the rock.Under CNL boundary conditions,residual shear strength manifests as stress softening.Under CNS boundary conditions,the normal stresses of sandstone and granite both increase with the increase of shear displacement and the greater the normal stiffness,the greater the increase in normal stress,and the rock joints show the phenomenon of first dilation and then shrinkage with the increase of shear displacement.Under CNS boundary conditions,the increase in peak shear strength of sandstone and granite increases with the increase in normal stiffness and increases as the initial normal stress increases.CNL and CNS under boundary conditions,the acoustic emission characteristics of rock joints during shearing show that: The acoustic emission energy of sandstone and granite,acoustic emission ringing count,acoustic emission duration,acoustic emission effective voltage,and acoustic emission peak frequency are basically positively correlated.When the peak shear displacement occurs,the acoustic emission of rock joints has the characteristics of maximum energy,long duration,large ringing count,and large amplitude.These acoustic emission parameters can be used to judge whether the rock joint reaches the shear peak.Under CNS boundary conditions and the initial normal stress is the same,as the normal stiffness increases,the acoustic emission energy and ringing count of sandstone and granite also increase.The research results are of great significance to the evaluation of deformation and failure of deep rock mass engineering.66 pictures,10tables,75 references.