Experimental Study On Creep Characteristics Of Marble Joints With Graded Shear

Joints are widely distributed in rock mass engineering,which control the mechanical properties and mechanical functions of rock mass,and have a certain influence on the safety and stability of rock mass engineering.And the shear rheological properties of joints,as one of the important influencing factors of the mechanical properties of joints,are the important reason for the deformation and instability of the surrounding rock in geotechnical engineering.In this paper,rock joints are studied by direct shear tests,shear creep tests under tangential graded loading,shear creep tests of normal graded unloading and tangential graded loading-creep-unloading tests.The deformation and energy change characteristics of joints under several different shear stress paths are analyzed and the shear failure mechanism is expounded around the failure patterns of joints.And some signs of instability before failure are summarized.The main conclusions are as follows:(1)Joint in hierarchical load shear creep test,the instantaneous shear displacement and shear stress level was positively than the isochronous curve method is used to determine the joint shear strength of its long-term creep shear strength ratio and the scope of direct shear strength ratio is 72.34%~83.84% and 61.92%~83.84% respectively joint contour convex wear associated with normal stress and shear stress,normal stress and shear stress,the greater the joint Burgers was not wear the more severe the improved model can better reflect the joints under different shear stress shear creep deformation law(2)Method to uninstall sizing shear creep test under the first normal stress level of the tangential creep curve attenuation-steady state characteristics of the most obvious method to the sudden sharp increase,the creep displacement is joint acceleration creep shear slip failure precursor method to stress on the shear creep deformation has a certain influence,by adopting the method of transient stress than coulomb criterion method to get the equivalent joint strength parameters of small Burgers was not considered method to improve stress model can better reflect the joint method to load shedding shear creep elastoplastic characteristics.(3)Graded cyclic shear loading-creep-unloading experiment,considering the influence of the method to the load on the joint energy dissipation,the total deformation and elastic deformation energy along with the normal stress and the increase of cycling times increases,and the relationship between cycles exponentially hysteresis ring area is positively correlated with cycles,normal stress is less than 6.5 MPa and greater than 7.8 MPa,the hysteresis loop back area and cycling times is linear and exponential relationship respectively.(4)The offshoring of the grading cyclic shearing test curve can be divided into the accelerated ascending segment,the uniform increase segment and the uniform descending section.The increase rate of the cumulative tangential plastic deformation decreases with the increase of cycle times.Shear can add unloading curve by a shear sliding section is divided into two curve appears after the period of cyclic loading at all levels or creep cumulative normal displacement is lower than the previous cycle,both can be a long-term forecast joint shear buckling loading or unloading process always normal displacement curve in the previous cycle method before or from the previous cycle to the displacement method to cross displacement curve,can be used as a joint shear instability of recent omen.