Experimental Study On The Strength Weakening Mechanism Of Rock Joint Surface

The engineering jointed rock mass is constantly subjected to repeated loads during the long geological process.The weakening of the joint surface strength is quite common.In this paper,artificially poured concrete is used to make specimens with different relief angles.Direct shear tests and cyclic loading and unloading direct shear tests are carried out under different normal stresses.According to the shear test process and test curve,the characteristics of joint shear stress shear displacement,normal displacement shear displacement curve and joint failure mechanism are analyzed.This paper systematically studies the mechanical properties of joint shear weakening strength and deformation.This paper quantifies the weakening parameters of joint strength and the evolution of shear displacement.The main content and results of this paper are as follows:(1)Based on the experimental shear stress-shear displacement curves,the normal stress,the angle of undulation,and the friction coefficient model(?/?)and joint strength weakening characteristics of joint specimens were studied.The least-squares linear and parabolic regression fittings of the peak strength and residual strength of the joint shear weakening stage were respectively analyzed,and it was concluded that the peak strength and residual strength were more suitable for the Mohr-Coulomb strength criterion.The joint failure modes were analyzed under different loading conditions.The results showed that the development of joint shear failure mode and post-peak weakening stage was controlled by the size of the undulation angle and the magnitude of normal stress.(2)According to the shear dilatancy curve,the evolution of the shear dilatancy deformation and the dilatancy angle in the peak area of the joint is analyzed.On the basis of the empirical shear expansion model,the residual shear bulging angle model is established for the peak dilatancy angle fitting analysis of different undulating angles.(3)Based on Mohr-Coulumb's theoretical model of strength,taking into account the effects of shear weakening,a residual strength formula related to normal stress is proposed.The shear deformation characteristics of joints are analyzed,and it is concluded that the shear stiffness will have a corresponding deteriorating effect when the joint strength is weakened.Based on the idea of the hyperbolic model proposed by Clough,the relationship between the shear stress and the shear displacement after joint strength weakening is obtained by mathematical geometry method.(4)For the strength weakening of joints,the weakening of joint peak strength to the residual strength is decomposed into a series of deformation processes of brittle drop and plastic flow.It simulates the weakening process of joint strength.The results is well agree with the experimental datas.