Experimental Study On The Shear Strength Weakeningof Rock Joint Surface

In this paper,cement mortars were used as similar model materials to make four joint specimens with different fluctuation angles,and the joint shear tests were carried out under five different normal stresses.By analyzing the shear stress-shear displacement curve obtained from the test,the shear failure mechanism of the joint surface is found,and the shear strength of the joint surface and the residual strength after weakening are quantitatively analyzed toknow the weakened process and mechanism.The normal displacement-shear displacement curve obtained from the test was analyzed to obtain the dilatancy and expansion characteristics of the joint surface during the test.According to the research done in this paper,the following conclusions are drawn.(1)Analyze the failure mode and shear strength-shear displacement curve of the test,and separate the two failure modes that are influenced by the fluctuation angle and the normal stress.The linear fitting analysis of the shear strength and residual strength is carried out,and the influence of the variation of the undulation angle on the shear strength is greater than that on the residual strength.The ratio of the peak shear strength to the residual strength is used as the index of the weakening of the strength,and the influence of the undulation angle on it is obtained.Coulomb-Mohr criteria were compared for the fitting formulas at two strengths,and the variation of equivalent cohesion and equivalent internal friction angle in the weakening process was obtained.(2)Based on the normal displacement-shear displacement curve of the test,it is divided into three stages of shearing,expansion and dilatancy.The characteristic values of each stage are analyzed to get the influence of the rate of dilatancy deformation by the normal stress and undulation angle.The expression of the dilatancy curve in the logarithmic function form for the stage of dilatancy is summarized,and the corresponding dilatancy angle is obtained.(3)The ratio of shear stress to normal stress is the friction resistance coefficient.According to the JRC-JCS shear strength model formula,the friction resistance coefficient model is proposed.Then the expression of shear stiffness with respect to normal stress is obtained from the incremental shear stress equation,and the corresponding expression of shear displacement is obtained.The shearing process of the joint surface is quantified.Thus the model values and experimental values are obtained,and it is found that the two have good matching.