Study Of The Effect Of Joint Mismatching On Its Normal Deformation

Natural joint can be the combination of two joint walls that are touching.Under normal stress,the joint engenders normal deformation and the size,distribution,and linking status of its internal contact area and pore area also change,which affect the mechanical,acoustic and permeation characteristics of the joint.The existing research shows that the joint normal deformation is related to the roughness,the mismatching and the wall strength of the joint.At present,many scholars have carried out a lot of qualitative and quantitative studies on the roughness and wall strength of joints,but the study of joint compliance is still in the qualitative stage.Therefore,it is of important theoretical and practical significance to study the influence of the mismatching on the normal deformation of rough joints.In this paper,I obtained the artificial rough joint through the laboratory experiments(direct shear test,Brazil split test,direct tension test),random function and composite topography,and I analyzed the feasibility and applicability of the three methods by 3D laser scanning,3D printing technology and test analysis.I determined quantitative method of the joint mismatching coefficient by the digital image technology,and I based the quantitative analysis of the effect of mismatching on artificial roughness joints(gesso,mortar)on this method by normal cyclic loading test.The main conclusions are as follows:(1)The three-dimensional joint model with different roughness can be obtained by direct shear test,Brazil split test and direct tension test.The roughness of joint model obtained by direct shear test has little difference with that obtained by Brazil splitting test on the same rock,while the joint model obtained by direct tensile test has the highest roughness.The roughness of the granite joint(coarse particle)is higher than that of sandstone joint(coarse particle)in the same type of test(particle is finer than the former),Especially in the direct tensile test.The joint model obtained by the same rock and laboratory test has a relatively fixed roughness,which changes in a very small range.The above characteristics are related to the force failure characteristics of various laboratory tests and the particle size of samples.(2)Using random function to generate a joint digital model-3D printing rough joint bottom die-casting method to obtain joint samples,which can not only overcome the mechanical processing of rough joint mould defects(processing difficult and costly),but also can avoid the limit of current 3D printing joint sample high price.The results of morphological scanning show that the repeatability of the joint parallel sample obtained by this method is higher,and the difference between the roughness joints and the corresponding digital joint model is smaller.(3)The joint model of composite topography can transform the problem of two rough surface into the problem of one rough surface ang a plane surface,it can simplify the model and reduce the workload of theoretical research to a certain extent.For the joint closure characteristics,the model can be used to study the joint closure characteristics without joint local failure,but the method of composite topography will change the stress distribution in the joint and cause the local stress concentration and the failure of the test specimen at less stress.(4)The coincidence coefficient JMC of the two-dimensional joint model can be quantitatively measured by digital image technology.Different mismatching joints can be obtained by dislocation of upper and lower joints.But with the increase of displacement,the joint mismatching coefficient(JMC)is not simply increasing or decreasing.Therefore,it is not rigorous enough to distinguish the joint mismatching coefficient by displacement.(5)With the increase of the joint mismatching coefficient of Gesso and mortar joints which have same joint roughness coefficient,the maximum deformation decreases in power function,the initial normal stiffness increases in linear function,aperture decreases in linear function.(6)With the increase of the joint roughness coefficient of gesso and mortar joints which have same joint mismatching coefficient,the maximum deformation decreases in linear function,the initial normal stiffness increases in linear function,aperture decreases in linear function.(7)The normal deformation curve of gesso and mortar joints satisfies the BB model,in which the maximum normal deformation,the initial normal stiffness and joint aperture of joints are related to the joint mismatching coefficient(JMC)and the joint roughness coefficient(JRC).Based on the experimental results,an empirical formula for joint deformation parameters(joint maximum normal deformation and initial stiffness and aperture)expressed by JMC and JRC is obtained.A joint normal deformation BB model including JMC and JRC has been successfully established.