Study On Shear Strength And Constitutive Relation Of Protruding Loess

The joint shear strength characteristics of loess had important effect on the stability of the joint engineering,and the joint shear strength is closely related to the joint surface morphology.Therefore,joint surface morphology was studied.First of all,on the basis of field investigation and selection of suitable field collected natural loess joint specimens,using profilograph is used for measuring joint surface morphology,then we draw the joint plane two-dimensional contour curve.Joint surface characteristic parameters were calculated by using statistical methods,and then RMS z1 slope,peak point density eta and RMS z2 three parameters are selected for the method of fuzzy mathematics comprehensive,which evaluate joint surface morphology.According to the result of statistic data and the experience,the scope of the single factor classification is determined.Finally the surface morphology RJ and the result of classification is got from the integrated characteristic parameters of natural loess joint specimen.Based on the joint surface morphology classification standard,sample is preparated,then moisture content of the loess joint shear strength parameters is syudied by using indoor small direct shear test method,and compared the lab large-scale direct shear test with small direct shear test results,the influence of size effect on the shear strength is studied.According to the results of all tests,the joint characteristics of shear stress and displacement curve is studied.Joint surface morphology study found that different space between the joint surface morphology of natural loess soil sample is different,the same venue,joint surface morphology;The scope of the joint surfaces kurtosis coefficient K value is 2 ~ 3,the average is close to 3,all show that the joint surface coordinates height distribution is gaussian distribution or quasi gaussian distribution;Verify found RJ and joint shear strength has a good linear correlation,shows that this method has the feasibility of joint surface cla ssification.The direct shear test results show that the loess joint shear strength accord with Moore-coulomb criterion,and the cohesive force is so small that could be neglected;Loess joint Angle of internal friction peak changes small with the increase of water content at first,when the water content is greater than a certain value,the peak Angle of internal friction decrease amplitude change.The relationship of strength between the water content could be described by index available form,and shows the calculating formula of joint shear strength,which is verified.Loess joint has size effect,and direct shear test is mainly affects sample size’s contribution to the shear strength of joint surface fluctuation degree.The greater the size is,the greater shear strength is.Loess joint shear stress and displacement curve belongs to no peak strain hardening type curve,and then a reasonable constitutive model is put forward;Fitting test results using by the proposed constitutive model gets the initial shear stiffness.The results found that the initial shear stiffness reduced with the increase of water content and the initial shear stiffness increases linearly with the normal stress increases.