| The tenso-shear coupling failure and compressive shear failure of soils are the main destroy modes of instability of slopes,such as soil slope,embankment,roadbed,refuse landfill,and so on.The slope instability is jointly influenced by tenso-shear coupling strength and compressive shear strength.Traditional studies on soil strength are mainly concerned with the soils subjected to the compressive shear stress state and can't describe the tenso-shear characteristics of soils.So far the strength model considering both the compressive shear strength and the tenso-shear strength has not been established.Therefore,it is of significance in theory and practice to research the tenso-shear and compressive-shear coupling strength of soils.Based on the existing studies,a tenso-shear and compressive-shear coupling strength model both under plane stress condition and under three-dimensional stress condition is developed,and its application on the instability of slope is researched.The main research work is as follow:(1)Based on the existing strength study,the mechanism of the tenso-shear and compressive-shear coupling strength is analyzed.A tenso-shear and compressive-shear coupling strength model of saturated clay is developed by discussing the strength characteristics of soils under the tenso-shear stress state and compressive shear stress state.Different types of saturated clay are selected for the uniaxial tensile test,direct shear test and triaxial shear test.It is shown that the proposed model performs very well.(2)The interactions between liquid phase and solid matrix in unsaturated clays can be divided into capillary effects and physicochemical effects according to their formation mechanism.Based on their different impacts on the soil strength,the corresponding ideal capillary strength formula and ideal adsorption strength formula are established respectively.Furthermore,a participation function is used to reflect the degrees of capillary effects and adsorption effects.A compressive shear strength model is thus developed.Comparing predicted results and exiting test results,it is shown that the proposed model can well describe the compressive-shear strength of unsaturated clays in wide suction range.Based on this compressive-shear strength model,A tenso-shear and compressive-shear coupling strength model of unsaturated clays is secondly developed.By comparison with the test results,the proposed tenso-shear and compressive-shear coupling strength model can well predict the tenso-shear strength and compressive-shear strength of unsaturated clay.(3)Through comprehensive consideration of tenso-shear coupling strength mechanism and the intermediate principle stress effect,the proposed tenso-shear and compressive-shear coupling strength model is extended to three-dimensional stress space.The corresponding failure function in ? plane and triaxial compression meridian plane are developed respectively,the nonlinear strength model in three-dimensional stress space is then proposed by means of linear transformation.By analysis of the predicted results and the experimental data of different types of soils,this three-dimensional nonlinear strength model can apply to different types of soils and well describe their tenso-shear and compressive-shear coupling strength under three-dimensional stress state.Furthermore,this model better reflect the intermediate principle stress effect.(4)Based on above three-dimensional nonlinear strength model,the secondary development of UMA.T is carried out by use of ABAQUS software.The UMAT procedure of constitutive relationship is coded using implicit backward Eular integral algorithm and its accuracy is verified by numerical experiments.This procedure is then applied to analysis of slope stability.Considering the reduction of parameters in tenso-shear and compressive-shear coupling strength model,the stability of unsaturated slopes under general condition,non-rainfall condition and rainfall condition are analyzed using strength reduction method.The results shows that the proposed model has much advantages in describing the deformation and failure mechanism of slope,the evolutionary development process of the equivalent plastic zone and thecritic slip surface,as well as the evaluation of slope stability. |
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