Triple-Shear Unified Elasto-plasticity Constitutive Models For Unsaturated Clay Based On Coordinate Translation Method In Normal Consolidation States And Secondary Development Of ABAQUS Subroutine

Triple-shear unified yield criterion of unsaturated soil as the failure criterion can reflect the change of the stress state,and the influence of matrix suction.This paper uses the failure criterion by coordinate translation method building the triple-shear unified constitutive model of unsaturated soil of single stress variable method and the triple-shear unified constitutive model of unsaturated soil of double stress variable method.The two models can reflect the change of stress state and consider the influence of matrix suction.In addition,there is no triple-shear unified constitutive model of unsaturated soil in ABAQUS finite element analysis software material library.This paper will develop UMAT subroutine on the platform of secondary development of ABAQUS by triple-shear unified constitutive model of unsaturated soil,and finally will establish three-dimensional gravity retaining wall model and apply the subroutine to the gravity retaining wall model.The ABAQUS material library is also an extension.The main contents of this paper are as follows:1.The coordinate translation method is used to deduce the triple-shear unified constitutive model of unsaturated soil of single stress variable method and the triple-shear unified constitutive model of unsaturated soil of double stress variable method.The two models can reflect the change of stress state and consider the influence of matrix suction and make the mechanical properties of unsaturated soil more consistent.Finally,the corresponding elastoplastic stiffness matrix is derived based on the constitutive model,which also provides theoretical basis for the writing of UMAT subroutine.2.The second development of ABAQUS finite element analysis software and UMAT subroutine are briefly introduced.In this paper,triple-shear unified constitutive model of unsaturated soil is compiled into a UMAT subroutine by a display integral algorithm.3.The remolded soil in NanChang area is taken as the experimental sample,and the GDS triaxial test of unsaturated soil is conducted under different confining pressures and the different matric suction s(0kPa,20kPa,50kPa,80kPa),respectively.The direct shear experiments were performed under the matric suction s(0kPa,100kPa,200kPa,300kPa,400kPa)and different confining pressures.By comparing the compiled UMAT subroutines of the single stress method and the UMAT subroutines of the double stress method with the results of the true triaxial numerical model,the correctness of the subroutines is verified Furthermore,the true triaxial simulation under single stress variable and true triaxial simulation under double stress variable are further analyzed.It is concluded that with the increase of the influence coefficient b of the intermediate principal stress,the shear stress and volume strain under single stress variable and double stress variable will also increase.When the axial strain is constant,the greater the matric suction is,the greater the shear stress is.When the axial strain is constant,the greater the matric suction is,the smaller the volume strain is.Compared with the method of single stress variable,when matric suction and the influence coefficient of intermediate principal stress and axial strain are constant,the shear stress under double stress variable is larger than that under single stress variable,and the volumetric strain under double stress variable is larger than that under single stress variable.The experimental value of the triaxial test of unsaturated soil is compared with the simulated value of the UMAT subroutine of the single stress variable method and the simulated value of the UMAT subroutine of the double stress variable method.The data show that the simulated values of the single stress variable method and the simulated values of the double stress variable method are roughly the same as the experimental values,which can reflect the strain hardening characteristics of the soil.In confining pressure is larger,the test value is generally greater than the simulation under the single stress variable and double stress variable values,and other conditions must,under the single stress variable and double stress variable simulation value increases with the increase of matrix suction,when the matrix suction of the larger,simulation under the single stress variable and double stress variable values,using the equivalent substitution method and coordinate translation method vary with the test results are large,but the overall trend is same.Reflection UMAT subroutine can reflect the characteristics of unsaturated soil.4.Finally,the paper sets up the 3 d model of gravity retaining wall engineering case of a 3 meters high,1 meter wide in the finite element software ABAQUS to,and compiled UMAT subroutine is applied in the model and to analyze the stress distribution of gravity retaining wall and horizontal and vertical displacement of the soil of that the intermediate principal stress b is 0,0.25,0.5,0.75,1 and the matrix suction s 20kpa,50kpa,80kpa respectively.The intermediate principal stress b of 1,the matrix suction of 20 kpa,50 kpa,respectively 80 kpa under the single stress variable and double stress variable model of displacement distribution were compared The results show that the soil displacement behind the wall decreases gradually due to the increase of the influence coefficient b of the intermediate principal stress.As the matric suction s increases,the displacement also decreases.Single stress variable and double stress variable method the results of the horizontal comparison,the results show that the double stress variable method in the matrix suction and the intermediate principal stress effect coefficient certain cases,the displacement of soil under the double stress variable method is more smaller,it also reflects the intermediate principal stress coefficient b,the greater the soil strength has increased gradually,the soil characteristics are better;The larger the matric suction,the greater the shear strength and the smaller the soil displacement.Compared with the single stress variable method,the soil mass under the dual stress variable method is more stable.It is consistent with the theoretical analysis results.