ELASTOPLASTIC CONSTITUTIVE MODEL AND MECHANICAL BEHAVIOR OF UNSATURATED LOESS

To address the issue of the absence of a suitable loess constitutive model in the study of seismic response in loess tunnels, the elastoplastic constitutive model of unsaturated loess was established by replacing the fixed yield surface with the yield surface (i.e., the variable loading surface). This model improves the algorithm of integration since the shape and position change in the stress space due to the continuous loading of unsaturated loess after yielding. In this study, the elastoplastic constitutive model was used in isotropic compression, drained triaxial compression, and undrained triaxial compression tests. The test results were compared with the Cambridge model. The results revealed that the elastoplastic constitutive model achieved a smooth transition between elasticity and plasticity and can effectively simulate soil behavior. The numerical experiment of triaxial drainage compression conformed to the theoretical concept of the boundary surface model and provided ideal simulation properties. From the undrained dynamic triaxial compression numerical test, it was seen that the constitutive model can describe the elastoplastic deformation in the yield surface and better reflect the cyclic strength softening and cyclic stiffness degradation of soil.