ELASTO-VISCOPLASTIC CONSTITUTIVE MODEL OF SANDY SOIL CONSIDERING STRESS PATH AND LOADING RATE

Based on the experimental results of drained plane strain compression(PSC) on saturated dense sandy soil along a wide variety of stress paths,the effects of stress path and loading rate on the deformation and strength characteristics of sandy soil are investigated. It is found that the irreversible shear strain and irreversible volumetric strain are dependent on stress history and stress path. And significant loading rate effect is observed in the tests. The same as creep deformation and stress relaxation,loading rate effect should be attributed to the viscous properties of the sandy soil specimens. One of the most important characteristics of loading rate effect is the stress changes sharply with a very high stiffness,nearly elastic behavior,when the strain rate suddenly changes.Subsequently,the use of any quantity shown above as the hardening parameter is not well reasonable in the traditional plastic theory. Based on the analysis of these test results,a novel modified irreversible strain energy, Wir,and the related function are shown to be stress path-independent. An energy-based elasto-viscoplastic constitutive model of sandy soil,described in a nonlinear three-component framework,is proposed with the use of Wir as the hardening parameter. The presented model can take into account the effects of stress path,pressure level,inherent anisotropy,void ratio,work softening associated with strain localization into a shear band and loading rate effect on the stress-stain behavior. The finite element method code incorporating the presented model is validated by simulating the PSC tests. It is shown that the proposed model can much better simulate the effects of stress path and loading rate on the deformation and strength characteristics of sandy soil than the previous models.