Most existing constitutive models either cannot fully describe the mechanical properties of soils due to their simplicity,or cannot be applied easily due to their complexity and the difficulty of calibrating too many parameters.Based on the theories of nonlinear elasticity,elastoplasticity,modified Masing rules and the Singh-Mitchell creep model as well as the generalized Masing rules for 3D application,a simple,practical and unified elastoplastic-viscoplastic model considering the nonlinearity,cyclic hyste...