Elastic-viscoplastic model for structural clays based on a unified form of rational functions

Abstract:

To address the pronounced nonlinearity of stress-strain relationships during the compression deformation of structured clay and the limitations of traditional constitutive models in terms of mathematical rigidity and applicability, this study proposes an elasto-viscoplastic constitutive model for structured clays based on a unified rational function formalism. First, based on Maxwell elements, this study decomposed the total strain into the sum of elastic and viscoplastic strains, with a focus on investigating viscoplastic strain associated with structural effects. A rational function expression for viscoplastic strain-effective stress-equivalent time was established through one-dimensional compression behaviors. Second, under the assumption that “the viscoplastic strain rate of soil depends solely on effective stress and viscoplastic strain,” the viscoplastic strain rate expression for structured clay was derived by integrating the concept of equivalent time, and then a one-dimensional elasto-viscoplastic constitutive model for structured clay was derived. Third, the parameter calculation method was introduced, transforming the problem of solving parameters into a multiple linear regression task by using linear programming techniques, with matrix solutions implemented through computational tools. Finally, during model verification, the strain variation of soil under sudden loading conditions as a function of real time was derived. The model was applied to simulating conventional consolidation tests and creep tests, demonstrating its applicability and the feasibility of the parameter calculation method. The research results indicate that the proposed equivalent time model for structured clay effectively describes both the effective stress-viscoplastic strain relationship and the total strain-time relationship under one-dimensional compression.