Investigation of the creep behavior and time-dependent constitutive model of red-stratum mudstone fill material in high-fill subgrade

To effectively predict and mitigate geotechnical engineering disasters resulting from the utilization of redstratum mudstone as fill material in high-fill subgrade construction, an in-depth investigation of its creep behavior is essential. In this study, the effects of water content and initial void ratio on the creep behavior of redstratum mudstone fill material were investigated through a series of scanning electron microscopy (SEM) tests and one-dimensional creep tests. A fractional-order element model and a novel elastic-viscoplastic (EVP) model considering the effect of particle breakage were proposed. The results indicate that upon water immersion, the red-stratum mudstone particles exhibit a rough honeycomb surface with a loose and irregular pore structure, increased microporosity and microcracks, leading to reduced particle strength. The creep process of red-stratum mudstone fill material can be divided into three stages, and the magnitude and rate of creep deformation are positively correlated with the vertical stress. Higher initial void ratios and water contents result in greater creep displacement and longer times to reach steady-state creep. The isochronous stress-strain behavior transitions from nonlinear to linear, reflecting the irreversible deformation mechanisms of particle sliding and breakage, which lead to continuous elastic-viscoplastic deformation of the red-stratum mudstone fill material. A fractionalorder element model was proposed, which has a significantly better fitting effect than the classical Burgers model. Furthermore, based on the one-dimensional elastic-viscoplastic (EVP) model, considering the influence of initial void ratio and water content on the secondary consolidation coefficient (phi), and introducing particle breakage and stress-related compression parameter (lambda), a novel EVP model was developed. Comparative analysis and validation test data confirm that both the fractional-order element model and the novel EVP model can accurately describe the creep behavior of red-stratum mudstone fill material.