A composite constitutive model for municipal solid waste considering multiple influencing factors

The stability of landfills poses a significant challenge to both environmental protection and safety, and the constitutive model of municipal solid waste (MSW) plays a crucial role in the nonlinear numerical analysis of landfill stability. This study proposes a composite constitutive model for MSW, which comprehensively considers the effects of fiber reinforcement, particle compression, mechanical creep, biodegradation, and dynamic loading. Based on a two-phase assumption, the model conceptualizes MSW as consisting of two phases: the basic phase and the fiber phase. The basic phase incorporates bounding-surface plasticity theory, considering the influences of particle compression, mechanical creep, biodegradation, and dynamic loading during specific volume evolution, boundary surface hardening, and the calculation of stress and strain. The fiber phase is modeled using an ideal elastic model to represent the fiber reinforcement effect. By constructing coupled equations, the two phases are successfully integrated into a unified constitutive model. Validation against triaxial test data from the literature demonstrates that the model’s predictions align well with experimental results. The model accurately simulates the upward curvature of the stress–strain curve and the continuous increase in volumetric strain under drainage conditions. Additionally, it effectively describes the increase in shear strength and pore water pressure, and the decrease in volumetric strain, under higher confining pressures. With increasing MSW age, the model predicts a significant increase in shear strength accompanied by a slight increase in volumetric strain. Furthermore, the model well captures the dynamic shear behavior of MSW under varying strain amplitudes and confining pressures. Finally, parameter analysis further explores the characteristics of the model.