Generalized Plastic Mechanics–Based Constitutive Model for Estimation of Dynamic Stresses in Unsaturated Subgrade Soils

Abstract

This paper presents a generalized plastic mechanics–based constitutive model for the estimation of dynamic stresses in unsaturated subgrade soils under repeated vehicle loading conditions. The stresses in subgrade soils are taken as the sum of two components: dynamic stress and total suction. The increment of dynamic stress consists of three subcomponents, including coaxial stress increment, stress increment due to rotations of principal stresses under vehicle loading, and stress increment due to stress accumulation under repeated loading. The total suction in unsaturated subgrade soils is considered to comprise two subcomponents: wet suction characterizing the capillary effect between liquid and solid phases; and structure suction quantifying the adsorptive and bonding effects between soil particles. The proposed dynamic model is then solved using the numerical nonlinear incremental calculation method. A case study is presented in the end to elaborate on the application of the proposed model in practice. The calculated stresses in subgrade soils using both the proposed model and the conventional equivalent static load model are compared against the measured values in the field. Through the case study, the advantages and the practical value of the proposed model are demonstrated.