This paper presents a straightforward approach for modelling volume change behavior of expansive soils during wetting–drying cycles. The swelling–shrinkage strain of expansive soils induced by cyclic wetting and drying was decomposed with distinctive physical background into a reversible component, which shows a synchronous change with the cyclic change of suction, and an irreversible component, which is generated mainly in the early stage of the wetting–drying process. The mechanisms of the two swelling–shrinkage strain components can be well explained through the double-level structure of expansive soils and its evolution with mechanical and hydraulic loading. The reversible component originates from the reversible deformation behavior of aggregates, and primarily depends on current suction or water content. The irreversible component is associated with the irreversible change of macrostructure, reflecting the difference in soil structures at current state and the equilibrium state. A practical constitutive model was proposed for compacted expansive clays from a global and phenomenological perspective. The model parameters can be calibrated with observed macroscopic deformation behavior without measuring microstructural parameters. The performance of the presented model was validated by simulating cyclic suction-controlled tests as well as an alternately soaked and dried test with irregular amplitudes of suctions.

Prediction of subsoil deformation under traffic loading requires honoring the dynamic nature of moving wheel loads and representing the stress path caused by such loads. A practical method in the framework of the layerwise summation procedure is proposed here for predicting the settlement of road overlaid on soft subsoil caused by traffic loading. The proposed method consists of a simplified approach for calculating the wheel load–induced stress and an empirical model for describing the accumulation of residual strain. Two amplification coefficients are introduced to account for the effect of moving speed on deviator stress and horizontal shear stress, respectively. The analytical solutions of the two amplification coefficients, which can be evaluated numerically, are deduced, and numerical results are presented in charts. Hence, the wheel load–induced stress in subsoil at different moving speeds can be calculated by multiplying the stress from a commonly used pseudostatic method with the values of the two amplification coefficients read from the charts. In addition, an empirical model is proposed for calculating the accumulation of residual strain in the subsoil under repeated heart-shaped stress cycles induced by traffic loading. The model is calibrated by simulating cyclic torsional shear tests of different clays. Providing the induced accumulated strain of the subsoil, the settlement of a road that results from traffic loading can be predicted by following the layerwise summation procedure. The performance of the proposed method is demonstrated by simulating the traffic loading–induced settlement of Saga Airport Road as an example.