Humidity field for unsaturated subgrade accounting for the hydro-mechanical coupling and the difference of compactness: A simulation method

Abstract

The safety and stability of road structures heavily rely on the precise assessment of subgrade humidity. However, existing methods often fall short in fully considering the coupling effect between humidity and stress states, as well as variations in compactness across different subgrade areas. In this study, a new model is proposed for simulating water migration in soil subgrade, incorporating hydro-mechanical coupling and the degree of compaction. The model is implemented using a newly added physical field in the COMSOL Multiphysics platform, and a numerical method is developed for calculating subgrade humidity. Moisture migration behavior in subgrades is investigated by selecting two atmospheric environments, namely dry and wet conditions. The results demonstrate that the developed humidity calculation method, accounting for hydro-mechanical coupling and compactness variations, yields reasonable and accurate predictions. Substantial differences in subgrade humidity are observed between wet and dry conditions. Compared to the dry conditions, pronounced fluctuations in subgrade humidity are observed in areas near slopes, with the equilibrium moisture content increasing by approximately 50% compared to the initial content. Additionally, the equilibrium time for moisture migration is significantly shortened under wet conditions. Based on these findings, it is recommended that waterproof should be considered in subgrades exposed to wet atmospheric environments to avoid excessive moisture content in subgrade.