Numerical study on the swelling and failure of red-layer mudstone subgrade caused by humidity diffusion

Red-layer mudstone is a typical soft rock with low strength, easy weathering and disintegration, and significant swelling. This is an important reason for the swelling, deformation, and failure of red-layer mudstone subgrades. In this study, a humidity diffusion–deformation–fracture coupling model based on the finite discrete element method (FDEM) is used to simulate the process of moisture absorption swelling deformation and failure of the red-layer mudstone subgrade. First, two examples with analytical solutions are used to verify the accuracy of the model in addressing the humidity diffusion and swelling stress problems. Subsequently, the influence of multiple factors on the moisture absorption swelling deformation and failure of the red-layer mudstone subgrade is simulated. The results show that shear cracks mainly occur during the moisture absorption swelling of the red-layer mudstone. With an increase in the number of crack zones, the swelling coefficient and initial moisture content of the crack zones, average swelling deformation, and total number of cracks on the mudstone subgrade surface increased. Simultaneously, the fluctuation of the swelling deformation of the subgrade surface is positively correlated with the average moisture content and total number of cracks in the mudstone layer. In addition, the degree of influence of these factors on the swelling deformation and failure of the red-layer subgrade is also discussed. The numerical calculation results are conducive to a better understanding of the mechanism of moisture absorption swelling and failure of red-layer mudstone subgrades.