A coupled hygro-mechanical model for moisture diffusion and curling mechanism in saturated and unsaturated soil using ordinary state-based peridynamics

Soil curling, a natural phenomenon in thin soil fragments induced by desiccation cracks, exacerbates the potential threats of soil cracking. Analyzing soil curling, especially in conjunction with soil desiccation cracking, poses challenges in existing numerical investigations due to factors such as inadequate knowledge of the soil curling mechanism, complex soil characteristics with diverse parameters, moving boundary conditions during deformation, and crack initiation and growth. This study aims to uncover the soil curling mechanism using a fully coupled hygro-mechanical ordinary state-based peridynamic (OSB PD) model and its corresponding monolithic solutions. Specifically, the PD form of the moisture diffusion equations for saturated and unsaturated states are derived by employing the variational principle with nonconservative Lagrangian action and peridynamic differential operator (PDDO). Also, the PD bond force is derived by considering the energy equivalent principle for a fully coupled hygro-mechanical model. A model of soil strip desiccation deformation and curling is constructed while considering realistic moving boundaries of moisture and displacement with relevant parameters, and soil characteristics evolution from saturated to unsaturated states. It successfully captures the entire curling process, including concave-up and concave-down curling. Furthermore, this study explores the influencing factors of liquid limit, extra evaporation surface, and thickness on the curling performance.