Molecular Dynamics Simulation and Lab‐Scale Experimental Testing of Water Migration in Unsaturated Expansive Clay

The mechanical performances of expansive clay in semi‐arid areas deteriorate with the change in humidity and temperature due to its characteristics of water‐swelling and drying shrinkage. So, investigating the moisture migration in expansive clays is of great significance. This study employs molecular dynamics (MD) simulations to elucidate microscale water transport mechanisms in clay mineral pores, complemented by experimental validation using a novel horizontal migration apparatus across temperature gradients (5°C, 20°C, 40°C). Quantitative analysis reveals that temperature significantly influenced water migration, with the migration rates at 5°C and 20°C accounting for approximately 30% to 60% of the rate observed at 40°C. Based on the MD simulation results obtained, a modified Kozeny–Carman equation is presented to simulate the hydraulic conductivity at various temperatures. The microscopic flow behavior of clay minerals was compared with the macroscopic characteristics of clay. The results demonstrate that hydraulic conductivity varies non‐linearly with changes in matric suction. Under the same matric suction, the computed hydraulic conductivity obtained from MD is higher than that of the experimental simulation. The arrangement and connectivity of soil pores at a higher suction have a more pronounced impact on soil permeability. These results elucidate the moisture migration mechanisms in unsaturated expansive clay at the microscale.