Numerical Evaluation of Suction Effects and Groundwater Table Variations on Long-Term Pavement Subgrade Performance

Over the past few decades, flexible pavements across the globe have seen a significant reduction in their service life due to climate changes. The flexible pavements with unsaturated subgrades undergo volumetric changes during the drying and wetting phases, affecting their long-term deformation behavior. These phases cause significant variations in matric suction and groundwater table depth. This study employs a coupled pore pressure-deformation analysis on flexible pavements to investigate the impact of groundwater table depth and suction variations in unsaturated subgrades. Finite-element simulations using the Abaqus and developed USDFLD code were validated against literature data. Sensitivity analysis was conducted by varying the suctions in subgrades during drying and subsequent wetting to evaluate the groundwater table depth. Furthermore, under heavy cyclic wheel loading, pavement-deformation analysis was conducted to investigate the influence of subgrade suction. The findings demonstrate that, after an initial drying phase at 5000 kPa suction, wetting over 180 days caused the groundwater level to rise from 5.45 m beneath the subgrade to the surface. This led to a 98% increase in surface-vertical deformations due to cyclic wheel loading after 180 days of wetting compared to the deformations during the drying phase at the same suction level. This assessment of groundwater-depth variations and long-term deformation behavior with the impact of suction improves the design and sustainability of flexible pavements.