Hydromechanical behavior of unsaturated sandy soils with different particle shapes under loading–unloading paths: Numerical simulation and experimental validation

This study investigates the simultaneous influence of particle shape and initial suction on the hydromechanical behavior of unsaturated sandy soils. Anisotropic loading–unloading tests at constant water content conditions were conducted on three sands with distinct shapes (Firoozkooh – most angular, Babolsar – Subangular, and Mesr – roundest) using a direct shear apparatus. Particle shapes were quantified in terms of sphericity, roundness, and regularity using the results of scanning electron microscopy (SEM) tests. In addition, a coupled hydromechanical model based on elasto-viscoplasticity was developed and validated against the experimental results first. The model was then employed to conduct a parametric study (compressibility, pore water pressure, and permeability) with an emphasis on the role of particle morphology and shape. The findings revealed rounder particles (higher regularity) experienced higher volumetric strain (${\epsilon }_v$) under lower suction but less ${\epsilon }_v$ with increasing suction compared to angular sands. Moreover, the rate of permeability reduction during loading in Mesr sand was 1.5 times and 2.4 times higher than that of Babolsar and Firoozkooh sands at near-saturation condition. However, this amount decreased with increasing suction. Pore water pressure (PWP) generation was highest in the most angular sand due to its retention characteristics. The relationship between void ratio and PWP was independent of loading cycles and exhibited a linear dependence. Particle shape significantly impacted this relationship, with rounder sands showing a higher rate of void ratio change per unit change in PWP.