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 vwith 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.

The study examines the effects of pressmud (PM), an innovative, sustainable, and beneficial alternative for soil treatment, on the hydromechanical behaviors of sand-bentonite (SB) through a series of laboratory tests, including unconfined compressive strength (UCS), free swelling, and 1D consolidation. SB mixtures with 10 and 15% bentonite (by sand weight) and PM at 4, 8, and 12% (by SB weight) were evaluated. Additionally, microstructural analyses using X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to elucidate the mechanisms of soil improvement. The results indicate that PM incorporation reduces the maximum dry unit weight while significantly enhancing the UCS of SB mixtures, with maximum strength increases of 111.5 and 65.5% observed in mixtures containing 10 and 15% bentonite, respectively, after 28 days of curing. These changes help not only enhance the strength properties but also decrease the self-loading on the landfill liner. Moreover, higher PM contents exhibit a dual impact of reducing swelling strain while slightly increasing both compressibility and permeability. Despite the marginal increase in permeability, it still meets the necessary criteria for serving as a landfill liner (< 10(-7) cm s(-1)). The observed effects of PM on SB behavior can be ascribed to the synergistic effects of natural fibers and cementitious gels, as confirmed by microstructural analyses. The natural fibers mainly contribute to the shear resistance of the interface, while the cementitious gels bridge and interlock the solid particles, thereby enhancing the hydromechanical performance of SB. It is concluded that the reuse of PM in soil stabilization not only enhances the hydromechanical performance of SB but also results in better PM management.