Engineers have limited control over the process of soil formation, which can pose challenges when it comes to constructing structures such as dams, pavements, rail tracks, and foundations. To address this issue, a study was conducted to examine the mechanical properties of Hormoz Carbonate Sand and Firoozkooh Quartz Sand No 161. The goal was to predict the settlement, particle breakage, and shear strength of these sands. Tall oedometer and direct shear tests were conducted in a drained condition and the samples were prepared with the dry pluviation method in two different relative densities (30% as loose and 80% as dense) and consolidated under various confining pressures. The results revealed that in dense specimens, the particle breakage index increased as the porosity decreased. In the tall oedometer tests, it was observed that the vertical applied stress decreased with increasing height of the soil sample. Additionally, particle breakage decreased with depth in the samples, corresponding to the decreasing vertical applied stress. Furthermore, direct shear tests were performed on soil samples of different heights (0.5, 1, 1.5, 2, and 3 cm) using a direct shear apparatus. It was found that in the lower sample heights (0.5, 1, 1.5 cm), a greater amount of breakage occurred due to a higher percentage of soil volume placed in the shear zone. The results also indicated that increasing the shearing rate led to a reduction in the particle breakage index.

Fine-grained sand deposits in subtropical regions are valued for their low settlement percentages, providing high load-bearing capacity for foundations. Despite existing literature, certain behaviors of these deposits, particularly under cyclic loading in unsaturated conditions with stiffness control, still need to be better understood. Given the potential for shaft friction degradation in cyclically loaded axial piles, this gap is critical. This paper comprehensively investigates the mechanical properties of PE-Sand from a Southern Brazil deposit under cyclic loads, integrating laboratory and field analyses. Characterization involved granulometric, specific gravity, consolidation, matric suction, microscopic, mineralogical, and chemical tests. Uncommon unsaturated direct shear tests were performed, evaluating shear interface degradation under one-way and two-way cyclic loads. Standard penetration and seismic piezocone tests at 25m depth contrasted field properties. Findings identified uniform micaceous quartz sand. A novel conceptual model for PE-sand cohesion emerged from stiff-direct shear tests. Cyclic tests revealed heightened interface degradation with fewer cycles at increased load amplitudes. Fatigue results converged to a cumulative damage value, signifying material criticality limiting sand-sand interface resistance. Field exploration confirmed a heterogeneous sand deposit with geotechnical properties akin to laboratory findings. This study contributes nuanced insights into fine sand behavior under cyclic loading in unsaturated conditions, bridging gaps in existing knowledge.