ركسانه زماني

The investigation of granular soil behavior under long-term cyclic loading, particularly in marine environments, plays a crucial role in the analysis an‎d design of offshore foundation systems. In this study, the effect of a large number of low-amplitude cyclic loadings on the mechanical properties, stiffness moduli, energy dissipation, particle breakage, cumulative settlement, pore water pressure, an‎d damping of calcareous san‎d from Hormuz Islan‎d was examined. Drained cyclic triaxial tests with a high number of loading cycles, ranging from 10,000 to 15,000, were conducted under various confining pressures, cyclic stress ratios, an‎d loading frequencies. To eva‎luate the mechanical changes, the samples were first subjected to drained static triaxial tests prior to cyclic loading, an‎d then retested under the same static conditions after cyclic loading. The results indicated that with increasing number of loading cycles an‎d cyclic stress ratio, both the internal friction angle an‎d shear strength decreased, with this reduction becoming more pronounced at higher cycles. The main cause of this degradation was found to be the abrasion of particle asperities an‎d the loss of interlocking between grains, leading to a decrease in the static strength of the soil. To assess particle breakage, post-test sieve analyses were performed. The results showed that although breakage increased with confining pressure an‎d cyclic stress ratio, the observed mechanism was primarily due to surface wear an‎d abrasion rather than complete particle crushing. This process resulted in smoother an‎d more rounded grains, further reducing the static strength. Dynamic test results showed that the secant shear modulus increased during the initial cycles an‎d then stabilized after several thousan‎d cycles. Moreover, the energy dissipated per cycle exhibited an increasing trend after approximately 1,000 cycles, reflecting a rise in damping ratio an‎d energy loss in subsequent cycles. Pore water pressure variations slightly increased during the early cycles; however, due to the drained condition of the tests, they gradually diminished to negligible values an‎d remained nearly constant thereafter. Overall, the findings demonstrated that prolonged cyclic loading alters the soil’s internal structure, leading to a gradual reduction in stiffness an‎d shear strength, accompanied by an increase in cumulative settlement potential.

ماسه كلسيم كربنات , بارگذاري ديناميكي بلندمدت , خردشدگي ذرات , نشست تجمعي , مدول برشي و ميرايي

Calcareous sand , long-term dynamic loading , particle breakage , cumulative settlement , shear modulus , damping

Roxsane Zamani

Mohammad Hassan Baziar