With the advantages of low construction costs and rapid installation, suction caissons are widely used as foundations in offshore engineering. This paper investigates the behavior of suction caisson foundations located in sandy soil under horizontal cyclic loads. The upgraded simple anisotropic sand constitutive model with memory surface (SANISAND-MS model) is employed to accurately capture the sand's cyclic behavior. To calibrate the parameters of the upgraded SANISAND-MS model, a series of triaxial drained monotonic and cyclic tests was performed. The effects of load idealization and loading sequence on the cyclic behavior of sand are studied based on the element test results, and the effects of load idealization on the cyclic response of suction caissons are studied from a finite-element simulation perspective. The triaxial test results indicate that load idealization slightly affects strain accumulation in both loose and dense sand. Based on simulation results, it is found that the loading sequence of load packages with varying amplitudes has a minor effect on the rotation accumulation of the suction caisson. The current load idealization method used in the engineering design practice of suction caissons is acceptable under drained conditions.

This study investigates the mechanical behavior of gravelly soil under various confining pressures using large-size triaxial cyclic tests and a novel constitutive model. Key properties analyzed include stress-dependent dilatation, nonlinear strength, cumulative plastic strain, cyclic hysteresis, hardening, and particle breakage. Experimental results show that confining pressure significantly affects volume deformation, strength, and failure modes. Specifically, volume deformation shifts from dilatation to contraction with increasing pressure, and failure modes transition from drum-shaped to compressive shear. The developed model integrates stress-dilatancy equations, plastic flow directions, and plastic moduli within the critical state soil mechanics framework, effectively capturing cyclic loading and unloading behaviors. A particle breakage index and a differential equation for void ratio evolution are included to reflect relative density changes. The material constants of this constitutive model are derived from large-size triaxial cyclic tests. The model's material constants are derived from large-size triaxial cyclic tests. Comparison with experimental data confirms the model's accuracy and potential applications in stress path analysis and complex engineering projects, demonstrating its adaptability to varying mechanical stress conditions.

A series of undrained cyclic triaxial tests were carried out on loose sand specimens, including encased and non-encased granular columns, to evaluate the cyclic behavior and liquefaction resistance of the ground improved by granular columns. It was found that using geogrid encasements could effectively reduce cumulative settlements and mitigate the liquefaction potential when its tensile stiffness was high enough. Another finding was the inefficiency of flexible geosynthetic encasements to delay and mitigate the liquefaction in granular columns with the possibility of clogging. Findings indicated that the improvement of a loose ground with encased granular columns not only decreased the liquefaction-induced ground deformation but also significantly reduced the effect of earthquake magnitude on the ground deformation. It was also found that using the granular column and encasing it with a high-stiffness encasement not only slowed down the rate of ground softening during the cyclic loading experience but also decreased the dissipation of energy.

The undrained cyclic behavior of rubber-sand mixture (RSM) is usually investigated under the cyclic loads with unidirectional shear stress. However, bidirectional shear stress exists in many engineering practices subjected to complex loads, under which the liquefaction resistance of soil may be overestimated. Furthermore, the soil behavior under bidirectional shear stress exhibits quite differently from that under unidirectional shear stress. Therefore, undrained cyclic behavior of RSM under bidirectional shear stress should be further investigated. In this study, several specimens made by RSM with different rubber contents (from 10 % to 30 % by volume) are consolidated under two conditions, K0 consolidation and the combination of K0 consolidation with consolidation shear stress (CSS). Subsequently, numerous tests are conducted under the unidirectional and bidirectional cyclic loading paths to investigate the cyclic undrained behavior of RSM. The results show that the bidirectional shear loads incur a larger normalized pore water pressure (PWP) than unidirectional shear loads. In addition, an energy-based method is employed to understand the relationship between cumulative energy and normalized PWP. During the stage of rapidly accumulating PWP, the dissipated energy required to generate the same normalized PWP is identical, and it is independent of the shapes of loading paths.

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.

The principal construction-area of offshore wind farm (OWF) in China has shifted from the soil-based seabed area to the weathered rock-based area. The current studies about construction materials of OWF mainly focus on the submarine soft-clay or sandy soil seabed, resulting in the design and construction of OWF in rock-based area cannot directly refer to the existing research conclusions and results recommended in standards. Therefore, this paper concentrates on the investigation of cyclic behavior of submarine completely weathered granite of offshore wind farms in rock-based sea area under cyclic loadings. The experiments analyze the cyclic stress-strain and stress path behavior, revealing two unique development modes under different dynamic loadings, i.e., the stable development mode and the destructive development mode. A unified forecasting model of pore water pressure with different development modes is established, and further research investigates insight critical failure stage by concentrating on pore water pressure. More critical, the unique mechanical properties and microscopic characteristics of completely weathered granite are clearly expounded by comparing with submarine soft clay and sandy soil. This gives the engineering suggestion of design value of OWT foundation in completely weathered granite seabed, and is a helpful reference for the construction of OWF in rock-based sea area.