The offshore wind turbines (OWT) are subjected to cyclic loads, such as ocean waves and wind, over extended periods. The soil surrounding the pile experiences bi-directional cyclic shear. As a result of the low-frequency and long-term loading in the pile-soil interaction, the cumulative deformation of pile foundation increases, posing a risk to the operational safety of wind turbine system. The soil around the piles is distributed with soft clay and clay layers. To study the cumulative deformation properties of clay under complex stress states. A series of tests are conducted, the variation of resilient modulus under different cyclic stress levels and confining pressures is analyzed based on test results. Then an empirical model uniformly reflecting strain-hardening and strainsoftening properties of clay is proposed. The variations of model parameters are investigated. Then the established empirical model is used to modify the maximum elastoplastic modulus at each unloading within the bounding surface constitutive model, a parameter reflecting the magnitude and rate of strain accumulation is also introduced. This method is characterized by a simple expression and requires fewer model parameters. Finally, the predicted results of modified constitutive model are compared with test results to verify the validity of the established model.

In this paper, the research progress made in the methods used for assessing the internal stability of landslide dam soils was reviewed. Influence factors such as the gradation of soil and the stress state in the soil in different analysis methods were discussed, as these can provide a reference for the development of more accurate methods to analyze the internal stability of landslide dam soils. It focuses on the evaluation of internal stability based on the characteristic particle size and fine particle content, hydraulic conditions such as the critical hydraulic gradient and critical seepage velocity, and the stress state such as lateral confinement, isotropic compression, and triaxial compression. The characteristic particle size and fine particle content are parameters commonly used to distinguish the types of seepage failure. The critical hydraulic gradient or seepage failure velocity are necessary for a further assessment of the occurrence of seepage failure. The stress state in the soil is a significant influence factor for the internal stability of natural deposited soils. Although various analysis methods are available, the applicability of each method is limited and an analysis method for complex stress states is lacking. Therefore, the further validation and development of existing methods are necessary for landslide dam soils.

The fatigue and damage characteristics of frozen soil under cyclic loading are highly dependent on the three-dimensional (3D) stress state, due to the anisotropic properties of the ground. Measuring and researching the deformation behavior and fatigue failure characteristics of frozen soil under complex 3D cyclic stress states are significant for the stability assessment of frozen soil when it is subjected to earthquakes and vehicular traffic. In this paper, a hollow cylindrical apparatus was used to simulate a cyclic stress state with constant values of principal stress direction angle (alpha), coefficient of intermediate principal stress(b), and amplitude of the first principal stress under -6degree celsius conditions. The influences of 3D stress parameters (alpha and b) on the deformation behavior, damage evolution, and fatigue failure characteristics of frozen silty clay were systematically investigated. The results indicated that the deformation of the samples was dominated by axial strain, when alpha < 15 degrees and b = 0. Furthermore, as the value b increased, both the accumulated axial strain and accumulated torsional shear strain exhibited a decreasing-then-increasing trend. When 30 degrees <=alpha <= 60 degrees, the deformation feature is primarily dominated by torsional shear direction. With the increase of the value b, the accumulated torsional shear strain increased rapidly, while the axial strain gradually decreases, and then in turn to compressive elongation deformation. The increase of 3D stress parameters leads to a decrease in accumulated torsional shear strain, absolute value of accumulated axial strain, number of cycles, and accumulated torsional shear dissipated energy density at the failure of frozen soil. This indicated that under cyclic stress conditions, the increase of 3D stress characteristic parameters accelerates the damage evolution and fatigue failure process of frozen soil samples. Essentially, the increase of 3D stress parameters accelerates the damage of soil particle and ice lens structures in horizontally layered and the growth of micro-crack of frozen soil, thereby reducing the transverse shear resistance of frozen soil samples.