The rock-based sea area has great prospect of development and construction of offshore wind farms (OWFs), and the mainstream construction sites of OWFs in China have shifted from the soil-based seabed to the rock-based seabed area. Previous studies about mechanical properties of seabed materials and bearing characteristics of pile foundation in OWF mainly focus on the submarine soil-based seabed, resulting in lack of direct reference for the construction of offshore wind power in the rock seabed. Therefore, the study concentrates on the investigation of failure criterion of submarine completely weathered granite (CWG) of offshore wind farms in rockbased sea area under cyclic loads. Firstly, dynamic triaxial tests are carried out, and two unique development modes of CWG are revealed under different cyclic loads. The experiments analyze insight stiffness attenuation law and establish the prediction model of stiffness attenuation based on the logarithm formula. More critical, a unique development law of damping ratio of submarine seabed materials is discovered and discussed, and two cyclic failure criteria based on cumulative strain and dissipated energy are put forward to divide the critical CSR under cyclic loads, which gives helpful reference for the construction of offshore wind farms in rock-based sea area.

This study focused on exploring the specificity of mechanical behavior for completely weathered granite, as a special soil, by consolidated drained triaxial tests. The influences of dry density (1.60, 1.70, 1.80 and 1.90 g/cm(3)), confining pressure (100, 200, 400 and 600 kPa), and moisture content (13.0%, that is, natural moisture content) were investigated in the present work. A newly developed Duncan-Chang model was established based on the experimental data and Duncan-Chang model. The influence of each parameter on the type of the proposed model curve was also evaluated. The experimental results revealed that with varying dry density and confining pressure, the deviatoric stress-strain curves have diversified characteristics including strain-softening, strain-stabilization and strain-hardening. Under high confining pressure condition, specimens with different densities all showed strain-hardening characteristic. Whereas at the low confining pressure levels, specimens with higher densities gradually transform into softening characteristics. Except for individual compression shear failure, the deformation modes of the specimens all showed swelling deformation, and all the damaged specimens maintained good integrity. Through comparing the experiment results, the strain-softening or strain-hardening behavior of CWG specimens could be predicted following the proposed model with high accuracy. Additionally, the proposed model can accurately characterize the key mechanical indicators, such as tangent modulus, peak value and residual strength, which is simple to implement and depends on fewer parameters.

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.