Horizontal dynamic behavior of partially embedded pile groups in layer cross-anisotropic poroelastic saturated soils under lateral cyclic and axial coupling loadings

The paper presents an analytical approach for the horizontal dynamic impedances of partially embedded pile groups in layer cross-anisotropic poroelastic saturated soils under lateral cyclic and axial coupling loadings. However, early works on ocean engineering paid little attention to the anisotropy of seabed materials. In this study, Biot dynamic equations are adopted as the basic governing formulation for the porous cross-anisotropic seabed structure model. The formulations are decoupled by an analytical layer-element methodology accompanied with the convolution Hankel technique. Depending upon the derived soil stiffness matrix, the boundary element (BE) formulation is developed at pile-soil interface. The partially embedded pile finite element (FE) equation is derived based on the Timoshenko beam theory. Finally, the BE-FE formulations considering the pile-pile interaction are coupled to develop the dynamic impedance of partially embedded pile groups. The proposed solution is verified through comparisons against the analytical solutions of monopiles supporting wind turbines. The impacts of material anisotropy, soil structure stratification, pile embedded ratio, and pile-soil stiffness ratio on the lateral dynamic impedances are also presented. It is observed that piles in the soils with greater cross-anisotropic parameters show better impedance performance. Maximum displacement and bending moment exist at the soil surface. The stiffness of the top stratum determines the stratification effect on the impedance performance.