Elastic Solutions of Circular Foundations Under Combined Loading

The design of shallow foundations for wind turbines is typically governed by serviceability and fatigue limit states. To estimate the deformations of shallow foundations under working loads, existing design standards generally employ analytical uncoupled isotropic elastic solutions based on idealized soil conditions. However, many natural soil deposits exhibit some degree of stiffness anisotropy due to their deposition and complex stress history. This study has investigated coupled elastic stiffness coefficients for circular shallow foundations founded on cross-anisotropic soils under combined VHMT loadings (vertical, horizontal, moment and torsional) using finite element analysis. A three-parameter anisotropic soil model was applied to the problem. The study extensively explores the effects of soil stiffness non-homogeneity (i.e. linear increase of elastic modulus with depth) and foundation embedment on the foundation stiffness coefficients. Fitted expressions of these stiffness coefficients were also derived. In addition, a practical application using the proposed stiffness coefficients was presented to demonstrate the effects of soil stiffness anisotropy on the responses of a typical large wind turbine shallow foundation.