Simple approach for including foundation-soil-foundation interaction in the static stiffnesses of multi-element shallow foundations

Abstract

In common engineering practice, foundation–soil–foundation interaction of shallow foundations is frequently ignored. This is presumably for cost/benefit reasons, since computationally demanding finite-element and/or boundary element models are required for that purpose, and its effects are usually assumed to be negligible. In this sense, the present paper provides a simple and inexpensive way of incorporating foundation–soil–foundation interaction through a numerically explicit stiffness matrix formulation. The necessary ingredients for homogeneous and non-homogeneous (shear modulus power-law variation with depth) half-spaces are given. The proposed approach is then applied to offshore wind turbines’ multiple suction caisson foundations (tripod and tetrapod), where it is observed that the foundation–soil–foundation interaction is significant. Its range of validity is also established, and valuable ready-to-use closed-form formulas for the correction factors of the stiffnesses of tripod and tetrapod groups are also derived. The methodology is applicable as long as the spacing between foundations is somewhat greater than the foundation depth.