An Efficient FE model for SSI: Theoretical background and assessment by predicting the response of large diameter monopiles supporting OWECs

An efficient technique called NVSM (Nonlinear Vertical Slices Model) for analyzing soil/structure interaction (SSI) problems is presented. This procedure approximates a full 3D problem into a series of 2D vertical interacting panels which can be solved using a standard 2D FE discretization, while allowing the slices interaction to be accounted for using the finite difference method. Duncan-Chang basic soil model is described first since it is simple to implement in a computer code, then, the extension of the VS Model to deal with nonlinear problems is detailed and supported by a flowchart giving the necessary steps of stress computations. The written Fortran computer code for predicting the response of large diameter monopiles supporting OWTs under combined loading is assessed against three case studies in which the authors used independently powerful commercial packages to study this kind of foundations embedded in offshore subsoils formed mostly of dense sand. An excellent agreement between the present predictions and those of the other numerical codes has been obtained.