A numerical study of capacity and stiffness of circular skirted foundations in clay subjected to combined static and cyclic general loading

Abstract

Skirted foundations have been widely applied as offshore foundations for several decades. In design, the use of failure envelopes is convenient for assessing stability under combined loading. A large number of studies on failure envelopes exist in the literature based on experiments and numerical analyses. Most of these studies focus on ultimate capacity and static loading. This paper presents a numerical study focusing on cyclic degradation and failure envelopes for skirted foundations subjected to combined cyclic and static loading. It was found that the shapes of the failure envelopes are little affected by degradation expressed by the number of equivalent cycles. In addition to failure envelopes, contours of displacements were computed in the three-dimensional load space (vertical, horizontal and moment load) for a more complete description of the response. As an example, the well-defined cyclic contour diagrams of Drammen clay were utilised to demonstrate how foundation response diagrams can be established. The database is accompanied by a simplified procedure to account for cyclic degradation through equivalent number of cycles, different normalised load–displacement response and variation in foundation geometry. The framework of procedures can be used to estimate foundation stiffness and capacity and the results can serve as a basis for the development of foundation macro-element models.