A direct FEA loading approach for combined failure envelope of foundations in cohesive soil

Abstract

Foundations, particularly offshore foundations, are subjected to multidirectional combined loading, making accurate failure envelopes essential for geotechnical design. Traditional methods for constructing these envelopes face significant challenges. This study presents a Direct Displacement Swipe (DDS) method that indirectly steers the displacement-space trajectory to conform to a prescribed load-space trajectory, implemented within a Finite Element Analysis (FEA) framework to improve accuracy and computational efficiency. Different from conventional swipe method, a truss element is used to simulate the rope, with one end connecting to the foundation and the other end for loading, resulting in the same direction of displacement and load. Validation across various types of foundations, including circular surface footings, suction caissons, tripod buckets, and composite pile-bucket foundations, covering a range of shallow to deep foundation categories, under diverse cohesive soil conditions, highlights its robustness. Comparative analysis shows the DDS method matches the accuracy of traditional approaches while significantly reducing computational costs. Additionally, it effectively captures both symmetrical and asymmetrical failure envelopes, where traditional methods often fall short. Therefore, the DDS method emerges as a practical, efficient, and reliable alternative for geotechnical design.