Interaction of Forces on Caissons in Undrained Soils

In this paper the results of a numerical study on the behaviour of caisson foundations subjected to various combinations of loading are presented. A typical caisson has been used in this study with a length-to-diameter ratio of 2. The caisson is assumed to be embedded in a homogeneous soil deforming under undrained conditions. The performance of the caisson under separate axial, lateral and torsional forces was investigated first, followed by the interaction of these forces with each other. The ultimate capacity of the caisson under combined loading is presented in the form of failure envelope in the axial-torsional loading plane and axial-lateral, and lateral-torsional loading surfaces along the skirt of the foundation. It is shown that, although lateral capacity of the caisson is dependent on the location of the padeye, a unique normalised failure surface can be used to represent the capacity of the caisson under all combinations of axial, lateral and torsional loads regardless of the location of the padeye. KEY WORDS: Caisson foundations; undrained soils; failure envelope, finite element analysis