This paper presents the results of a numerical study on the effects of torsional loads in reducing the vertical and lateral bearing capacity of caisson foundations. The caisson is assumed to be embedded in a homogeneous soil deforming under undrained conditions. The performance of a typical caisson foundation under axial, torsional and lateral forces is investigated followed by the interaction of torsion with the other two components of loading. The ultimate capacity of the caisson under combined loading is presented in the form of failure envelopes in the axial-torsional and the lateral-torsional loading planes. The results of this study show that generally torsional forces significantly affect the vertical and lateral capacity of caisson foundations. However, their effects on lateral capacity can be ignored in some cases of practical significance, i.e., those where the horizontal line of action of the force applied to the padeye passes within about 0.2 of a diameter of the vertical axis of the cylindrical caisson.
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