Abstract: As a new type of deep-water offshore foundations, suction caisson foundation is widely used to fix offshore structure or facilities. Under such a circumstance, suction caisson foundations are frequently subjected to pullout forces. Therefore the ultimate bearing capacity and performance of such foundations under combined application of both vertical and horizontal components of pullout are one of the key issues in the design and construction of offshore structures and facilities. However, the performance of such foundations has been not well understood; and current methods of evaluation and design cannot meet the increasing requirement of engineering practice. Therefore a numerical procedure based on FEM for evaluating the uplift bearing capacity behavior of suction caisson foundation is developed. On the basis of the multi-purpose finite element analysis software ABAQUS, step-by-step loading procedure is numerically implemented to simulate the progressive deformation process and failure mechanism. During the pullout of caisson foundation, the normal consolidated clay is under fully undrained state. The general shear failure of caisson foundation is characterized by an ultimate collapse pattern due to bearing capacity which is opposite to traditional failure mode of foundation subjected to vertical compressive load. It is assumed that the soils surrounding the caisson foundations are in undrained condition during pullout and their original strength is fully mobilized. Then comparative numerical computations are performed for different aspect ratios of caisson foundation to determine the ultimate bearing capacity of caisson foundations under single action of vertical pullout or horizontal pullout. The authors’ numerical results are compared with the solutions obtained by current theoretical or numerical analyses. It indicates that the uplift ultimate bearing capacity by finite element numerical method is accordance with by theoretical method, and the horizontal ultimate bearing capacity has small variant.

Key words: suction caisson foundation, finite element analysis, ultimate uplift bearing capacity, pullout load, bearing capacity theory