Undrained bearing capacity of ring foundations on two-layered clays

This paper presents the results of a numerical investigation into the undrained vertical bearing capacity of rough ring foundations resting on two-layered clays of both homogeneous and linearly increasing shear strength profiles. Small displacement finite element predictions are compared with the available empirical, analytical and numerical solutions, and expressed in the familiar form of bearing capacity factors reflecting the coupling effects of the dimensionless parameters related to foundation internal opening, relative top layer thickness, strength difference between two layers, and strength non-homogeneity. The depth beyond which the shear strength of the bottom layer does not affect the bearing capacity, defined here as critical depth ratio, is identified. The failure mechanisms of ring foundations are also discussed in terms of the displacement pattern.