Undrained Stresses and Deformations under Footings on Clay

Axisymmetric finite element analyses using a total stress, minimum potential energy approach, were carried out to predict undrained stress-distribution and load-deformation behavior of a circular footing resting on clay. The stress-strain data obtained through laboratory tests on simulated field elements were approximated by a bilinear elastic, perfect plastic model, for use in the analyses. It was found that the type of finite element analysis was incapable of correctly computing simultaneously both stresses and deformations from a single analysis. Very good prediction of stress distribution could be obtained by keeping the Poisson's ratio constant throughout in the analysis. On the other hand, computed deformations agreed very well with the measured values when, in the nonlinear analysis, Poisson's ratio was adjusted whenever there was a change of stress-strain modulus, keeping the bulk modulus constant.