Abstract: The stiffness degradation model of soft clay based on bidirectional cyclic loadings was presented to analyze the cumulative lateral displacement of single pile foundation under lateral and vertical cyclic loadings. The finite element software Abaqus was used to realize the stiffness degradation by secondary development method and study cumulative lateral displacement of single pile foundation under lateral and vertical cyclic loadings. Results indicate that under vertical and lateral cyclic loadings, lateral displacement at single pile head is larger than that only under horizontal cyclic loading. Minimum horizontal cyclic loading ratio is found under the analysis. When the horizontal cyclic loading ratio is smaller than the minimum, lateral displacement cannot cumulate in single pile foundation. There is a critical value of vertical cyclic loading in terms of its influence on pile lateral deformation. Lateral displacement of pile cannot be seriously affected by vertical cyclic loading when it is below that critical value.

Key words: bidirectional cyclic loadings; single pile; lateral displacement; stiffness degradation; cyclic loading ratio