Plasticity Model for Cyclic Axial Pile Response with Back-Analyses of West Delta Pile Tests

Abstract

A two-surface bounding surface plasticity model for the undrained axial pile response in fine-grained soils is described and used in the back-analysis of full-scale pile tests using the empirical one-dimensional t-z spring method to represent the axial soil resistance. A damage mechanics component incorporates degradation of resistance as a result of accumulated plastic displacement. The computed pile shaft-resistance damage along the pile allows estimation of its evolving capacity. The model produces evolving local cyclic and average resistances mobilized along the pile that are consistent with the observed test responses. The model is used to investigate the cyclic capacity of the same pile conditions under combinations of mean and variable loads. The implications of the test data and modeling results on the design of tension piles are discussed.