P ‐Ultimate for Undrained Analysis of Laterally Loaded Piles

A three‐dimensional collapse mechanism is described for analysis of the ultimate strength of laterally loaded piles under undrained conditions. The analysis is based on the upper‐bound method of plasticity theory. The mechanism combines a deforming conical soil wedge in the near surface with plane strain deformation at depth. Four optimization parameters are employed, which define the geometrical extent and spatial variation of the soil deformation. The mechanism is capable of rationally accounting for many complexities such as strength non‐homogeneity, soil‐pile adhesion, and suction on the back of the pile. Lateral force and pile top moment loading can both be accommodated. Parameter studies showing the effects of these features are presented along with comparisons of model predictions with recent centrifuge test results. An empirical prediction equation is fit to analytical results for typical soil conditions to provide a more convenient form of the analysis method. The empirical fit is demonstrated for cases of linearly increasing strength and for two‐layered soil systems.