Shakedown analysis of pile foundations under cyclic lateral loadings

Abstract

Pile foundations for many infrastructures, such as bridges, oil rigs, electricity towers, wind, and wave turbines, sustain cyclic lateral loads from wind or wave actions. The long-term response of pile foundations under cyclic lateral loading conditions is one key factor to consider in the design, which is commonly explored by cyclic pile load tests or step-by-step numerical procedures with empirical degradation factors. Shakedown analysis provides an alternative and efficient means of predicting limiting loads of the pile foundations against excessive accumulated permanent deformation under cyclic lateral loads. In this study, a generalised shakedown approach is proposed, with flexible linear modifications, to solve the stability problem of three-dimensional geotechnical structures under cyclic loads. It provides a novel concept of pursuing the final residual stresses at the shakedown limit in one cycle period. The co-operation between ABAUQS and Python in this approach offers a great potential for extended applications. The generalised shakedown approach is first implemented into classical problems with Von-Mises, Tresca, and hyperbolic Mohr-Coulomb criteria considering an associated or a non-associated flow rule. In central-holed plate problems, the approach demonstrates its remarkable performance for the accurate and efficient prediction of shakedown behaviour. The general feasibility of the approach is further proved by solving pavement problems. Both the shakedown limits and the residual stress distributions against depth are in excellent agreement with theoretical results. The main focus of the current research is concerned with the shakedown behaviour of pile foundations under cyclic lateral forces. A series of well-designed models is utilised to examine the effects of pile geometry, soil property, and interaction parameters. Both rigid pile and flexible pile are studied. The results reveal a distinguished capability of the two piles enduring repeated moment, horizontal forces, or a combination. The ratio of shakedown limit to plastic limit decreases with the rise of length to diameter ratio. Moreover, a two-way repeated loading yields a smaller shakedown limit than a one-way cyclic loading. Finally, a study of pile group efficiency is carried out using the current approach to check the influence of group effects on the shakedown limit. A general pile group design procedure is followed according to the previous conclusions, which demonstrates the great importance of shakedown analysis in the design of pile foundations.

Date of Award	8 Jul 2021
Original language	English
Awarding Institution	Univerisity of Nottingham
Supervisor	Juan Wang (Supervisor) & Fangfang Zhu (Supervisor)