Pile group in clay under cyclic lateral loading with emphasis on bending moment: Numerical modelling

Abstract

Pile foundations supporting major structures are often founded in soft compressible clays. Apart from usual super-structural loading, these piles are subjected to cyclic lateral loads originating from actions of waves, ship impacts, winds or moving vehicles. Such repetitive loading induces stress reversal in adjacent soft clay initiating progressive degradation in soil strength and stiffness. This not only deteriorates the pile capacity with unacceptable displacements, the bending moments also increase. Although past studies investigated the response of single pile under lateral cyclic loading, a detailed study on pile group in clay under cyclic lateral loading with emphasis on bending moment is of immense practical interest. This paper focuses on detailed study of the response of pile group in clay under cyclic lateral loading, with emphasis on bending moment, through numerical modelling via a three-dimensional dynamic finite element (FE) approach and simplified boundary element modelling (BEM). Comparisons of computed results with available test data imply that the results obtained by 3 D dynamic FE model are better than the BEM. Extensive parametric studies with field data indicate that pile bending moment has been significantly influenced by cyclic loading parameters (number of cycles, frequency and amplitude). Relevant conclusions are drawn from the entire study.

Keywords:

• bending moment
• clays
• cyclic lateral load
• numerical methods
• piles & piling

Acknowledgements

The authors acknowledge the in-kind support for providing the entire computational facility at the University of Technology Sydney, Australia. The infrastructural support received from Pinnacle Educational Trust, India is also acknowledged.

Disclosure statement

No potential conflict of interest was reported by the authors.

Appendix

Further details of the computer program LCYC has been given herein. The computer program was initially developed by the author for single pile in clay (Basack and Purkayastha 2007). The program was sufficiently upgraded to capture the pile group behaviour with emphasis on bending moment and renamed as LCYC. The flowchart of the program is included in Figure 13. The program consists of several iterative steps which include a number of major and minor loops. Separate subroutines are developed for piles under lateral static and cyclic loads.

Figure 13. Flow-chart of the program LCYC.