Set-up of pile shaft friction in laboratory chamber tests

Although field evidence of increases in pile shaft friction over time (i.e. set-up) in sand is compelling, the observations are highly scattered and the mechanisms leading to the increases are poorly understood. Several attempts have been made to model the phenomenon using small-scale physical models in a controlled environment, but the investigations were hampered by numerous restrictions. This paper describes an improved small-scale model pile experiment designed to investigate the ageing effects of pile shaft friction in sand. Details of the experimental set-up adopted and procedures employed are presented. Results show that the phenomenon of pile set-up is successfully modelled and that load-displacement characteristics are in keeping with those observed in centrifuge tests. Although the ageing effects observed in this laboratory-scale physical model may not be directly applicable to field scale piles, comparative studies involving various influential parameters provide qualitative indications of the relative influence of a variety of parameters on the phenomenon.