Engineers Australia

Jacked piling in a soil subject to relaxation

Peter W. Mitchell

Abstract

Jacked piling at a site where pile relaxation occurred is described. The site was located in a coastal sand deposit in Forster, NSW. Based on earlier experiences with a sand site of similar geotechnical properties to that at Forster, relaxation was anticipated. Possible causes of relaxation are described. During installation of the piles, relaxation was detected and the techniques used to compensate for its effects are outlined. By jacking the piles to a pre-determined depth, by using termination criteria involving unload-reload cycles with relaxation periods of varying times and by monitoring the remobilised jacking force during load cycling, the relaxation effects were quantified, and the piling was completed successfully. The advantages of jacked piling in cases of relaxation are illustrated.