Time effects on shaft capacity of jacked piles in sand

This paper examines the effects of time on the shaft capacity of jacked piles in sand through an experimental program performed at three separate test sites in Western Australia. A total of 18 instrumented pile tests were conducted to track the changes of radial stress on the pile shafts, as well as shaft friction, up to a maximum of 72 days after installation. The results confirm that the gains in shaft capacity of jacked piles are small after a period of about 1 day. This observation is in keeping with limited available case history data, but is in stark contrast to the significant capacity gains reported for driven piles. Further examination reveals that set-up effects for jacked piles in sand are relatively significant within one day of installation, and that the increased friction is associated primarily with larger increases in radial effective stress during shearing.