Significant residual stress may be formed along a jacked pile during installation. Field tests are conducted on a 26 m pile jacked into sandy soil

involving observations on the variations in residual stress in a 212 d test period after pile construction. The test scheme includes a cyclic loading test

installation of three adjacent piles

a reloading test and a relatively long-term rest. The results show that the residual stress of pile is further accumulated in the cyclic loading tests as the number of loading cycles and the level of cyclic loading increase. The magnitude of residual stress

however

is reduced by the tensile effect of jacking the adjacent piles. Such effect is found to be the maximum when the penetrating pile tip approaches the observed depth. The residual stress of pile tends to decay to a stable value for a relatively long period. The influence of time on the residual stress of pile is mainly related to the creep behavior of sandy soil that weakens the soil arching effect around pile and reduces the contact pressure at the tip of pile.