Influence of axial load on lateral pile response in liquefiable soils Part I: physical modelling

Current research work into the behaviour of piled foundations in liquefiable soils has concentrated on the response to lateral inertial and kinematic loads. It has recently been demonstrated in the literature, however, that an alternative mechanism exists, whereby piles carrying significant axial loads may become unstable as lateral soil restraint is lost owing to earthquake-induced soil liquefaction. In the work presented here and in a companion paper, this effect is examined in greater depth, particularly regarding the integration with and effects on the lateral response of piles such that the two effects can be treated under a unified framework. Dynamic centrifuge testing was used to investigate pile instability by examining the behaviour of pile groups with lateral deflections. Amplification of these deflections was observed to occur during liquefaction, although currently available simple idealisations of soil behaviour were found greatly to over-predict these amplifications when compared with the experimental observations. The response of the soil to such large-deformation events was determined for use in more sophisticated numerical modelling presented in the companion paper. Relative pile-soil flexibility was found to have a strong influence on amplifications occurring in the tests. Ultimately, at high axial load or amplification, unstable collapse ( bifurcation) was found to occur both during earthquake shaking, and afterwards owing to excess pore pressure migration altering the strength of the supporting soil surrounding the piles.