Load Transfer Mechanism Variations of Bored Piles in Collapsible Loess Subjected to Water Infiltration

Abstract

Currently, bored piles are commonly designed based on saturated soil mechanics with an assumed drained condition, even though in most cases the loess is unsaturated. Upon water infiltration, the matric suction reduction and matric suction reduction-induced soil collapse deformation could cause significant changes to the pile load transfer mechanisms. In order to investigate the mechanical behaviors of bored piles in collapsible loess subjected to water infiltration, a large-scale model test was performed. The testing results indicated that the continuous pile settlement observed before the wetting front proceeded to the pile base, and the corresponding changes in the pile load transfer mechanism were mainly attributed to the changes in the magnitude and direction of pile shaft friction. While as the loess beneath the pile base was gradually saturated, the reduction in pile base stiffness further accelerated the pile settlement until the sum of pile base resistance and pile shaft friction failed to balance the service load applied on the pile head. Considering the influences of loess collapsible deformation, as well as the contribution of matric suction to the mobilization of pile shaft friction and pile base resistance, the traditional load transfer method was modified to extend its application to bored piles in unsaturated collapsible loess subjected to water infiltration. The relatively good agreement between testing and predicting results indicated that the modified load transfer method could be a powerful tool in the design and bearing behaviors evaluation of bored piles in collapsible loess.