The influence of foundation geometry on the uplift behaviour of piles with enlarged bases

Abstract

Centrifugal model tests investigating the influence of shaft to base diameter ratio and bell angle on the uplift capacity of piles with enlarged bases (or belled piers) in sand are reported. Increases in the angle of bell and in diameter ratio both result in a decrease in net uplift capacity and failure displacement. This appears to account for observed differences in uplift capacity between belled piers and anchor slabs. Studies of failure mechanisms around models of belled piers and anchor plates show distinctly different behaviour characteristics between foundation types. The comparatively low uplift capacities observed for belled piers are attributed to a lesser degree of soil mobilization. An empirical design method for belled piers is proposed in which appropriate factors which account for foundation geometry are applied to a simple continuous anchor formula. Key words : piles, sand, uplift capacity, centrifuge, design.