Performance of piles with enlarged bases subject to uplift forces

The influence of embedment, base diameter, and backfill density on the uplift behaviour of piles with enlarged bases embedded in sand was investigated in a centrifuge. Comparitive tests on straight-shafted piles are also reported. For piles in dense sand, sensible agreement was found with earlier research on anchor plates and published field data. However, uplift capacities in loose sand were considerably lower than previously observed for anchor plates. A number of theories for anchors considerably overpredict the observed capacity for belled piers in both dense and loose sand, although in the case of dense sand, reasonable values are obtained using an empirical equation derived from centrifuge tests on anchor plates and a finite element based design approach. The normally conservative vertical slip-surface model is alone in providing reasonable agreement with the surprisingly low observations for piles in loose sand. Key words: piles, uplift capacity, centrifuge tests, sand.