Predictions of the uplift response of model belled piles in geogrid-cell-reinforced sand

Abstract

Breakout factors from a series of laboratory pullout tests on model-belled piles (or enlarged base footings) in geogrid-cell-reinforced sand, which included tests on various model geometries and sand densities, are examined. The concept of effective diameter and effective embedment ratio based on the diameters of both belled piles and geogrid-cell-reinforcement is introduced which provides a pattern of uplift behaviour consistent with previous findings for anchor-type foundations. A unique relationship between effective breakout factor and effective embedment ratio is derived for a given sand density. Experimental breakout factors compare well with predictions from some existing theories for anchor foundations, while a simple approach based on the vertical slip surface model incorporating an uplift coefficient K=0.8√ K P yields close overall agreement with the laboratory data. A hyperbolic relationship is established between pullout load and displacement, which can be used to determine soil stiffness for use in non-linear analyses.