In conventional geotechnical engineering, the pull out of pile is always blamed only on the shear failure of the soil caused by the uplift force developed from the tip of the pile. For the belled pile, however, the enlarged foundation plays an important role to against the compression/uplift load, and the current theories for estimating the uplift capacities of the pile were found more than 50% relative error from measured. In this study, a new method for estimating the ultimate uplift capacity of the belled pile embedded in sandy soil was developed by taking into account the elastic/plastic behavior of the soil around the belled pile. It assumes that during the pull out process of the pile, the soil above the enlarged base is firstly subjected to an upward compression and causes a local soil consolidation which might affect the development of resultant failure surface of the soil around the pile. The starting location of failure surface is allowed to develop at a distance away from the pile surface. With 37 sets of experimental/field tests data, the development of the failure surface with curved slip-surface was suggested to start at the location of 0.67 of the radius of the enlarged base from central axis of the pile. The new method shows good approach with relative error lesser than 25% which is better than previous theories.

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