Hyperbolic model to evaluate uplift force on pile in expansive soils

The piles in expansive soils would experience uplift force on the shaft of the piles due to the swelling of the soils. For a given soil, the magnitude of interface shear stress (uplift force) on pile depends on the interface friction between the pile material and the soil, normal stress acting on the pile surface and the magnitude of swelling, which in turn creates the relative movement at the interface between the soil and the pile material. The hyperbolic representation of stress strain curves has been found to be a convenient and useful means of representing the non-linearity of the stress strain curves of soils and forms an important part of the stress strain relationship. In this paper a simplified hyperbolic model is proposed to evaluate the pile uplift in expansive soil. The hyperbolic model is developed based on the model pile uplift tests, interface shear tests and consolidation test results. The interface shear stress is also evaluated using a program PIES (Axial response of Pile In Expansive Soils). Both the analytical studies gave a good correlation of interface shear stress profile obtained by laboratory studies. Finally a design procedure is proposed to evaluate the uplift force along the shaft of pile in expansive soils.