Effect of partial saturation on the stability of shallow foundations above the water table

Granular ‘cohesionless’ soils above the water table are partially saturated but are commonly assumed to be dry in geotechnical practice. Accordingly, ‘drained’ shear strength is calculated by replacing the ‘saturated’ effective stress with the total stress. The ‘dry soil’ assumption neglects the effect t of suction on shear strength and, as a result, geo-structures are over designed. To investigate the implications of this assumption, this paper presents an approach to calculate the bearing capacity of shallow foundations above the water table taking into account the effects of partial saturation. This approach is based on the upper bound theo-rem of plasticity. The bearing capacity of a strip foundation in granular soils is calculated and the solution obtained by taking into account the effects of partial saturation is compared with the solution obtained from the classical ‘dry’ approach