Active earth force in ‘cohesionless’ unsaturated soils using bound theorems of plasticity

Granular ‘cohesionless’ soils above the water table are partially saturated but are commonly assumed to be dry in geotechnical practice. The ‘dry soil’ assumption neglects the effect of suction on shear strength and soil structures are therefore over-designed. This paper presents an approach to the analysis of collapse of soil structures above the water table based on the upper and lower bound theorems of plasticity. As an example, the active earth force on a retaining wall has been calculated and compared to the value obtained from the classical ‘dry’ approach.