Bearing capacity evaluation for shallow foundations on unsaturated soils using discretization technique

Bearing capacity evaluation for shallow foundations is conventionally completed according to the equations derived for dry or saturated soils neglecting the effect of matric suction. However, many shallow foundations are mostly constructed upon the soil layer above the groundwater table, where a large portion of soils under shallow foundations is in fact in unsaturated conditions. The failure of shallow foundations is usually related to shear failure which is one of the main engineering properties required in foundation design. The shear strength of unsaturated soils depends on the matric suction which usually changes with depth. Since the discretization technique of limit analysis is particularly suitable for considering the variation of soil parameters, the bearing capacity for shallow foundations considering the shear strength of unsaturated soils is therefore evaluated by this technique. The results obtained by the present technique are compared with the ones obtained from different authors, and good agreement is observed. Then a parametric analysis is performed using the present technique, and the bearing capacity for shallow foundations are given considering different soil types, foundation widths, effective internal friction angle φ′, air-entry pressure 1/α with various n values, different water table depth with surface flux boundary conditions, different unit weight of soil γ, and surcharge load q0. Some useful conclusions are given and a useful method is therefore provided for the bearing capacity evaluation of shallow foundations on unsaturated soils.