Basal anti-heave stability of foundation pits in unsaturated soils

It is known that soils surrounding a foundation pit are commonly in an unsaturated condition and retaining wall displacement routinely rotates around wall bottom (i.e., RB displacement mode). The bearing capacity of strip foundations at wall bottom with a single-sided sliding surface and the vertical anti-sliding force of wall-soil system under RB displacement mode with an overall down-sliding were first presented in the framework of the two stress state variable theory for unsaturated soils. For uniform and linear suction profiles, the limit equilibrium method was then adopted to provide a solving process on the safety factor against basal heave of foundation pits in unsaturated soils, respectively. Finally, comprising verifications to theoretical solutions reported in the literature with an engineering case of foundation pits, and influences of different wall displacement modes were explored. The results show that the proposed safety factor against basal heave of foundation pits accounts for soil unsaturated characteristics and RB displacement mode of a retaining wall. The proposed safety factor compares reasonably well with available theoretical solutions of both the foundation bearing capacity model and the limit upper bound approach, and it can naturally reduce to that of saturated soils. The vertical anti-sliding force and the safety factor against basal heave of foundation pits under RB displacement mode of retaining walls are smaller than those under an in-situ state. Safety factor against basal heave of foundation pits is the minimum one and conservative for simplified calculation of unsaturated soils taken as saturated soils ignoring unsaturated strength characteristics.