Uplift capacity of strip plate anchors in unsaturated clay

Numerous studies have been reported in literature for plate anchors in saturated or dry clays. However, in practical scenario the soil overlying the anchor plate in most of the cases is in unsaturated state, and even then, no study seems to be available for anchors in unsaturated soil. The uplift capacity depends on the resistance of soil overlying the anchor plate, which is in turn affected by the shear strength of soil and varies with variation in the matric suction owing to changes in surface flux conditions and position of the water table. Hence, it has been planned to study the uplift capacity of horizontal strip plate anchors buried in unsaturated clay in this paper. The stress-based limit analysis with the help of finite elements and second-order cone programming has been used for performing the analysis considering the variation of matric suction with depth above the water table under various surface flow conditions (evaporation, no flow and infiltration). Unified effective stress approach-based modified Mohr-Coulomb yield criterion was used to include the influence of stress due to matric suction to the ultimate failure state. The uplift capacity was expressed in terms of a non-dimensional uplift capacity factor, which has been found to be dependent on the embedment depth-to-width ratio of anchor, shear strength parameters of soil, water table position, various flow conditions and their flow rate. The effect of other parameters like air-entry pressure and pore-size distribution parameters, degree of saturation, specific gravity of soil solids, and soil-anchor interface roughness has also been examined and was found to be insignificant. The solutions were presented for an immediate breakaway condition, i.e., considering that the contact between anchor and underlying soil mass is separated at ultimate failure.