Effects of Hydraulic Hysteresis and Drainage Conditions on Bearing Capacity of Unsaturated Soil Shallow Foundations

In this paper numerical analyses are performed to estimate bearing capacities of unsaturated soil shallow foundations by implementing an effective stress based finite element formulation. It is shown that the bearing capacity of these foundations increases due to suction. The effects of hydraulic hysteresis and different drainage conditions are investigated. It is found that the bearing capacity is dependent on the hydraulic loading history of the soil. It is also shown that a constant contribution of suction to the effective stress and strength condition (also referred to as a constant χs condition) provides a good approximation to a constant suction condition and a constant moisture content condition. When foundation loading occurs quickly, meaning a constant moisture content condition prevails, the χs magnitude can be assumed to be equal to the initial in situ value to simplify the calculation of bearing capacity.