Numerical modeling of consolidation of unsaturated soils considering hydraulic hysteresis

The consolidation of soils is important to geotechnical engineering practice, such as when assessing the rate of settlement of shallow foundations, embankments, and landfills. In this paper, numerical analyses are performed to study the consolidation of unsaturated soils. The variations of excess pore-air and pore-water pressures and settlement with time are established by solving the governing equations. The flow and deformation of the different constituents of an unsaturated soil are fully coupled in the governing equations. The dependency of soil parameters, including the coefficients of permeability for air and water phases and the constitutive coefficients, is allowed to vary as changes to soil volume and suction occur. The effect of hydraulic hysteresis is investigated by considering different initial locations of the hydraulic states on the soil-water characteristic curve. It is shown that the different initial locations of hydraulic states result in different normalized instantaneous settlements and different initial excess pore pressures. The influence of the degree of saturation is also studied. It is shown that for the lowest degree of saturation, the most significant instantaneous settlement occurs and the total consolidation time is longest. The results of this study provide new insights into unsaturated soil consolidation. This is important because the hydraulic loading history and degree of saturation of the soil should be considered when assessing the rate and magnitude of consolidation settlement.