Procedures for quick estimation of hydraulic conductivity of unsaturated soils

Abstract

This paper describes a heuristic approach that combines a limited number of experimental measurements with the random finite-element method (RFEM) to accelerate significantly the process of measuring the hydraulic conductivity of unsaturated soils. A microstructure-based RFEM model is established to describe unsaturated soils with distribution of phases based on their respective volumetric contents. The intrinsic hydraulic properties of each phase (soil particle, water and air) are applied based on the microscopic structures. The intrinsic permeability of each soil phase is first calibrated from soil measured under dry and saturated conditions, which is then used to predict the hydraulic conductivities at different extents of saturations. The results match closely the experimental data. The pore size parameter was obtained from the variations in hydraulic conductivity with degree of saturation; from this, the soil-water characteristic curve (SWCC) is predicted. The results show that the SWCC estimated matches very well with experimental data. Overall, this study provides a new modelling-based approach to predicting the hydraulic conductivity function and SWCC of unsaturated soils based on measurement at completely dry or completely saturated conditions. An efficient way to measure these critical unsaturated soil properties will benefit introducing unsaturated soil mechanics into engineering practice.