Soil hydraulic functions determined from measurements of air permeability, capillary modeling, and high-dimensional parameter estimation

Prediction of flow and transport through unsaturated porous media requires knowledge
of the water retention and unsaturated hydraulic conductivity functions. In the past few
decades many different laboratory procedures have been developed to estimate these
hydraulic properties. Most of these procedures are time consuming and require significant
human commitment. Furthermore, multiple measurement techniques are typically
required to yield an accurate characterization of the retention and hydraulic conductivity
function between full and residual saturation. We present a more efficient and robust
approach to estimating the hydraulic properties of porous media. Our method derives an
optimized pore-size distribution from measurements of air permeability and using recent
advances in capillary modeling and high-dimensional parameter estimation. The section
diameters of different parallel capillaries representing the pore structure of a porous
medium are optimized with a multi-algorithm optimization method by comparing measured
and modeled air permeability values. The optimized pore model is subsequently used
to predict the water retention and water permeability functions. The predicted soil hydraulic
properties are shown to be in excellent agreement with experimentally determined data
from an unconsolidated porous medium column. Our approach does not impose any functional
form of the hydraulic properties and requires only measurements of air permeability.