An Optimized Pore Network Model for Unsaturated Soil Permeability Determination

Abstract

Unsaturated soils consist of air and water within the porous space, and hydraulic conductivity and air permeability are essential characteristics. The relative permeabilities of various phases affect various phenomena like settlement rate, volume change, wetting collapse, etc. The common predictive models for relative permeability functions ignore the intricacy of pore structure and treat soil as a bundle of capillary tubes, which is an overly simplified approach. In this study, pore network modeling (PNM) is used for determining relative hydraulic permeability. Such models mimic the porous structure of soil by representing voids as pores connected by narrow regions called throats. Relative hydraulic permeability depends on soil water content, soil structure, and pore connectivity, making the pore network conceptualization a more realistic modeling approach. However, the realism of PNM depends on the correct representation of the pore structure of the soil. This study uses a genetic algorithm-based optimization technique to construct a pore network model of unsaturated soil. The drying soil water retention curve is used to calibrate the structural parameters of the pore network, such as pore size distribution and pore connectivity. The model determines the wetting soil water retention curve and relative hydraulic permeability.