Evolution of Water Retention Characteristics in Bio-Geochemically Altered Unsaturated Soils: A Pore-Scale Study

Abstract

Biogeochemical processes in subsurface can dramatically alter the behavior of multiphase fluid flow and the hydrodynamics of porous media by bio-clogging. There exist analytical solutions such as soilsuction – saturation equations which can be used to predict the water retention curve relations in unsaturated soils. However, due to the complexity of various biogeochemical products, their pore-scale behavior and their interplay with pore structure, such analytical solutions would not provide accurate predictions. In this study, a large database of pore-networks were generated by adjusting the statistical and spatial pore and tube size distribution of the networks resembling various levels of bio-clogging. Numerical simulations including the evolution of pore structure, water retention relationship, and air invasion dynamics during desaturationwere explored. The numerical simulations verified that local pore-clogging leads to the development of isolated pore clusters and impermeable zones. The evolution of impermeable zones results in the formation of preferential flow paths towards the mobile zones for the multiphase flow problems. Using parallel computation, the critical predictors of water retention curves in bio-clogged porous media are found.