Numerical investigation on three-phase flow in unsaturated soil considering porosity effects on soil hydraulic properties

Abstract

Ground contamination by mineral oil and hydrocarbons is a serious problem worldwide. These non-aqueous phase liquid (NAPL) represents long-term contamination sources to the soil, groundwater, and ecological environment. In the existing numerical simulation models utilized in most simulation programs, the relation between porosity and the hydraulic properties of unsaturated soils is highly simplified as nonlinear. However, the nonlinear porosity effect on soil permeability and the capillary pressures cannot be well considered in this way. In this study, a new mathematical model has been developed to incorporate porosity effects into the hydraulic properties of soils, including the retention behaviour and permeability function of NAPL and water. This model has been implemented in MATLAB using the finite difference method and verified by a centrifuge test about NAPL infiltration. Then, a series of parametric studies will be carried out to investigate the multi-phase flow under a continuously leaking NAPL source. The influence of porosity magnitude and distribution will be investigated. Special attention will be paid to the influence of porosity distribution by soil consolidation on NAPL flow, which is often ignored by the existing simulations using constant porosity values.