Generalized Density‐Corrected Model for Gas Diffusivity in Variably Saturated Soils

Accurate predictions of the soil‐gas diffusivity ( D p / D o , where D p is the soil‐gas diffusion coefficient and D o is the diffusion coefficient in free air) from easily measureable parameters like air‐filled porosity (ε) and soil total porosity (ϕ) are valuable when predicting soil aeration and the emission of greenhouse gases and gaseous‐phase contaminants from soils. Soil type (texture) and soil density (compaction) are two key factors controlling gas diffusivity in soils. We extended a recently presented density‐corrected D p (ε)/ D o model by letting both model parameters (α and β) be interdependent and also functions of ϕ. The extension was based on literature measurements on Dutch and Danish soils ranging from sand to peat. The parameter α showed a promising linear relation to total porosity, while β also varied with α following a weak linear relation. The thus generalized density‐corrected (GDC) model gave improved predictions of diffusivity across a wide range of soil types and density levels when tested against two independent data sets (total of 280 undisturbed soils or soil layers) representing Danish soil profile data (0–8 m below the ground surface) and performed better than existing models. The GDC model was further extended to describe two‐region (bimodal) soils and could describe and predict D p / D o well for both different soil aggregate size fractions and variably compacted volcanic ash soils. A possible use of the new GDC model is engineering applications such as the design of highly compacted landfill site caps.