Comparison of air and water permeability between disturbed and undisturbed soils

Although soil structure and pore geometry characteristics largely control flow and transport processes in soils, there is a general lack of experiments that study the effects of soil structure and pore-space characteristics on air and water permeability. Our objective was to determine the dependency of soil permeability on fluid content for both water and air, and compare results for both disturbed (D) and undisturbed (UD) soils. For that purpose, we first measured the water permeability (k(w)) and air permeability (k(a)) for several intact UD soil samples. Subsequently, the same samples were crushed and repacked into the same soil cores to create the D equivalent for the same soil material. Measurements showed large differences between D and UD samples, confirming the enormous impact of soil structure and porespace characteristics on flow. The permeability of both fluid phases (air and water) was greatly reduced for the D samples, especially for soil air permeability due to its greater dependency on soil aggregation and structure. Soil water retention and permeability data were fitted to Campbell's and Mualem's pore-size distribution model, respectively. Regardless of soil disturbance, we showed that the tormosity-connectivity parameter, 1, for the water permeability (l(1)) and air permeability (l(2)) were different. This is in contrast to the general practice of using the same parameter value for both functions. The relation between l(1) and l(2) was largely controlled by soil structure and associated macroporosity properties.