SIMULATING DIFFUSION IN A BOOLEAN MODEL OF SOIL PORES

The diffusion of gas through a model of the structure of soil pores was simulated on a computer. This was done to test the model's usefulness for studying diffusion in real soil and to obtain insights into how soil pore geometry affects diffusion. A model of randomly-placed overlapping spheres was used to represent the soil solids, the pores being what remains. Various simulated porosities and average sphere radii produced pore networks which resembled those in real soil aggregates. Our diffusion simulations gave three results: steady-state flux, time delay and rate of increase of flux. The porosity and sphere size were varied to investigate their effects on these diffusion properties. Results were comparable with those from experimental work. Further analysis allowed us to express the geometry of pore simulations in terms of average pore path length and connectivity. Evidence of non-Fickian behaviour was obtained, particularly in the early stages of the simulated diffusion.