Transport in Porous Media, Vol.71, No.2, 147-159, 2008
Steady water flow through unsaturated aggregated porous materials
The three-dimensional steady water flow through unsaturated aggregated porous materials composed of simple cubic open packed and tetrahedral close packed assemblies of uniform porous spheres is investigated with electric analogues and numerical computations. Water around the spheres is considered to be discontinuous with flow restricted through isolated annular water lenses held by surface tension forces around the contact points between spheres. It is found that the conductance of individual spheres depends only on the size of the water lenses and is independent of the radius of the sphere. For a simple cubic packing the conductance for small lens radii is given by Weber's formula for flow from an electrified disc into an infinite medium. It follows that the bulk hydraulic conductivity of these assemblies of porous spheres is also independent of aggregate size over a range of water contents. This independence is also shown in measurements of hydraulic conductivity of aggregates of diatomaceous earth that show a convergence to a single relationship between conductivity and water content when there is no longer continuity of water in the macropore space. The effect of the three-dimensional flow through aggregates on solute leaching is demonstrated by considering the numerical results of the stream-tube pattern in a sphere.
Keywords:steady water flow;unsaturated aggregated porous materials;hydraulic conductivity;spherical aggregates