3-DIMENSIONAL ANALYSIS OF INFILTRATION FROM THE DISC INFILTROMETER .1. A CAPILLARY-BASED THEORY

The hydraulic properties of an unsaturated homogenous and isotropic so il can be obtained from the unconfined flux out of a disc infiltromete r into the soil over the depth of wetting. The disc infiltrometer is b ecoming increasingly popular, but methods of analysis have generally r elied on the restrictive assumptions of one-dimensional flow at early times or quasi-steady state flow at large times. We provide an approxi mate analytical expression for three-dimensional unsteady, unconfined flow out of a disc infiltrometer, and this includes the geometric effe ct of the circular source but ignores gravity. This physically based s olution is tested against data obtained from laboratory experiments on repacked material. The results illustrate that the difference between three-dimensional and one-dimensional flow is linear with time.