The effect of column diameter on the infiltration behaviour of a swelling soil

Abstract

The interaction between soil particles and the retaining wall of a column on the infiltration behaviour of a swelling soil was studied for six column diameters and three crumb sizes. The infiltration rate, rate of advance of the wetting front, and relative swelling, were found to be significantly affected by the column diameter, such that the smaller the diameter, the slower the infiltration rate and the rate of advance of the front and the smaller the swelling. In addition, an effect due to the soil fraction size was significant but much less important than column diameter. This secondary effect is attributed to the differential slaking of soil crumbs, greater slaking depth being associated with larger size fractions for a given column diameter. The surface layer during infiltration has a structure quite different from that associated with original crumb structure and the layers below the surface. This layer, in which both swelling and slaking have occurred, controls infiltration, and the entry of water into the profile is similar to that observed for a two-layered stratified system. It is concluded that the minimum column diameter for studies concerning water movement through swelling materials should be no less than 10 cm.