Field Measurement of Rainfall Infiltration in Capillary Barrier of Soil and Determination of Its Divergence Length

Abstract

Capillary barrier is the simple soil layer system which is composed of the fine soil (sand) layer underlain by the coarse soil (gravel) layer. The capillary barrier of soil was constructed in sand slope, and volumetric moisture contents in the soil were successfully measured together with precipitations for about four months. Soil moisture changes in the gravel layer were well compared those in the sand layer to confirm a practically excellent divergence of infiltration water along the tilted interface between the sand and gravel layers. The field measurement detected a possible percolation or breakthrough of water flow along the interface into the gravel layer. A divergence length of the capillary barrier where the percolation or breakthrough of water flow into the gravel layer occurred was estimated using soil properties determined by laboratory tests and structural configuration of the capillary barrier of soil. A fairly good correspondence of the divergence length between the observation and the estimation demonstrated a practical effectiveness of the equation previously published to calculate the divergence length. This should lead the capillary barrier of soil to an alternative and effective measure for soil slope stability because the divergence length determines the soil layer structure as well as the soil materials employed in the construction.