LABORATORY TESTS OF A THEORY OF FINGERING DURING INFILTRATION INTO LAYERED SOILS

When the conductivity of a coarse-textured sublayer at its effective water-entry suction is greater than the rate of transmission through a finer-textured top layer, the flow velocity increases across the interlayer plane. A spatially-distributed flow field in the top layer will tend to constrict, forming spatially separated streams (fingers) in the sublayer. Ponded infiltration experiments were conducted in air-dry sands. The hydraulic properties were determined by equilibrium capillary rise, parameter estimation, and horizontal absorption experiments. Measurements of flux and suction at the inter-layer plane revealed that the effective water-entry suction is characteristic of the predominant pore size in the sublayer and can be predicted from its median particle size (r2 = 0.99). Predictions regarding the onset of fingering and the wetted fractional volume of fingers were validated. -from Authors