Application of the Green-Ampt model for infiltration into layered soils

Using the Green-Ampt model for layered soils, a theoretical method is proposed to estimate the layers' hydraulic parameters based on infiltration test data. To evaluate the proposed method and to investigate the effect of the layers' permeability on infiltration, constant head infiltration tests were conducted on six different two-layered soil columns. When the upper layer was more permeable than the lower layer, piston flow was observed in both layers, and the air-filled volume fraction of the lower layer was nearly equal to the observed values in homogenous soils. In this situation, the layers' hydraulic parameters can be estimated from the proposed method. When the lower layer was more permeable than the upper layer, piston flow with a large air-filled volume fraction was observed in the lower layer. When the lower layer was significantly more permeable with an approximately zero wetting front matric head, preferential flows or instability in the wetting front was observed in the lower layer. In two-layered soils with a more permeable layer below a low permeable layer, the hydraulic conductivity of the lower layer cannot be estimated based on infiltration test data. (C) 2015 Elsevier B.V. All rights reserved.