Numerical assessment of soil water dynamics and penetration resistance in the presence of compacted layers

Soil compaction commonly occurs as compacted layers with reduced permeability, which can significantly affect water flow and retention throughout the soil profile, shortening drainage time and altering soil penetration resistance. The objective of this study was to investigate the impact of a compacted layer on soil water flow and penetration resistance using numerical modeling based on Richards’ equation implemented in COMSOL Multiphysics. A two-dimensional problem representing a soil profile was constructed with and without the presence of a compacted layer. The effect of compaction was examined by systematically increasing both the thickness of the compacted layer and the degree of compaction. Model parameterization was based on literature data for a clayey soil, including soil water retention curves, saturated hydraulic conductivity, and parameters describing soil penetration resistance. These parameters were used to numerically solve Richards’ equation for drainage from saturated conditions and to assess the influence of compacted layers on the temporal evolution of penetration resistance as a function of drainage time up to 10 days free drainage. The results showed that the presence of a compacted layer caused only minor changes in matric potential along the soil profile over time. The dominant factor controlling changes in penetration resistance in the simulations was the degree of compaction itself, as the lower permeability of more compacted layers promoted greater water retention in their vicinity, thereby alleviating soil penetration resistance. In conclusion, numerical simulations showed that compacted layers induced only minor changes in soil matric potential during drainage for actual compaction degree conditions. The degree of compaction was the primary factor controlling the temporal evolution of soil penetration resistance, outweighing the effect of layer thickness. Lower permeability in highly compacted layers promoted greater local water retention, which mitigated increases in penetration resistance over time. The scenario examined in this study should be extended to soils with varying textures and permeability in order to assess the broader applicability of these conclusions.