Determining the influence of stones on hydraulic conductivity of saturated soils using numerical method

Abstract

Mountainous soils usually contain a large number of rock fragments (particle diameter > 2 mm), which influence soil hydraulic and retention properties. Data characterizing the properties of these soils usually describe only the fine earth (particle diameter < 2 mm). To quantitatively describe soil water movement in stony soils, their most important characteristic, i.e., the effective saturated hydraulic conductivity ( K se ), must be known. The objective of this study was to use a numerical method for estimating the saturated soil hydraulic conductivity that depends on relative stone content (stoniness), and sizes and shapes of stony parts. The method is based on a numerical version of the classical experiment of Darcy. The steady-state water flow under a unit hydraulic gradient through hypothetical soils containing stones was simulated using the two-dimensional simulation model HYDRUS-2D. Four soil textural types were considered. Special attention was paid to the moraine soil from the FIRE site in High Tatras. A relationship between the relative saturated hydraulic conductivity, K r , and the relative stone content, R v , was derived. K r ( R v ) function is decreasing slower for larger stones. Numerical results were used to propose an empirical equation to estimate K r of soils containing rock fragments of a spherical shape of various diameters.