Hydraulic Conductivity and Water Retention Functions of Porous Rock and Glacial Till Soil: Quasi-Steady Centrifuge versus Evaporation Methods

Experimental laboratory measurements of the hydraulic conductivity and the water retention functions have a crucial role in describing the solid matrix-water dynamics. However, the direct determination of the hydraulic conductivity, K, as a function of the pressure head, h, is still difficult. It is often estimated indirectly from the water retention curve, which relates the water content, θ, to h, or obtained by using pedotransfer functions or by field data of pumping tests. In this study the unsaturated hydraulic conductivity values of carbonate porous rocks and soil clods were measured by means of evaporation, Quasi-Steady Centrifuge (QSC) and double-membrane steady-through flow methods. Water retention curves were obtained by using the evaporation, QSC, suction table, Mercury Intrusion Porosimetry (MIP) and pressure chambers methods. Samples belonging to two rock lithotypes collected in southern Italy and to two soil clods coming from northeastern Germany were tested. The data were fitted to the unimodal and bimodal functions of van Genuchten and the Peters-Durner-Iden models by using the LABROS SoilView Analysis software. The bimodal functions better described the experimental data of both the studied rocks and soils. The soil compaction during the centrifuge runs performed by applying the QSC method, corroborated by changed values of bulk density, porosity, tortuosity, and pore connectivity after the runs, confirms that this method is not suitable to non-rigid media. The results confirm that the QSC method allows measuring the unsaturated hydraulic conductivity values for rock samples. The larger range of experimental hydraulic conductivity values helps to improve the fitting and obtain the more accurate of the hydraulic conductivity function to better describe the unsaturated rock-soil-water dynamics.