Mercury intrusion porosimetry and centrifuge methods for extended-range retention curves of soil and porous rock samples

The water retention function is essential for modeling flow and transport in porous media. Its experimental determination is still challenging because each of the standard methods is limited to partial moisture ranges. The pore-size distribution (PSD) obtained by the mercury intrusion porosimetry (MIP) may be used as a unifying property that spans across the individual ranges of retention properties obtained with standard methods. This study compares the MIP and quasi-steady centrifuge (QSC) methods with standard ones (suction table, evaporation, and dewpoint potentiameter) to determine the retention curves of subsoil clods and calcareous rocks over most of the moisture range. The selected soils, having a relatively rigid structure compared with other soils, are more similar to the rocks even if there is a non-negligible difference in terms of mechanical strength. The QSC, developed for rock samples, was tested for soil to see if the method is also applicable for mechanically less stable media. The porosity characteristics of soil and rock samples showed bi- and trimodal PSDs. The single MIP test allowed describing the mercury retention curve (MRC) for most of the volumetric mercury content range. The MRCs could be used to fill the gaps in the retention curves that occur with the standard retention procedure when switching from one measurement range to the other. The MIP and QSC methods proved to be relatively fast and reliable for measuring a wider range of the retention curve. However, the application of QSC method to soil samples is limited by effects of compaction due to centrifugal force.