An innovative experimental device to quantify the water relative permeability and in situ water retention curves of unconsolidated porous media

Accurate determination of water relative permeability ( k rw ) is essential for modelling flow in porous media. Traditional methods often rely on bulk averaging and assumed unit hydraulic gradients, which limit spatial resolution and introduce uncertainties. This study presents a novel experimental column setup that integrates a PICO TDR probe for in situ water content measurement and dual pressure transducers for direct pressure gradient monitoring under steady-state flow conditions. Experiments were conducted on two water-wet quartz sands (P100 and P2040), which differed in grain sizes and porosities. A stepwise drainage and imbibition protocol enabled the derivation of both water retention curves and water relative permeability ( k rw – S w ) curves, using Darcy’s law and matching-point normalization. Initial saturation was achieved through upward imbibition using distilled water, preceded by a nitrogen injection to minimize air entrapment and accurately determine porosity. Each experiment was repeated under identical conditions to verify the reproducibility of the results. Results show minimal hysteresis between drainage and imbibition curves and excellent agreement with the Mualem–van Genuchten predicted k rw , using parameters independently derived from the water retention curves. The approach demonstrates high reproducibility and predictive accuracy, providing a strong platform for future studies involving pore-scale simulations, wettability alteration, or hysteresis modelling.