A new water retention model that considers pore non-uniformity and evolution of pore size distribution

Pore size distribution (PSD), which is usually measured using mercury intrusion porosimetry (MIP) tests, is often used to predict the water retention curve (WRC) of unsaturated soil. Existing models generally predict the drying path of the WRC only because the intrusion of non-wetting mercury in MIP tests is equivalent to air entry during drying. Moreover, the PSD changes under hydro-mechanical loads, which has a significant effect on water retention behaviour. In this study, a new model is developed to predict both the main drying and wetting paths of WRCs. Based on a single PSD at reference stress and suction conditions, we quantified the influence of pore non-uniformity on MIP test results and the main drying and wetting paths of WRCs using the new model. From the reference PSD, we determined variation in the PSD with stress and suction and incorporated this variation into modelling of the WRC. The newly developed model was applied to simulate the PSD variation and the hysteretic WRC of different soils. Based on the results, it is evident that the new model is able to capture the evolution of the PSD during drying, wetting and compression. Moreover, the main drying and wetting paths of WRCs of unsaturated soil were closely predicted.