Effects of pore structure on the hysteretic water retention behaviour of silty sand at different stresses

It is well-recognised that stress can greatly affect the pore characteristics of unsaturated soil, such as pore size distribution (PSD) and pore shape (PS). So far, the effects of PSD and PS on the drying and wetting water retention curve at different stresses have not been well understood. To fill the knowledge gap, eight water retention tests were carried out to evaluate the effects of PSD and PS on hysteretic water retention behaviour at different stresses. Soil specimens purposely prepared at two compaction water contents and two initial void ratios were subjected to drying and wetting under two different net stresses (0 and 50 kPa). Moreover, mercury intrusion porosimetry (MIP) and micro-X-ray computed tomography (µ-XCT) were used to quantify the microstructure of specimens. The results showed an important role of pore structure in the hysteretic SDSWRCs. Compared to the specimens prepared on the dry side, specimens compacted on the wet side of the optimum are highly aggregated, possessing a lower water retention ability but a higher degree of hysteresis. The higher hysteresis observed in the highly aggregated specimens can be explained by the irregular-shaped pore characteristics observed in µ-XCT tests.