Suction-driven evolution of pore structure heterogeneity and its influence on water retention hysteresis

Intrusion and extrusion cyclic mercury intrusion porosimetry (IEC-MIP) partitions pore bodies and pore throats and quantifies ink-bottle controlled heterogeneity. Interpretation for deformable clays on the drying path remains uncertain because matric suction induces shrinkage that reshapes pore bodies and throats. This study combines suction controlled drying with IEC-MIP to quantify suction driven evolution of heterogeneity and its implication for soil water retention curve (SWRC) hysteresis. Reconstituted specimens (RS) and compacted specimens (CS) of Nanyang clay were prepared at two initial void ratios and three suction levels. Void ratio reduction is dominated by pore body contraction, with pore body volume decreasing by about 75% across the studied suction range, while throat volume changes remain below 25%. A heterogeneity factor h derived from intrusion and extrusion volumes, where lower h indicates a stronger ink-bottle effect, increases with suction and mechanical compression, indicating progressive homogenization. RS and CS show pore size dependent differences, with h differing by about 20 to 30% for pore diameters of about 30 to 500 nm. If shrinkage is ignored in IEC-MIP interpretation, h underestimates the SWRC derived hysteresis index by up to 40%, whereas incorporating suction effects yields consistent bounds across suctions.