Abstract
<title>Abstract</title> <p>This study investigates how one-dimensional consolidation, swelling, and overconsolidation alter pore morphology in two natural clays of contrasting mineralogy, an illite-dominant Loess clay and an interstratified illite-smectite Lucera clay, tested under both deionised and saline pore fluid conditions. Three principal questions are addressed: (i) how pore size distributions and morphological descriptors evolve under loading and unloading; (ii) whether pore size and shape recover fully upon swelling, quantified through a pore shape recovery ratio (PRR); and (iii) whether pore fluid chemistry systematically alters pore morphology and its stress-dependent evolution across contrasting clay mineralogies. Reconstituted specimens were consolidated from 100 to 3200 kPa and swelled to overconsolidation ratios up to 1280 in both deionised and saline conditions. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were applied to freeze-dried specimens to characterise pore size distributions and morphological descriptors including Feret diameter, circularity, aspect ratio, solidity, and pore orientation angle. Pore size distributions are monomodal throughout the tested stress range in both fluid environments. Saline specimens exhibit systematically smaller mean Feret diameters than deionised specimens at equivalent stress levels in both clays, consistent with double-layer compression reducing inter-particle repulsion in the presence of dissolved ions. Swelling produces partial, non-symmetrical pore recovery in both fluid conditions: Feret diameter recovers fully or exceeds the normally consolidated reference (PRR = 1.00-1.35 in deionised; 0.98-1.38 in saline), whereas circularity and aspect ratio show incomplete recovery (PRR = 0.56-1.57), increasing in severity with prior consolidation stress regardless of pore fluid environment. Overconsolidated specimens retain smaller, more elongated, and less circular pores than normally consolidated specimens at equivalent void ratios in both conditions, captured by logarithmic descriptor-OCR relationships. The grading parameter Cₚ of pore diameter, circularity, and aspect ratio follows power-law relationships with vertical effective stress for both clays and both fluid conditions.</p>