This study systematically investigated the pore structure response of kaolin and illite/smectite mixed-layer rich clay in a reconstituted state to one-dimensional (1D) compression by first performing oedometer tests on saturated clay slurries, followed by characterising their pore structure using multi-scale characterisation techniques, with the primary objective of advancing the current understanding of the microstructural mechanisms underlying the macroscopic deformation of such clays. Under 1D loading, the volume reduction observed at the macro level essentially represented the macroscopic manifestation of changes in inter-aggregate porosity at the pore scale. It was the inter-particle pores that were compressed, despite the interlayer pores remaining stable. Two distinct pore collapse mechanisms were identified: kaolin exhibited a progressive collapse of particular larger pore population in an ordered manner, whereas illite/smectite mixed-layer rich clay demonstrated overall compression of inter-aggregate pores. Accordingly, mathematical relationships between the porosity and compressibility parameters for these two soils were proposed, with the two exhibiting opposite trends arising from their distinct microstructural features. Approaching from the unique perspective of pore structure, quantitative analysis of pore orientation and morphology on the vertical and horizontal planes demonstrated some progressively increasing anisotropy during compression. These findings provide important insights into porescale mechanisms governing clay compression behaviour and enrich the limited microporosity database in soil mechanics.

The salt concentration of the pore solution can alter the micro-pore and particle structure of soil, thereby affecting its engineering properties. To investigate the compression characteristics of marine soil under different salt concentrations, one-dimensional compression and SEM scanning tests were conducted on marine reconstituted clay from the Yellow Sea with varying NaCl concentrations (0-5%). The effects of NaCl concentration on the compression characteristics and microstructure of marine sedimentary clay were analyzed. The results indicate that: (1) Compressibility increases up to a NaCl concentration of 2.5%, after which it declines. At 2.5% NaCl threshold concentration, the coefficient of compression, compressibility index, and consolidation coefficient reach their peak values, and the response becomes more pronounced with increasing compression pressure. During the secondary compression stage, as pore water is expelled, the impact of NaCl concentration on compressibility diminishes, while the rebound characteristics remain unaffected by NaCl concentration; (2) SEM analysis reveals that at a NaCl threshold concentration of 2.5%, the pore fractal dimension, particle fractal dimension, pore anisotropy, and particle anisotropy reach their maximum values, with the most complex shape and pores and particles aligning in the same direction. When the concentration is less than 2.5%, the soil exhibits narrow pores and rounded particles upon compression. When the concentration exceeds 2.5%, the microstructure changes in the opposite direction, confirming the particle rearrangement mechanism driven by surface contact under moderate salinity. At the threshold concentration of 2.5%, a balance between electrostatic forces and attractive forces enables stable surface-to-surface contacts, maximizing compressibility. The findings of this study provide valuable references for the foundation design of marine geotechnical engineering in specific sea areas, thereby enhancing the safety and reliability of related projects.

Soil-rock mixtures are extensively used in geotechnical engineering applications, such as embankment construction, dam engineering, and slope reinforcement, where their compressive deformation characteristics play a crucial role in influencing the stability and settlement behavior of these structures. This study investigates how variations in rock content (W), effective stress (sigma v) and fine-grained soil properties (quartz sand and silty red clay) affect the one-dimensional compression behavior of soil-rock mixtures. Key compression parameters, including the compression index C c and the secondary compression index C a, were obtained and analyzed through one-dimensional consolidation tests to assess the deformation characteristics of these mixtures. Results show that under the same effective stress (sigma v), both the C c and C a exhibit different trends with W, depending on the properties of the fine-grained soil. Soil-rock mixtures with silty red clay demonstrate more pronounced secondary consolidation effects at low rock content, whereas mixtures with quartz sand display weaker secondary consolidation overall. The significantly lower C a /C c values in the quartz sand mixtures suggest that secondary settlement is much smaller in these mixtures compared to those containing silty red clay.

Since hydraulic conductivity significantly influences the compression and deformation characteristics of granular terrains, this study examines the variations in permeability (k20) of granular soils under one-dimensional compression. Two uniformly graded calcareous soil samples were tested: one with grain sizes of 9.50-12.70 mm, and another of 4.75-9.50 mm. Both samples were subjected to one-dimensional compression and constanthead permeability tests. Key soil properties affecting permeability (k20), including absorption (n), specific surface area (Ss), relative density (Dr), void ratio (e), uniformity coefficient (Cu), effective grain size (d10), and mean grain size (d50), were analyzed. The virgin compression line (VCL) of the soil samples was identified within an oedometric stress (sigma VCL) range of 4.00-14.00 MPa, where the rate of change in soil properties affecting permeability was most pronounced. As oedometric stress increased, the instantaneous absorption (ni) of the soil samples increased linearly, with a slope (alpha n) of 0.055-0.061. Similarly, the instantaneous specific surface area (Ss,i) of the soil samples increased linearly, with a slope (alpha s) of 1.229-1.388. In addition, practical equations were developed to predict the instantaneous relative density (Dr,i), instantaneous grain size distribution curve, and instantaneous permeability (k20,i) of granular soils under one-dimensional compression.