The experimental results of the present study on compacted expansive clay illustrate that matric suction increases with the increase in pore fluid osmotic suction due to changes in soil structure. Scanning electron micrographs show that particle stacking (aggregations) increases with increase in pore fluid osmotic suction and cation valence due to reduction in diffuse double layer thickness, and thus results in a reduction in micro pore size with a corresponding increase in macro pore size. At a given water content, the macro pore degree of saturation reduces with the increase in osmotic suction owing to the increase in macro pore size and leads to an increase in matric suction, as the matric suction is characteristic of the macro pore and the degree of saturation of the macro pore. The matric, osmotic and total suction measurements using the filter paper method also confirm that the matric and osmotic suction components are additive. This demonstrates that the method of obtaining matric suction from the difference between total suction and pore fluid osmotic suction determined using non-contact filter papers is reliable.
The present study examines the effect of inflow of sodium chloride solutions on the swell–compression behaviour of compacted expansive clays under a range of external loads. Inflow of sodium chloride solutions reduced the swell magnitudes and pressures and even caused the compacted clay specimens to experience compressive strains in oedometer tests. The axial strain difference of specimens inundated with sodium chloride solutions and distilled water at a constant effective stress predicted the osmotic consolidation strains of a saturated clay specimen from an increase in osmotic suction in the pore fluid. Specimens exposed to larger osmotic suction gradients (Δπ) are predicted to experience larger osmotic consolidation strains. The predicted osmotic consolidation strains exceeded the experimental osmotic consolidation strains. The free-swell and load method and the swell under load procedure predicted different swell pressures owing to differences in strain contributions at the microstructure and macrostructure levels. The increase in osmotic suction in pore water apparently acts as an equivalent net stress (ρπ) that favours a reduction in swell potential of the compacted clay specimens due to a reduction in reversible swelling strains from an increase in net stress and irreversible macrostructural component that decreases because the distance of the stress point to the load–collapse (LC) curve decreases.Key words: compacted clays, chemical gradients, osmotic consolidation, suction, swell.
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