Physico-chemical effects on collapse behaviour of compacted red soil

Physico-chemical effects assume significance in geoenvironmental engineering applications where compacted soils and natural soil deposits interact with chemical contaminants. The physico-chemical interactions occur at the microstructural level and affect the macrostructure and thus the volume change behaviour. This paper brings out the physico-chemical effects on the compressibility and collapse behaviour of compacted red soil. The physico-chemical effects were induced by using different fluids for specimen preparation and inundation. Salinisation of compacted specimens prepared with distilled water induces outward osmotic flow and causes induced osmotic consolidation. In addition, the diffusion of saline solutions into the compacted specimens leads to microstructural contractions at the clay particle level and results in an increase in the irreversible macrostructural strains. Consequently, the macrostructure experiences plastic hardening and this results in greater collapse strains. Scanning electron micrographs showed an increase in the size of macrovoids (loose macrostructure) with the increase in pore fluid osmotic suction owing to the microstructural contractions. Therefore, this paper also provides an insight into the behaviour of specimens prepared with saline solutions with respect to the initial loading–collapse (LC) curves and collapse behaviour when subjected to inward osmotic flow and no osmotic flow conditions. The specimens prepared with saline solutions yielded at lower vertical stress in comparison with the specimens prepared with distilled water, and the elastic response of the compacted soil was found to be independent of both matric and pore fluid osmotic suctions. The osmotic swelling, which occurs owing to dilution of pore fluid at the microstructural level, resulted in slightly lower collapse potentials in specimens subjected to inward osmotic flow condition in comparison with the no osmotic flow condition.