Optimizing lime stabilization of organic-rich marine clay with sodium chloride

Cochin marine clay found along the coastal belt of Kerala pose significant geotechnical challenges due to their high compressibility, low shear strength, and substantial organic content. Lime stabilization, a widely used soil improvement technique, often fails to deliver long-term strength enhancements in such soils because organic matter inhibits pozzolanic reactions and reduces pH over time. Therefore, chemical additives should be introduced while applying lime stabilization in those areas. In this paper, an attempt has been made to examine the effect of NaCl on lime-stabilized Cochin marine clay over an extended period of 120 days unlike previous studies that focused on CaCl₂ or MgCl₂ additives and shorter curing durations. Soil specimens were prepared with 6% lime and varying NaCl concentrations (2.5%, 5%, and 10%) and subjected to unconfined compressive strength (UCS) tests after curing periods of 0, 7, 30, 60, and 120 days. Scanning electron microscopy (SEM) was conducted after 120 days to assess microstructural changes. Results revealed that adding 5% NaCl significantly enhanced strength, achieving over a sevenfold UCS increase after 120 days compared to lime-only treated samples. Cementation improved due to formation of calcium silicate hydrate and calcium aluminate hydrate. NaCl enhanced the ion exchange by increasing the availability of Ca²⁺ ions and reducing clay particle repulsion through double-layer compression. Whereas, excess salt (10%) led to dispersion and reduced long-term strength. The study concludes that sodium chloride, at an optimized concentration, can effectively mitigate the limitations of lime stabilization in coastal areas with organic-rich marine clays.