Abstract:

Kaolinitic clay soils from Ikere, Isan, and Ijero in Ekiti State, southwestern Nigeria, were investigated to evaluate their geotechnical and geochemical characteristics relevant for stabilisation requirements and engineering applications. Representative samples obtained at multiple depths were subjected to index testing, direct shear, permeability, dynamic cone penetration tests, and microstructural analysis using SEM–EDS. The soils exhibit relatively uniform index properties, with clay contents of approximately 48%, but show weak strength characteristics, including low cohesion and moderate friction angles, alongside low permeability. Despite similar bulk properties, notable spatial variability in engineering performance was observed. Ikere clay demonstrated high bearing capacity at depth, whereas Ijero and Isan clays exhibited weak subgrade conditions near the surface. Microstructural and geochemical analyses confirm kaolinite dominance, with variations in Si/Al ratios and organic content influencing pore structure, moisture retention, and strength behaviour. Weak correlations between bulk composition and strength parameters highlight the governing role of soil fabric and microstructure rather than mineralogical composition alone. Based on these findings, site-specific stabilisation strategies are proposed: lime treatment for Ijero clay, compaction-based improvement for Ikere clay, and combined lime–cement stabilisation for Isan clay to mitigate drainage and settlement risks. This study provides new regional data and demonstrates the importance of integrating microstructural analysis with geotechnical testing to improve subgrade design and enhance infrastructure durability in tropical lateritic environments.