Relationships between Shear Strength Parameters with Mineralogy and Index Properties of Compacted, Unsaturated Soils

The objective of this study is to assess the influences of soil index properties, swelling parameters, and soil mineralogy on unsaturated shear strength parameters (ϕ‘, ϕ^b, c‘) of compacted expansive soils. The laboratory tests include the grain size distribution, specific gravity (Gs), Atterberg limits, swelling potential, X-ray diffraction, modified Proctor compaction, soil suction, and triaxial testing. MINITAB 19 statistical analysis software generates the tri-dimensional surface graphs. The values ϕ‘, ϕ^b, and c‘ are majorly influenced by water (%), Gs, and clay (%). ϕ‘ shows a strong correlation with free swell ratio (FSR), free swell index (FSI), and void ratio. ϕ^b demonstrates a strong relationship with liquid limit, plasticity index, and γ_d (dry unit weight). ϕ‘ and c‘ portray a moderate relationship with liquid limit, plasticity limit, and γ_d. ϕ‘ exhibits a moderate correlation with smectite (%) and plagioclase (%). ϕ^b describes a strong relationship with smectite (%) and a moderate correlation with plagioclase and K-feldspar (%). c‘ depicts a moderate correlation with smectite (%), K-feldspar (%), and plagioclase (%). The matric suction controls the behaviour of unsaturated soils. Nonetheless, the influences of soil index properties, swelling potential, and mineralogy on shear strength are not marginal. These findings provide a good insight into the behaviour of unsaturated expansive soils and contribute to enhancing geotechnical modelling.