Impact of Soil Geochemistry on the Stability of Engineering Structures in the Tropics

Abstract

Stability and durability response of expansive soils are important in engineering structures, hence the need to examine its mineralogy and geochemical composition. Ten samples were collected at varied locations in south eastern Nigeria from devastated infrastructures and were investigated using XRD, XRF and relevant preliminary tests (particle size distribution and Atterberg limits) in consonance with American Society for Testing and Material (ASTM) Standards. Major elements detected were Si, Al, Fe, K, Ti, Ca, Ag, Li, Ba and Cr, while oxides of Al2O3 and SiO2 from different sources (clay minerals in clay size particles and quartz mineral in sand fraction respectively) influenced the soil engineering behavior. Result showed that Fe, Ca, Li, Ba, Ag, Zn and Cr could substitute for Al. However, when present as either substitution for Al or as adsorption on the clay minerals, soil swelling potential is enhanced but if it exists as components of the cementing material such as ZnO, MnO and CaCO3, swelling potential diminishes. Ratios of the oxides indicate that the soils in our study area contain swelling clay minerals (montmorillonite, illite and kaolinite) in varied proportion which corresponds with the XRD results. Values of liquid limit, plasticity index and free swell were 60.7, 41.3 and 82.3% respectively, indicating medium to high swelling potentials, capable of causing serious engineering problems on wetting at construction sites.

Keywords: Swelling potential, Clay minerals, Substitution, Correlation, Heavy metals, Active elements