Investigation of the Impact of Tropical Red Clay Soils' Mineralogical Composition on their Physical and Mechanical Properties– a Case Study Ruaka – Kenya

Residual soils covering large areas of the earth have been chiefly discovered in the last 30 years in most volcanic tropical and subtropical countries. Understanding their behaviour is essential for various infrastructure developments.

The physical and mechanical properties of the soils are affected by their mineralogical composition. There is a need to determine the mineralogical composition of the soils and investigate the impact on properties. This paper presents the results of a laboratory study conducted on red clay soil from Ruaka, a suburb in Kenya, to investigate the effect of mineral and chemical composition on the soil’s physical and mechanical properties. Disturbed and undisturbed samples were subjected to different tests such as Atterberg limits, soil classification, consolidation test, X-ray fluorescence, X-ray diffraction and petrology test based on the British Standard soil classification system (1377-1994). The soils were classified as clay with high plasticity, and high clay content varied between 59-79% resulting in mechanical instability of the soil in this site.

The mineral and chemical analysis indicated the formation of unique minerals like Halloysite, Quartz, Kaolinite, and Mica, which influenced the geotechnical properties of clay. The index properties of clay recorded high values; the moisture content and plastic limit varied between 37- 46% with a slight increase as depth increased; the liquid limit varied between 63-68% with increased depth.

The average value of maximum dry density was reported as around 1247 kg/m3 with high optimum moisture content, reaching 35.5%. Besides that, the soil had a high void ratio of 1.145 to 1.63, which increased the permeability of the clay to 1.223E-5 cm/s. The properties of red clay soils in more than ten tropical regions in Kenya compared with the soil under study are also presented in this paper.