Soil bearing parameters and settlement prediction using CPT data in Southwestern Nigeria / Olumuyiwa Olusola Falawo, Abayomi Solomon Daramola and William Kunle Olabisi

The study was aimed at deriving important soil parameters relevant to civil engineering construction in schistose quartzite/quartzite dominated soil of RUGIPO, Ondo State, Nigeria, using cone penetration test (CPT). Key engineering parameters’ findings revealed a high degree of overlapping values within the two geological formations. However, both soils are very dense, stiff/hard soil, with a high dominance of coarse particles (sand) over the finer soil matrix (silt). Soil from quartzite has better bearing pressure (avg. 405 kN m−2) than schistose quartzite (324 kN m−2), even above the regional average of 346 kN m−2. The total settlement of the soils (avg. 26 mm), for structural loads of 100–200 kN and foundation width of 1–2 m, gave values less than permissible limits for clay (100 mm) and sand (50 mm) dominated soil, with schistose and quartzite displaying an average of 27 and 24 mm. The CPT material index with a regional average of 2.40, with schistose quartzite and quartzite showing average values of 2.39 and 2.42, and average soil permeability of 6.19 × 10-7 m s−1 and 4.498 × 10-7 m s−1, respectively. The soils have a mean CBR value of 38%, with the CBR of schistose quartzite (35%) less than that of quartzite (42%). The regression models of all the parameters generally gave positive correlation coefficients, especially CBR and Mo (0.6522), RD and CBR (0.6536), Su and qc (0.9849). The practical implications of the result indicated that both soils are competent for construction (pavement, foundation, and embankment construction) in both geological formations.