Petrological and geotechnical studies of lateritic soils in the locality of Ngaoundal (Adamawa-Cameroon): implication in road construction

Abstract

The aim of this study is to carry out a petrological and geotechnical study of the lateritic soils of Ngaoundal (Adamawa-Cameroon). Hence, geotechnical identification, X-ray difractometry, and chemical analysis (XRF) were used to characterize soils. Field investigations show that the average thickness of the lateritic layers is 1.3 m; the soils encountered are nodular with a silty/clay matrix. The dominant color is dark brown (7.5YR 5/6) with a lumpy structure and silty or clayey texture. Mineralogical analysis (XRD) and chemical data (XRF) show that these materials are made up of quartz (38.27%), goethite (13.98%), gibbsite (10.59%), kaolinite (8.62%), hematite (7.88%), magnetite (8.38%), anatase, and boehmite. These soils are silico-ferrugino-aluminous. Their silica/sesquioxide ratios correspond to those of true laterites. X-ray diffraction analysis of the soil samples revealed the absence of swelling clays. Geotechnical analyses indicate that these soils have specific weights between 2.580 and 2.648 g/cm³. The liquidity limits show an average of 54.5%, with an average plasticity index of 29.73%. According to the (HRB) classification, these soils belong to the class of silty/clayey gravels and sands known as A-2–7. The values for maximum dry density and optimum water content range from 2.040 to 2.188 g/cm³ and from 9.5 to 13.6% respectively. The CBR bearing capacity index shows values ranging from 78.0 to 95.1%, which proves that these materials belong to bearing capacity class S5. The geological and geotechnical data confirm that the Ngaoundal materials are suitable for road construction (sub-base and base layers).