Geotechnical and Mineralogical Evaluation of Lateritic Soils to Access Their Suit ability for Engineering Construction Works: A Case Study of Some Selected Re sidual Soils in Parts of the Southwestern Nigeria

Abstract

This study investigate the geotechnical and mineralogical properties of differently sourced lateritic soils in order to determine their suitability for engineering construction purposes. In addition, attempts were made to establish the relationships between mineralogy and some geotechnical/engineering properties. Five lateritic soil samples derived from quartzite, mica schist, amphibolite, sandstone and migmatite-gneiss in parts of the southwestern Nigeria were collected in the field for geotechnical tests as well as determine their mineralogical compositions using x-ray diffraction (XRD). Result from grain size analysis shows that the soils are generally fine to medium grained consisting mainly of clayey silty sand. The Atterberg consistency limits revealed that the soils contain inorganic clay of low to intermediate plasticity, with linear shrinkage limit between 7% and 10%, indicating medium shrink potential. Based on the Skempton’s activity chart, the soil can be classified as active to moderately active soils. The maximum dry density values of the samples at standard proctor energy of compaction range from about 1.46 g/cm3 to 1.96 g/cm3, while those obtained at modified proctor energy vary between 1.57 g/cm3 and 2.09 g/cm3. The shear strength tests give angle of internal friction between 31o and 33o and cohesion values ranging between 59kPa and 70kPa for the standard and modified proctor compaction, respectively. These values indicate that the soils will have high bearing capacity and could support a moderately steep slope. The coefficient of permeability of the soils is low with k ranging from 0.7 x 10-8 m/sec to 8.79 x 10-8 m/s, which falls within the range considered to be impermeable. The soaked and unsoaked California Bearing Ratio (CBR) values vary from about 1% up to 6%. Based on the geotechnical analysis, the soils can be used as liners in landfill system, fill materials in embankments and earthfill dam construction as well as subgrade and fill materials for road pavement in highway construction. The mineralogical analysis showed that the soils are mostly composed of illite, kaolinite, quartz, feldspar, hematite and goethite