Geotechnical Evaluation of Reddish Brown Tropical Soils

Laboratory investigations were carried out on reddish brown tropical soils from Moniya, Ibadan Southwestern Nigeria to determine the basic unconfined compressive strength of the soil samples which is an important factor to be considered when considering materials as liners in waste containment structure. Clay mineralogy, major element geochemical analyses were carried out by means of X-ray diffractometry and X-ray fluorescence spectrometry respectively. The engineering tests such as sieve size analyses, Atterberg limits, natural moisture contents, specific gravity and compaction using four different compactive efforts namely reduced proctor, standard proctor, West African standard and modified proctor. The tests were carried out in line with the procedures of the British standard 1377 of 1990 and Head of 1992. The soils were found to contain kaolinite as the major minerals with some mixtures of smectite, muscovite, halloysite, quartzite, biotite and aluminium phosphate. Values of the unconfined compressive strength obtained within 12.5 and 22.5% moulding water contents equal to or greater than 200 kN/m² which is the minimum acceptable value required for containment facilities. The maximum dry density, Mg/m³ ranged between 1.68 and 1.98 while Optimum moisture content, % ranged between 12.3 and 21.2. Hence, unconfined compressive strength values were found to be greater than 200 kN/m² at dry unit weight of 16.20 kN/m³ especially when WAS and modified proctor compactive efforts were used which met the minimum required unconfined compressive strength of 200 kN/m² for hydraulic barriers in waste containment facilities.