Characterization of terrain and biotite gneiss-derived lateritic soils of Ilorin, Nigeria, for use in landfill barriers

A total land mass of 3.63x106m2 and the biotite gneiss-derived lateritic soil over it around Ilorin, Nigeria were investigated for the purpose for locating appropriate site for the disposal of municipal solid wastes. The study shows that the investigated terrain is not only underlain by fresh Basement rock that is competent enough to provide support for the containment facility but has environmental characteristics such as safe distances from water supply wells, highways, inhabited areas, source(s) of expected waste generators and availability of soils which can be used asbarriers and final cover materials. The results of twenty-eight (28) vertical electrical soundings (VES) and five (5) handdug wells over the site revealed that the average thickness of the overburden is 17m; thickness of the lateritic layer is 7.8m on the average while the groundwater table is encountered at depth of 5.3m. The geotechnical assessment of the soil samples revealed that the specific gravity values range from 2.50 - 2.73; the percentage of fines range from 20% - 67%; liquid limits range from 21.64%-46.53% and the plasticity index values range from 13.47% - 25.95%. The maximum dry density values of the soil obtained using the standard Proctor energy of compaction range from 1.72t/m3 -1.97t/m3; while those obtained using modified Proctor energy range from 1.78t/m3 –2.07t/m3. The highest coefficient of permeability values (6.03 x 10-9m/s) for all soil samples, which is close to the recommendation of 1x10-9m/s by several previous researchers, who obtained their results by using the lowercompaction energy. All the characteristics compared favourably well with those suggested by regulatory agencies and several investigators. Consequently, this study confirms the suitability of the soils and for the construction of landfill facility