Engineering Geological Evaluation Of A Proposed Landfill Site At Aba-Kulodi, Near Ibadan, Southwestern Nigeria

Evaluation of a location at Aba-Kulodi adjacent to kilometre 8 along the Ibadan / Ile-Ife expressway, Southwestern Nigeria was carried out to determine its suitability or otherwise as a landfill site. Two Vertical Electrical Soundings (VES) 30.00m apart were executed to obtain subsurface information on depth to bedrock and possibly the water table. Disturbed and undisturbed soil samples were collected from each of the two trial pits established at vertical interval of 0.50m up to a depth of 3.00m. The disturbed samples were subjected to grain size distribution and consistency limits tests while consolidation and permeability tests were carried out on undisturbed samples. The VES results revealed 3 geo-electric layers with depths to bedrock of between 14.30m and 17.60m at VES 1 and VES 2 respectively. The depths to water table measured from an existing nearby well were 8.10m and 7.00m during the dry and rainy seasons respectively, suggesting that the water table lies within the second geo-electric layer. The soil samples taken from the depth of 3.00m in the two pits are generally well-graded non-plastic sandy clayey silt, a possible indication of no compressibility. The coefficients of permeability obtained for samples from pits 1 and 2 ranges from 1.85 x 10–4mm/s to 3.91 x 10-6mm/s and 1.91 x 10-4mm/s to 2.91 x10-6mm/s respectively. The coefficient of permeability obtained for samples taken from the 3.00m depth in the two pits are significantly higher than the minimum value of 10-6mm/s recommended for soil that should form the base of landfills. The coefficient of volume compressibility at the sampling pits 1 and 2 range from 1.83 to 7.69 x10-3 m2/KN but generally increases with applied pressure (31.2 - 498.9 KN/m2) and decrease with depth (0.5 to 3.0m). Statistical treatment of the values of the coefficient of compressibility of soil samples from the depth of 3.00m in the two test pits shows no significant variation, an indication that there is no likelihood of differential settlement if the site is used for disposal of solid wastes. If in-situ compaction and lining are done, the location can be used as a landfill site. KEY WORDS: Landfill, Plasticity, Compressibility, Permeability, Compaction. Global Journal of Geological Sciences Vol.3(1) 2005: 25-3