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Integrated geophysical and geotechnical assessment of the permanent site of Adekunle Ajasin University, Akungba Akoko, Southwestern, Nigeria

Oluwafemi O. and Ogunribido T. H. Tolulope

An integrated geophysical and geotechnical investigations were carried out at the permanent site of Adekunle Ajasin University, Akungba Akoko, southwestern Nigeria to determine the suitability of the soil as foundation support for engineering structures. The geophysical methods used for the investigation were the Very Low Frequency Electromagnetic (VLF - EM) and the Electrical Resistivity methods (ER). The VLF-EM measurements were taken at an interval of 20m along six traverse lines. Sixteen vertical electrical sounding (VES) were carried out. Four major geoelectric layers were delineated: the topsoil, weathered layer, fractured layer and fresh basement with resistivity ranging from 70 - 708 Ωm, 26 - 300 Ωm, 124 - 783 Ωm and 1383 – 40272 Ωm respectively. The thickness varies from 1.7 - 4.0 m, 0.6 -10.5 m and 3.0 – 27.0 m. The depth to the bedrock was less than 36.0m. Five soil samples were collected at depth of 1metre and were subjected to geotechnical tests such as compaction, consistency limits, unconfined compressive strength, specific gravity and California Bearing Ratio. Geotechnical properties indicates that the soil is good for engineering construction or as fill materials and geophysical investigation shows that the foundations of sky -scraper should be erected on piles to carry the loads to competent soil. Adequate measures should be taken since part of the study area is consisting of clay and clayey sands at shallow depths to avoid foundation failure or sudden collapse of engineering structures. Geotechnical problems could also be avoided, by the construction of drainage channels for run-off.