Geophysical and petrographic evaluation of the earth’s subsurface is of vital concern, especially prior to geotechnical and hydrogeology works. Vertical Electrical Sounding (VES) of Ire-Akari Estate of Apatapiti Community in Akure South was carried out to assess the effects of the petrographic properties of charnockitic rocks on the geotechnical and hydrogeologic systems. The three curve types identified within the study area are AA, KH and HA, with a predominance of KH curve type, which suggests that the predominant geologic sequence comprising the topsoil has a clayey content alternating with laterite. This is underlain by weathered layer and fresh bedrock. Petrographic analyses revealed the presence of plagioclase (Albite-Anorthite), hypersthene, biotite, quartz, hornblende, microcline, pyroxene and dark-coloured minerals, with an average modal composition of 31%, 15%, 11%, 18%, 13%, 1%, 5% and 6%, respectively. A correlation of both results showed that the topsoil is mostly of about 0.4 m to 2 m thick layer of clay, indicative of weathering of feldspars. This is underlain by 0.8 m to 7 m thick layer of lateritic clay which responds as a low resistive layer. However, the mineral composition at location 1 is characterized by rocks that are more resistant to weathering due to the presence of low plagioclase in the rock sample compared to samples from other locations with a higher percentage of plagioclase and hypersthene minerals. This implies that weathering condition at all locations except location 1 could be favorable to hydrogeology if there are interconnected fractures in the parent rock (charnockite). However, since the area is predominantly covered by clayey materials which are established as poor foundational materials, appropriate ground improvement techniques and in-depth geotechnical analyses should be performed to forestall hazards associated with them.
