In order to investigate the competence of the proposed road for pavement stability, geotechnical and geophysical investigations involving Land Magnetic, Very Low Frequency Electromagnetic (VLF-EM) and Electrical Resistivity methods were carried out along Akure-Ipinsa road Southwestern Nigeria. The magnetic profile was qualitatively and quantitatively interpreted to produce geomagnetic section that provides information on the basement topography and structural disposition beneath the proposed road. Similarly, the VLF-EM profile was equally interpreted to provide information on the possible occurrence of linear features beneath the study area. These linear features pose a potential risk to the proposed road as they are capable of undermining the stability of the pavement structure. The geoelectric parameters obtained from the quantitative interpretation of the VES data were used to generate geoelectric section. The geoelectric section generated shows that the study area was underlain by four geoelectric layers namely the topsoil, the weathered layer, the partly weathered/fractured basement and the fresh basement. The major part of the topsoil, which constitutes the subgrade, is characterized by relatively low resistivity values (<100 Xm) suggestive of weak zones that are capable of undermining the stability of the proposed road. This therefore suggests that the layer is composed of incompetent materials that are unsuitable for engineering structures. Furthermore, fractured basement was also delineated beneath some portion of the proposed road. Since fracture is a weak zone, its presence can facilitate failure of the proposed road especially when it is occurring at shallow depth. The geotechnical results reveal that most of the investigated soil samples are clayey in nature. Integration of the results demonstrates that there is a good correlation between geophysical results and the geotechnical results. Furthermore, a vulnerability section that divided the road segments into three zones based on the degree of vulnerability was produced. These zones were high, moderate and low vulnerability zones. It is estimated that about 60% of the road segments constitutes moderate degree of vulnerability while 30% and 10% of the segments respectively constitute high and low degree of vulnerability.
Geophysical and hydro-chemical investigations have been undertaken within the vicinity of Arapaja, Apete and Sabo dumpsites monolithically underlain by three different rock types namely; Migmatite Gneiss, Quartzite, and Granitic Gneiss respectively in a basement complex of Ibadan, southwestern Nigeria. This was with a view to assessing the pollution potential of the dumpsites on the soil and groundwater in the study locations. Electrical Resistivity methods involving Dipole-Dipole profiling and fifteen (15) Schlumberger Vertical Electrical Soundings (VES) were carried out across two orthogonal traverses established in each of the study locations. A maximum of three subsurface layers namely the topsoil, the weathered layer, and the fresh basement were identified from the geoelectric sections in the three locations. The weathered layer, which constitutes the major aquifer units in the areas and the overlying topsoils were suspected to have been impacted by leachates from the waste dumpsites in the three locations as revealed from characteristic relatively low resistivity values of these layers on the geoelectric sections and the 2D resistivity structures. The hydrochemical analysis of samples from wells in the three locations shows that majority of the analysed cations and anions in the three study locations were within the WHO permissible limits. However, there were indications that parameters such as Pb and Fe 2+ in Arapaja and EC, TDS. K + , NO 3 2− , Pb, and Fe 2+ in both Apete and Sabo dumpsites were higher than the acceptable limits which revealed possible contamination impacts of infiltrating leachates from these dumpsites on the ambient groundwater in the three locations. This is in agreement with the pollution index rating of these parameters which indicates that they fall within the strongly polluted and seriously polluted classes of 4 and 5. It is further concluded that Arapaja which is underlain by the Migmatite Gneiss rock shows least impact of the infiltrating leachates from the dumpsite relative to other dumpsite locations in Apete and Sabo where the underlying rock types are quartzite and granite gneiss respectively. This can be attributed to the nature of the resulting weathered profile of these rock types which is mostly characterized by impermeable clayey materials in Arapaja and by permeable sandy materials in Apete and Sabo locations.
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