Geophysical Investigation of Road Failure: A Case Study of a Typical Domestic Road in South Western Nigeria
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Faculty of Science, University of Lagos.
An integrated geophysical survey involving Very Low Frequency Electromagnetic (VLF-EM), dipole-dipole profiling and Vertical Electrical Sounding (VES) resistivity methods were carried out along the Federal Housing Estate road in Ondo Town, Ondo State Nigeria. The purpose of the study is to examine the subsurface structures responsible for road failure in the area. The study area lies within latitudes N7º 7ˈ 29.48ˈˈ to N7º 7ˈ 36.55ˈˈ and longitudes E4º 52ˈ 33.91ˈˈto E4º 52ˈ 56.75ˈˈ. Twenty-eight VES stations were occupied at an interval of 20m on the stable and unstable portions of the road with current electrode AB/2 of 65m. Three VLF-EM traverses were laid at 5m intervals while the dipole-dipole profiling was carried out with electrode separation of 5m. The VLF-EM, dipole-dipole and VES data were processed and analyzed using KarousHjelt, Dippro and Win Resist software, respectively. The VLF-EM results showed positive peak amplitude at various distances in the three traverses surveyed. Likewise, the dipole-dipole 2D resistivity model result delineated low resistivity clay at distances 100-140m, 150-180m, 300m, 315m, 380m and 420- 435m and the VES geo-electric sections revealed six geo-electric layers: topsoil, clay, weathered layer/weathered basement, fractured basement, basement and fresh basement with varying layer resistivities and thicknesses. Results revealed that the presence of clay beneath some sections of the road was the major cause of failure along the road. In addition, the clayey nature of the topsoil and the sub-grade also contributed to the failure of the unstable sections of the road
Ondo town, Vertical Electrical Sounding, Dipole-Dipole, Road failure