Geophysical Investigation and Protective Capacity of Frequently Failed Road Sections of Selected Roads in Delta State, Nigeria

Abstract

Geophysical survey has been successfully carried out along failed road sections situated in Delta State, Nigeria to delineate the causes of failure along portions of the road. These were executed by using forty Vertical Electrical Sounding (VES) from Schlumberger array along road sections using SAS 1000 ABEM Terrameter. The recorded field data were processed via Winresist software. Resistivity values ranging from 22 to 1026 Wm at 15 m depth from surface were traced along Amukpe, Ekpan-Ovu, Aghalokpe, Okpara to Otumara. At Eku, Igun, Oria, Erho, and Abraka and Obiaruku, the resistivity figures procured ranged from 11 to 500 Wm at depth of 5.5 m via the topsoil, 21.5 m from sub-grade and 9.76 to 50 m along few profiles. Umutu, Urhomehe, Abavo, Urhonigbe and Agbor signal resistivity ranging from 59 to 1468 Wm for stable (lasting) and unstable (unsteady) segments of the road at 15 m depth for some profiles. Low resistivity values (≤197Wm) were observed in some trenchant regions of the profiles comprising collapsible, expansive, compressible sandy clay materials which have the capability of absorbing water. The results of the geoelectric study revealed that the failure of road portions can be attributed to the presence of incompetent clayey materials used for the filling materials and low standard materials found underneath the built road. The protective capacity echelon ranges from poor-moderate. Competent filling soil should replace the low resistivity soils from 5-7 meters below the surface when rehabilitating the road.