Application of 2-D imaging survey for ascertaining the cause(s) of road failures along Sapele/Agbor road in Delta State, Nigeria
Surveying involving 2-D imaging dipole–dipole geophysical technique was carried out along Sapele-Agbor Highway situated in Southern, Nigeria to determine the primary causes for Highway pavement failure. Twelve profiles spreading over 100 meters were in each cases conducted on road surface sections along the stable (control) and unstable portions of the road. Data were gathered together along the various profile employing ABEM Terra meter SAS 1000. The field data were processed and inverted utilizing Dipro software. This was done by specifying and locating the geoelectric arrangement within the surface, sub-base and sub grade soil to obtain the confirming cause(s) of the road associated with pavement failure. Geoelectric sections identified four geologic layers embracing the topsoil, clayey, laterite and sand. The sections failure is due to disparity of the material used for road model (construction) as some comprises of clay materials. The results show the presence of low resistivity values at several subdivisions of the 12 profiles. Resistivity values varying from 21.60 Ωm – 1026.0 Ωm to a depth of 14.92 m from the surface was observed along Okpara Water side, Aghalokpe and Otumara. In Igun, Eku and Obiaruku resistivity values ranges from 10.5 Ωm – 500.0 Ωm to a depth of 5.5 m from the topsoil, 22 m from sub grade and 9.8 m - 50 m were observed along the four profiles. Urhomehe, Urhonigbe, Abavo and Agbor indicate resistivity ranging from 59.25 Ωm – 1467.50 Ωm for stable and unstable sections of the road with depth up to 15.0 m for some profiles. Low resistivity values, not greater than 199 Ωm observed in some distinctive regions of 12 profiles comprises of expansive, compressible, collapsible and sandy clay materials which have the capacity of absorbing water. These make the roads swell and collapse leading to road failure under stress and strain. Many stable portions of the road are characterized with high resistivity value greater than 199 Ωm, mostly laterite materials. Competent fill soil should replace low resistivity soil to a depth of 5 m – 7m from the surface of the road. Good drainage system is also recommended within the unstable road sections.