Geophysical investigation using 2-D imaging was conducted along Ganaja road, Lokoja to ascertain how resistivity technique can be used to delineate resistivity variations within the subsurface and determine which zone(s) may pose a danger to the highway. Wenner array was used to obtain a profile at each location on the highway with the aid of ABEM Terrameter SAS 4000 taking the measurements. The acquired field data were processed and inverted using a 2D modelling inversion algorithm (Res2DINV@ software) and surfer@18 software. Resistivity values with their respective depths were delineated across the entire profiles in the study area: Profile A, Profile B, Profile P and Profile R (456 Ωm – 5.02Ωm, depth 2.65 -3.98m, 21.80 Ωm – 53.2 Ωm, depth of 03.98 m, 4.65 Ωm – 15.83 Ωm to a depth of 3.98 m and 3.50 Ωm – 61.80 Ωm, depth of 3.98m) respectively. Results revealed the presence of low resistivity values materials suggestive of clay at several portions of profiles A, B, P and R. Increased sandy clay contents account for the low resistivity values causing differential settlement suspected to be responsible for the failure. It is suggested that portions containing the sandy clay should be excavated to a depth of 4–6 meters and rebuilt with competent materials.
Key words: geophysical investigation, road failure, sandyclay, competent materials
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