Journal of Earth Sciences and Geotechnical Engineering

Subsurface Structural Characterization of Filatan Area A, Zaria – Kano Road, using the 2D Electrical Resistivity Tomography

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• Abstract

  The method adopted for this paper was the 2D Electrical Resistivity Tomography (ERT), using the ABEM LUND Imaging System. A Wenner configuration WEN32SX was carried out to map the electrical properties as an aid to characterizing the subsurface conditions around Filatan area, Zaria aimed at determining the depth to the competent stratum in the subsurface and delineation of areas that are prone to subsidence or some form of instability, study the groundwater potential with a view of determining the depth to the bedrock and thickness of the overburden and probable depth of sewage system. Four profiles were occupied in the study area. For each profile, the layout geometry for the electrical imaging was such that two reels of cables were used with 5m intervals between the takeout electrodes. However, the two innermost electrodes adjoining the two reels of cables were connected together thus yielding a total of 41 electrodes and a spread length of 200m. The data obtained using ABEM Terrameter SAS 4000 were processed using RES2DIVN software. Based on the electrical images obtained in the study area, the following deductions were made. The depth to the fresh basement is generally well beyond 30.0m. The study reveals the presence of three to four distinct layers respectively; the topsoil, weathered basement/partly weathered basement and fresh basement with resistivity values ranging from 28 - 95Ωm for topsoil, 95 - 276Ωm for weathered basement, 97 - 815Ωm for partly weathered basement and as high as 2435Ωm for the bedrock (fresh basement). These layers constitute the overburden with a thickness of 29.3m revealed by the pseudosections. The topsoil composed of laterite and brownish sandy clay with an average thickness of 11.0m, which are indications of soil conditions requiring serious consideration in the design of massive engineering structures because of their low load-bearing capacity. The weathered basement underlies the topsoil with an average thickness of 18.3.0m and this is a good aquifer in the study area. The depth of sewage system in this area should not exceed 10m to avoid groundwater contamination since the entire area is shallow to the aquifferrous zone.