A coal mining site at Odagbo area located in Kogi State, Nigeria, was investigated using resistivity data to detect unconsolidated zones, majorly caused by the mining of coal seam deposit. The resistivity measurement was carried out with the aid of ABEM Terrameter SAS 4000 and electrode selector equipment (ES 464). The resistivity data was acquired along three (3) profile lines at an equal interval of 50 m apart. The electrode array that was used for data acquisition was dipole-dipole array at electrode spacing of 5 m. The data acquired along the three (3) profiles were inverted with RES2DINV software. The inverted models were able to map-out air-filled/water-filled voids and showed the boundary between the unsaturated and water-saturated zone. The air-filled/water-filled voids have high (553 - 4000 Ωm) and low (3 - 70 Ωm) resistivity values with an average thickness of 11 m respectively. The unsaturated zone is 7 m thick and mostly consists of materials with resistivity values ranging from 195 to 4018 Ωm. The weathered zone is 17 m thick and is majorly dominated by water-saturated materials. The study shows that the unconsolidated zones in the subsurface of the study area lies within the weathered layer. These zones are the cause of environmental hazard and might even affect the probable potential coal resources of the study area.
The recent failure of building foundations such as cracks, structural differential settlements and collapse has now become a great concern to geoscientists. A new site at Ahmadu Bello University, Nigeria, was investigated to explore the suitability of the subsurface material for the foundations of buildings, identify weak zones that may be prone to subsidence and the competence to support massive structures. This investigation was achieved with 3D electrical resistivity tomography (ERT). The data were obtained using Terrameter SAS 4000 and ES 464 electrode selector equipment and processed using the RES3DINV software. Dipole-dipole configuration at electrode spacing of 5 m was used to acquire the data along six profiles laid in the study area. The results in correlation with borehole data showed that the subsurface has a minimum of three geo-electric sections. It can be concluded that the competent layer with high resistivity values (746 to 1206 Ωm) is recommended for building or high rising building foundations due to its fresh basement rock. In the topsoil, clay formation should be avoided, this is because the clay materials are subject to differential settlement or flow under pressure.
Vertical electrical soundings (VES) and standard penetration test (SPT) were carried out at Ahmadu Bello University Phase II, Zaria, Nigeria, with the aim of correlating between transverse resistance (T) and number of blows per counts (N-value) for foundation studies. Two (2) SPT and VES using Schlumberger electrodes array, were conducted within the study area. The VES data acquired from the field were processed and interpreted using AGI earth imager 1D software. Borehole data of exact point, where the VES was carried out were used for calibration. The results obtained from the VES depicts that the depth to basement values ranges between 6.5 and 8.0 m which agree with the borehole data obtained from the SPT results. The results of resistivities and thickness obtained from the VES curve were used to compute transverse resistance. The transverse resistance was used to correlate with the N-values obtained from SPT data. It was observed that the correlation of transverse resistance and N-value was linear and highly positive. The linear relationship that was established between the two parameters can be used to determine the soil strength at any point within the area of study.
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