Use of electrical resistivity and downhole seismic survey techniques for geotechnical characterisation of Site ‘x’ Takoradi, Ghana

The need for more detailed, robust and precise subsurface characterization for geotechnical purposes has been a burden on geotechnical engineers because of unpredictable geologic condition Hence, the demand for integrated methods of investigation, recent development in geophysical methods have improved data acquisition and interpretation. This study has further proved the effectiveness of geophysical method in subsurface characterization by employing electrical resistivity and down-hole seismic survey methods to characterize the subsurface at Aboadze, Takoradi western region of the Republic of Ghana. Electrical resistivity data were acquired using Wenner’s array method of configuration with Ohmega resistivity meterwhile the seismic data were acquired using geomotographie BGK-7 geophone and geometric geode seismograph. Resistivity results of the top layer range from 383 Ωm to 805 Ωm, typical of sandy soil with the results of the underlying layer range from 1323Ωm to 12393Ωm suggest the sandstone is highly weathered - fresh. The studyidentified a range of P-wave velocities between 1289m/s and 2674m/s and a range of S-wave velocities between 107m/s and 1351m/s. These velocity ranges were consistent with velocities expected from the study area’s geology as logged from the borehole (sands, clays, and sandstones). The correlation of SPT N values with shear wave velocity gave an empirical relationship for shear wave velocities and SPT ‘N’ values; Vs = 66.39N0.433 with a coefficient of correlation, R2 = 0.820. The subsurface geotechnical characterization methods helped in delineating soil boundaries and groundwater level, which were plagued with uncertainties.