Geotechnical Investigation of Proposed Site for Building Suitability using Geological and Geophysical Methods in Ughelli Metropolis

Abstract

Vertical Electrical Sounding (VES) and Electrical Resistivity Tomography (ERT) technique have been employed to investigate a proposed building site along Ughelli-Patani Road, Ekiugbo, Ughelli North, Delta state, Nigeria. Subsurface rock(soil) type and bedrock depth with priority to aquifer depth and shallow depth profiling as an index for engineering property of the subsurface. Electrical imaging resistivity survey was carried out along three spreads with maximum spread length of 130m using the 2D-Wenner configuration in N-S dip direction, in addition to five Vertical Electrical Sounding using the Schlumberger configuration with maximum current spread (AB) of 140m. VES points were selected at strategic position with three VES points on the three ERT spreads to integrate all data. Data from 25 sample points and test borehole(14m /45ft deep) were used to support geophysical models. Geophysical models show horizontal and vertical distribution of electrical properties (resistivity values) due to the inhomogeneous subsurface. Models show layers with low resistivity values delineated as silty clay to wet clay, and layers with high resistivity values as silty sand to coarse sand. Delineated layer depth and thickness from geophysical models show high degree with sample analysis results and logs from test borehole.