Integrated Geosciences Subsurface Exploration for Engineering Construction in a Basement Terrain

Non-invasive 2-Dimensional Electrical Resistivity Tomography (ERT) and 1-Dimensional Vertical Electrical Sounding (VES) were integrated with invasive geotechnical soil analysis to characteristics the subsurface of a proposed engineering construction site in a Crystalline Basement complex area. The geophysical results indicate the subsurface to be characterized by three major geoelectric layers. The 2D ERT established weak subsurface areas that were further probed with invasive geotechnical investigations. The geotechnical investigation involved the performance of five (5) Dynamic Cone Penetration Tests (DCPT), and establishment of three (3) Trial Pits. The strength tests, indicate an allowable bearing capacity range of 199 kN/m ² to 217 kN/m ² obtained at 2.0m to 3.0m depth ranges. The magnitude of consolidation settlement is within 25mm maximum as specified for building structures. Based on the bearing capacity and the shallow water table observed over the site, a Pad foundation sited at depth of 1.5m is recommended for the proposed structures on site. The Foundation should be designed with bearing capacity not greater than 180 kN/m2. This study shows that the integration of geoscientific methods for subsurface study regarding engineering structures cannot be overemphasized.