Evaluation of near-surface conditions for engineering site characterization using geophysical and geotechnical methods in Lagos, Southwestern Nigeria

Abstract

ABSTRACT The geological condition of the site in Lagos was investigated using integrated methods. This was necessary following evidence of structural defects prevalent in the area. Against this backdrop, measurements were carried out using in-situ geotechnical and geophysical techniques. The techniques were the Standard Penetration Test, Cone Penetration Test, Electrical Resistivity and seismic refraction surface waves. The various data were collected along eight (8) traverses established strategically in the study area in order to obtain the most desirable results. The results obtained generally show that a low resistive and highly compressive soft soils of organic peats/clays are prevalent in the study area. These geomaterials are characterised with low SPT-N values, low penetrative resistance, low bearing capacities and low electrical resistivity values. The shear (weak) zones have also been identified particularly in the inverted resistivity models. These geomaterials are unfriendly, inimical and severe enough to cause instability in ground conditions. The peat/clay and the weak zones could possibly be responsible for the various degrees of structural defects observed in the study area and should be avoided as foundation placements.