Journal of Earth Sciences and Geotechnical Engineering

Application of Geophysical and Geotechnical Methods to Site Characterization for Construction Purposes at Ikoyi, Lagos, Nigeria

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• Abstract

  An integrated geophysical and geotechnical survey was carried out in a proposed engineering site at Ikoyi, Lagos, Nigeria. The survey aimed to image shallow subsurface with a view to evaluate the stratigraphy and competency of the shallow formation as foundation materials. Geotechnical investigation involving Cone Penetration Testing (CPT) and Standard Penetration Testing (SPT) were carried out on the site. Geophysical technique involving Vertical Electrical Sounding (VES) was also implemented and the data were processed, inverted and interpreted. Geophysical and geotechnical tests showed good agreement. Four to five subsurface layers were delineated within the study area: the topsoil loose sand, peat/clay, sandy clay, sand and clay. This indicates good correlation with the soil layers in bore logs. The existence of loose sand, peat and clay near at the surface is capable of being inimical to building structures. The subsurface layers up to the depth of 16 m are mechanically unstable with low penetration resistance value which may not serve as good foundation materials. Shallow foundation is considered unsuitable for the intended building. In view of unsuitability of shallow foundation in this area, structures in this area should be safely founded in competent and mechanically stable coarse sand through pilling.