Use of electrical resistivity and cone penetrometer test techniques for foundation designs

Abstract

Characterization of subsurface conditions is a prerequisite for the estimation of soil’s physical properties for the foundation designs of engineering structure. This is necessary to provide adequate knowledge of different soil strata in ensuring good supports for structures. To this end, the electrical resistivity method (ERM) and Cone Penetrometer Test (CPT) were carried out in the study area. Ten Vertical Electrical Soundings (VES); five 2D Electrical Resistivity Imaging (ERI) measurements and two CPT data were acquired. For the VES measurements, the geoelectric sections revealed four to six layers corresponding to the topsoil, sandy clay, clayey sand and sand. In the 2D ERI measurements, five inverted resistivity sections (IRS) produced revealed three distinctive zones which are low, intermediate and high resistivity with the substrata made up of clay, sandy clay/clayey sand and sand layers. The results of the 2D ERI agree reasonably with the VES inverted results. The CPT sounding curves show that loose sand with a low load resistance of 25 – 40 kgf/cm² was encountered at a depth of about 1 m. The second layer with load resistance between 40 – 125 kgf/cm² and thickness of 1.5 m suggested a medium dense sand. However, a load resistance of 120 - 130 kgf/cm², encountered beyond 2.5 m indicated sand layer within this region, though the thickness could not be determined. It follows from these results that deep foundation design could be constructed in the sandy region which is not less than 15 m to the competent layer in the study area.