Williams T.Ifarajimi - Department of Geosciences, University of Lagos. Akoka, Nigeria
Michael I.Oladapo - Department of Applied Geophysic s, Federal University of Technology, Akure, Nigeria
Sunday Bayode - Department of Applied Geophysics, Federal University of Technology, Akre, Ondo State, Nigeria

Electrical resistivity tomography (ERT) has been applied with geotechnical techniques such as Cone Penetrometer Test (CPT) and laboratory tests for subsoil characterization to investigate the causes of the deteriorated highway pavement. Eleven Electrical Resistivity (ERT) Profiling lines were established using Wenner array configuration in combination with ten cone penetrating data and eleven soil samples. The inverted ERT data consist of two to three geoelectric layers and were interpreted as topsoil (clay/sandy clay/clayey sand/sand), sand/saturated sand and dry sand/highly resistive sand/weathered rock with overlying resistivity values ranges between ۲۳ – ۵۵۰ Ω m, ۱۰۰ – ۱۰۰۰ Ω m and ۵۰۰– ۲۸۰۰ Ω m respectively. The cone penetrometer test (CPT) value ranges from ۳۰ to ۸۲ kg/cm۲. In addition, the laboratory analyses conducted on the bulk soil samples taken at ۰ - ۱ m depth includes; the optimum moisture content (OMC), maximum dry density (MDD), and California Bearing Ratio (CBR) ranges from ۱۱.۳ to ۱۲.۲%, ۱۷۲۰ kg/m۳ to ۱۹۶۰ kg/m۳ and ۸ to ۱۳% respectively, while for the Liquid Limit and Plasticity Index tests of the soil samples gives ۲۸ to ۵۲% and ۹ to ۱۷% respectively indicating that the subsoil material within study area are of poor to good geotechnical properties. The results of the integrated approach, including both geophysical and geotechnical methods have helped to identify the cause of the highway deterioration in some part of the study area which is attributed to the poor subgrade material along the region. Thus, the need for soil improvement can be implemented to enhance the stability of the subgrade materials in the poor region for subsequent road construction and design.

Electrical Resistivity Tomography, Cone Penetrometer Test, subsurface characterization, road construction