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Abstract

A shallow electromagnetic evaluation of Federal University of Technology, Akure, Nigeria main road base integrity has been undertaken in this study with the aim of identifying probable zones of untimely failure. Controlled-Source Electromagnetic Method (CSEM) was adopted for the study. The road segment investigated is underlain by four different lithologic units, which are the migmatite gneiss, quartzites, charnockite and granites along the west-east direction of the campus. Quadrature phase (conductivity) and in-phase (magnetic susceptibility) were measured in both vertical and horizontal dipoles. While the vertical dipole mode has a probing depth of 6 m, the horizontal dipole mode probes at a depth of 3 m. The range of quadrature and in-phase values obtained for horizontal dipole mode is from 6 to 50 mS m-1 and 0.808 to 20.47 ppt, respectively. For vertical dipole mode, the range of quadrature and in-phase values are -21.00 -71.00 mS m-1 and -20.07 to 20.47 ppt. The ratio of vertical conductivity value (CV) to horizontal conductivity value (CH) i.e., CV/CH was utilized in assessing road-base performance. Road stability was observed where this ratio is greater than 1 (CV/CH>1) while signs of distress characterized where the ratio is less than or equal to 1 (CV/CH = 1) in vertical dipole. Likewise, relatively high magnetic susceptibility values in vertical dipole mode characterized zones of early distress. This technique is presumed useful in fast and cheap roadwork performance evaluation.