Integrated Geophysical Investigation of the Failed Portion of Minna-Zungeru Road, Minna Niger State

Abstract

Very Low Frequency Electromagnetic (VLF EM) and Vertical Electrical Sounding (VES) geophysical methods were used to investigate the competency of kilometer 37 Minna – Zungeru road, Latitude 9038'37'' N to Latitude 9039'06'' N, Longitude 6016'09'' E to Longitude 6015'20'' E and altitude 682 feet to 597 feet. The study is aimed at investigating the causes of road failure other than the constructional factors that were generally believed. Two VLF – EM traverses which are 1.22 km long were established by the sides of the road segment, which cut across the unstable, fairly stable and stable portions. In these traverses, readings were taken at 20 m interval with SCINTEX ENVI VLF. The data were further filtered, analyzed and plotted with Karous Hject filtering. The inphase and quadrature were plotted against the distance which reveals the conductive zones (positive peak of the raw real). 16 VES were acquired with ABEM SAS 1000 tarrameter along the two traverses. These VES were sounded at the positive peak of the raw real VLF plot using Schlumberger array electrode spacing of 100 m. Geological sections were produced from the iterated VES curves produced with Winresist. The geoelectric sections revealed three geological layers which are the top soil, weathered layer and the fresh basement. The resistivity and depth of these layers ranges from 14 to 98, 81 to 990 and 1184 to 12, 940 Ωm 0.5 to 3.2, 1.6 to 39.4 and 3.5 m to respectively. The geological factors responsible for the road failure susceptibility are based on clayey subgrade beneath the road pavement, water fluctuation in the saturated zone and lateral inhomogeneity.