GEOPHYSICAL INVESTIGATION USING ELECTRICAL RESISTIVITY METHOD TO DETERMINE THE CAUSES OF FAILURE OF SOME SEGMENTS OF LAPAI-PAIKOROAD, NIGER STATE, NIGERIA

Abstract

Geophysical investigation involving electrical resistivity technique was carried out at Lapai Local Government Area, Niger Stat, North-Central Nigeria  with a view to determining road's subsurface geo-electrical characteristics, defining the areas of the road pavement that have failed and those that have remained stable and proposing solutions for reducing the number of road failures in the study area.Nine (9) vertical electrical soundings (VES) were conducted at three different places using resistivity meter (SAS 1000) and its accessories. The study delineated points in the study area with underlying materials and depth to bedrock by using geophysical investigation. The field data obtained was analyzed using WinResist software and contour maps were generated using Surfer 11 software. The study has revealed geo-electric layers for failed segments of Cheche VES 1, 2, and 3 and University gate VES 2 that include topsoil, highly weathered basement (clayey formation), and fresh basement, while geo-electric layers for stable segments are shown in Gada-Biyu VES 1, 2, and 3 and University gate VES 1 and 3 that include basement, weathered basement (Crystalline rock  formation), and new basement. Presence of high moisture clay in the subsurface accounts for the low resistivity of the failed segments. Because of its high porosity and low permeability, the clayey formation is not suitable for use as a sub-grade because it absorbs water and swells, resulting in high conductivity or low resistivity, as well as differential layer settlement.