Examining tunnel erosion using vertical electrical sounding and ground magnetic geophysical techniques in Awka, Nigeria

Abstract

The present study investigates the nature and characteristics of soil piping using Vertical Electrical Sounding (VES) and Magnetic geophysical techniques at Awka, Nigeria. The VES survey was conducted using a Pasi resistivity meter, while the ground magnetic survey was carried out using a proton precision magnetometer. The VES survey revealed two to five distinct geo-electrical sections and fourteen characteristically sounding curves, which indicate vertical changes in the subsurface. The findings illustrate that the weathered soil in proximity to the surface of the study area has the best soil formations that encourage soil pipe development. Moreover, the iso-resistivity 2D maps demonstrate that the soil pipes describe a direction in the NW-SE, which is consistent with the stress direction, fluid migration paths, and sloppy terrains of the study area. The results of the ground magnetic survey were obtained using a diurnal corrected anomaly technique generated from the field. This finding suggests that low magnetic susceptibility, ranging from -124.4 to -300nT, has accumulated in the subsurface, primarily in the south-western region, where most of the soil pipes are located in the surveyed areas.