Geophysical Investigation of Bulding Distress in Gashua, Nigeria

Abstract

Gashua is the Headquarter of Bade local government in Yobe State, it has a population of about 125, 000 according to the 2006 population census. It is a densely populated town located in a flood plain within the Chad Basin. In an attempt to proffer solutions to the prevailing building distress in Gashua and its environs, this study was carried out to accurately characterize the subsurface geology of the area, thereby reducing the incidence of building failure in the area to minimum. In this study, electrical resistivity method was used to determine the causes of building distress and failure in Gashua and its environs. Vertical Electrical Sounding (VES) using Schlumberger array and Electrical Resistivity Tomography (ERT) were adopted for the study. The results of the VES survey showed that the area is composed of five geologic layers which are; the topsoil, clay, sand, sandy-clay, and sand. The ERT results showed that most of the building foundations in the study area were laid within the second layer which is a clay formation. The findings of this study showed that the building distress and failure which are common in the study area were caused by the volumetric changes of the clay formation due to hydrological dynamics. The clay formation absorbs water during the raining season and swells up, and during the dry season it shrinks, this changes in the volume of the clay formation underlying the building foundation in the study area induces a significant mechanical stress on the buildings leading to the formation of cracks, voids, fissures and fracturing of the buildings, which eventually culminate into collapse. In this study, electrical resistivity method of geophysical investigation has demonstrated to be a veritable tool for geotechnical soil evaluation. Based on the findings of this study, geophysical investigation of a proposed site...