GEOPHYSICS AS A VERITABLE TOOL IN RECONNAISSANCE STUDIES FOR DEVELOPMENT OF URBAN SETTLEMENTS

Abstract

Geophysical Methods have been applied as tools in solving many earth problems. The earth properties measured has made it a veritable tool of reconnaissance/investigation in many parts of the world including urban planning with very high need of good foundation structure and groundwater for its development and future sustenance. This investigation was carried out in Abuja which is underlain mainly by the Gneiss – Migmatite complex. The geophysical method adopted is the electrical resistivity utilizing the Vertical Electrical Sounding (VES) technique. VES was conducted at 25 stations along 5 traverses. The quantitative interpretation through partial curve matching and computer aided 1-D forward modelling with the WingLink software revealed a sequence of four major geo-electric layers which are the topsoil, weathered layer, fresh basement and fractured basement. The topsoil range in resistivity from 102 to 2400 Ωm while the weathered layer resistivity ranges from 32 – 500 Ωm. The high resistivity of the topsoil in places is an indication of its lateritization which is good for construction foundation/materials in addition to the thin overburden in the area especially in the northern portion of the area. A fractured basement trend is observed in the N-S direction beneath points B1, F, I and O in the area which is believed to be interconnected with the strip of thick weathered layer in the southern flank of the study area to a depth of about 20 m. This could be indicative of a good groundwater zone in the area considering the shallow water table observed around the study area. Information obtained from this study indicates the area can be divided into two sections with relative uniformity thereby allowing for adequate cost effective planning of geotechnical explorations.