Application of Very Low Frequency Electromagnetic (VLF-EM) and 2D Electrical Resistivity Methods for Pre-Foundation Studies at Nuhu Bamalli Polytechnic, Zaria

Abstract

Information from the department of physical planning of Nuhu Bamalli Polytechnic Zaria reveal that the study area is a propose site for future development of physical infrastructure of the school and inspection of existing buildings near study area shows formations of cracks. This may compromise the building's quality, potentially leading to its collapse, which could result in the loss of lives and property. An integrated geophysical investigation involving the 2D resistivity imaging and very low frequency electromagnetic (VLF –EM) methods at propose site for future development of physical infrastructure in study area was investigated to obtained the suitability of the subsurface material for the design and foundation of buildings. The data were collected using ABEM Terrameter SAS 4000 with electrode selector along 35 profiles running orthogonally employing dipole-dipole array with an equally spacing electrode of 5m. The apparent resistivity obtained from field was processed and interpreted using RES2DINV software to produced two-dimensional image of the study area. The result of the inverted 2D resistivity imaging revealed that the site is predominantly dominated by low resistivity values at near surface with sparsely high resistivity values at some places. The low resistivity values that ranges from 37 Ωm to 139 Ωm, typifies high clay content materials which has a negative impact on any structure that will be erected on the site. The interpretation of 2D resistivity imaging shows that the 4 profiles indicated the presence of geologic structure such as fracture, fault or depression in the bed rocks. These profiles were further investigation by employing VLF-EM method in order to compliment the result obtained from the 2D resistivity model. The VLF EM data was collected along the 4 profiles selected for further investigation with an inter-station distance of 5 m along each profile and a total spread length of 200 m.