Application of electromagnetic and electrical resistivity methods for foundation studies at Ahmadu Bello University Phase II, Zaria

Abstract

Very Low-Frequency Electromagnetic (VLF-EM) and 2D electrical resistivity survey were carried out at the Ahmadu Bello University Phase II in order to investigate the suitability of the soil materials for the foundation of super-structures in the study area. The Terra-Plus equipment and ABEM SAS 4000 were used for VLF-EM and resistivity data acquisition respectively. The VLF-EM Data were collected along five (5) profiles at station interval of 10 m along each profile. The data collected from each of the VLF-EM profile were processed and interpreted with the aid of Karous-Hjelt and Fraser filter software. Electrical resistivity profile was laid on the weak zones revealed by the 2D VLF-EM profiles through the aid of dipole-dipole configuration. The data obtained were processed and interpreted with the aid of Res2Dinv software. Borehole log of the study area was used as additional information which serves as a calibration tool. The 2D imaging profile of VLF-EM highly correlates with resistivity profile. The 2D VLF-EM and resistivity profiles revealed the conductive zone and resistive zones. These zones are suspected to be geological features (dyke, faults and fractures). This geological feature such as fracture zones was filled with an earth’s materials which are probably sandy clay and mottled clay, and these materials are highly undesirable for the foundation of building structures due to its characteristics of swelling and contracting during rainy and dry season respectively. Thus, undesirable materials should be excavated and be refilled with suitable materials for the foundation of super-structures and also, geological bodies should be avoided when the foundation of the structures is to be erected.

Keyword: VLF-EM, electrical resistivity, foundation of super-structures, geological feature, undesirable materials