Effectiveness of 2D Induced Polarisation & Electrical Resistivity Tomography in Mapping Fracture Heterogeneity in Foundation Soils.

Abstract

Inhomogeneity caused by fractures can constitute real problems in foundation soils which consequently can lead to structural failure. 2D Electrical Resistivity Tomography (ERT) has been exceedingly popular in mapping near surface discontinuities that can possibly affect engineering structures. The effectiveness of using Induced Polarisation Tomography (IPT) in mapping subsurface fractures was explored. Using the same field way out for both ERT and IPT, investigations were carried out at a failed structure with foundational inhomogeneity in the Nsukka area, Southeastern Nigeria. Four Electrical Resistivity Tomography (ERT) and four Induced Polarisation Tomography (IPT) were carried out. Electrical Resistivity Tomography for profile line one (ERT1) and that of the opposite section, ERT3, revealed a fault trending NNW- SSE. This anomaly was also observed on the Induced Polarization Tomography for profile line one (IPT1) as well as that of profile line three (IPT3) at the same offset distances, delineating the same fracture zone. A second fault trending in NE-SW was mapped by the Electrical Resistivity Tomography for profile line two (ERT2) and Electrical Resistivity Tomography for profile line four (ERT4). The fault was also visible in the Induced Polarization counterparts, IPT2 and IPT4. Field validation along mapped trends recorded subtle cracks on the foundation along the same trend detected by the IPT as well as the ERT.