Pages: (1-23 )
Abstract
Recurrence of structural failures universally has demanded application of geophysical methods to survey the
subsurface geology at a construction site for civil engineering structures. Combined ground magnetic and electrical
resistivity methods in form of electrical Depth Sounding Survey (DSS) and electrical resistivity profiling (dipole-
dipole array) were conducted at Akinola area, Ile-Ife, Southwestern Nigeria. The study aimed at providing
comprehensive information of subsoil profiles for durable and sustainable civil engineering structures. The magnetic
profiles were interpreted qualitatively and quantitatively to generate 2D models that supply information on the
structural features (faults/fractures, dykes, or water-bearing fracture zones) and basement reliefs underneath the study
area. Likewise, dipole-dipole data obtained from the electrical resistivity profiling were processed and interpreted to
produce 2D resistivity structures that revealed the likely existence of linear features underneath the study area. DSS
data were qualitatively and quantitatively interpreted to generate geoelectric parameters that were used to produce
geoelectric sections. The geoelectric sections reveal four geoelectric layers: the topsoil (clayey, sandy, lateritic),
weathered layer (clayey, sandy, lateritic), fractured basement, and fresh basement underlying the study area. The
geoelectric sections, 2D resistivity structures, and 2D magnetic models showed good comparison and revealed the
presence of subsurface geological structures such as fault/fracture or water-bearing fractured zones. These zones are
capable of deteriorating the bearing capacity of the subsoil/parent rock and could cause differential settlement in the
foundation of engineering constructions particularly at shallow and intermediate depth. The study therefore,
recommends excavation and refilling of low competent (clayey) layers with competent materials and reinforcement
of the weak zones.
Keywords: Subsurface appraisal, Depth sounding survey, Electrical resistivity, Water-bearing zones,