ActaSATECH Journal of Life and Physical Sciences: ISSN: 15971007

Subsurface Appraisal for Foundation Study using combined Geophysical Techniques: A Case Study of Akinola-Ipetumodu in Basement Complex Southwestern, Nigeria

Authors: Adenika Charles I, Arogundade Augustine B, Alao Olatunbosun A,

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,

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