A combination of electrical resistivity and cone penetration test techniques for subsurface assessment

Abstract

Geophysical and geotechnical methods were used with the aim of characterizing the subsurface in order to identify the cause of differential settlement of the structures in the Adeniji Adele Low Cost Housing Estate, Lagos Island, Lagos State. Twelve (12) Schlumberger Vertical Electrical Soundings (VES), five Wenner 2D resistivity imaging and eight Cone Penetration Test (CPT) data were acquired. The acquired VES, 2D data and CPT were processed .The integration of the VES and 2D resistivity imaging results reveal three to four geoelectric layers which are representatives of uneven distribution of subsurface soil materials corresponding to topsoil, sandy clay, clay and sand. The analysis of CPT data also delineates similar lithology but terminated at shallower depth. The conductive unconsolidated clayey soil / peat with the resistivity values 0.9 – 10 Ωm cum CPT values 2 to 4 kg/cm² experienced along noticeable depressed parts could have contributed to the cracking and differential settlement of the residential buildings in the study area. However, boring via percussion drilling should be embarked upon within the study area to confirm these findings.

Keywords: Geophysical, Geotechnical, Unconsolidated, Competence, Settlement, Cracking