GEOPHYSICAL AND GEOTECHNICAL ASSESSMENT OF THE SUBSOIL ALONG IKORODU – SHAGAMU ROAD, SOUTHWESTERN, NIGERIA

Authors

  • Adeniji Tajudeen Akinpelu Department of Physics, Olabisi Onabanjo University, Ago – Iwoye, Ogun State, Nigeria
  • Joseph Olakunle Coker Department of Physics, Olabisi Onabanjo University, Ago – Iwoye, Ogun State, Nigeria
  • Oluwakayode John Aremu Department of Physics, Olabisi Onabanjo University, Ago – Iwoye, Ogun State, Nigeria
  • Eguono Onoriode Disi Department of Physics, Olabisi Onabanjo University, Ago – Iwoye, Ogun State, Nigeria
  • Olalekan Rasaki Liadi Department of Physics, Olabisi Onabanjo University, Ago – Iwoye, Ogun State, Nigeria

Abstract

Electrical resistivity imaging (ERI) and Vertical electrical sounding (VES) surveys were carried out
on a portion of Ikorodu - Shagamu road, Lagos State Polytechnic area in order to investigate the
subsurface geological structures, depth to bedrock and thickness of weathered basement of the area.
ABEM Automatic LUND Imaging System (Terrameter SAS 1000 and ES 464) employing the
Wenner array, was used for the investigation of 2-D resistivity data sets along two profiles and seven
VES conducted on the profiles. The acquired data were processed and interpreted using RES2DINV
software to produce the 2-D image of the study areawhileIPI2Win software was firstly applied to
perform an automatic approximation of the initial resistivity and thickness of the various geo electric
layers and later filtered with Win Resist iteration. The geochemical method employed California
Bearing Ratio (CBR) test conducted on four samples at a depth of 0.6m to determine the load bearing
capacity of the soil samples. The results of the geophysical methods showed three to five geo electric
layers described as topsoil, clay, sandy clay, clayey sand and dry sand based on corresponding
resistivity values while the results of the California Bearing Ratio (CBR) of the soil samples ranged
between 16% and 21%.Thus, the higher the CBR value of a road's subgrade, the lower the thickness of
the required road pavement. The correlation of the integrated geophysical and geotechnical results
implied that, at the weathered layer we have clay/sandy clay with a depth 1.2m – 17.2m interpreted as
fairly competent and moderately stable while at the last layer, are clayey sand and dry sand with depth
2.1m – 31.0m interpreted as competent and stable soil. The subsoil assessed is suitable as subgrade,
especially after the removal of the topsoil/weathered layer. The unsuitable portion along the length of
the road can be excavated and replaced with a competent stable soil as subgrade

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Published

2022-09-14

Issue

Vol. 11 (2020): SPECIAL EDITION 1

Section

Articles