EXPLORING THE LINKAGES BETWEEN GEOPHYSICAL AND GEOTECHNICAL PROSPECTION TO DETECT FOUNDATION FAILURE OF BUILDINGS IN A WETLAND AREA OF LAGOS, SOUTHWESTERN NIGERIA
Authors: *Adeoti L, Opene-Odili P.N, Oyedele K.F, Oyeniran T.A, Ishola K.S, Ayuk M.A
The geophysical and geotechnical methods were used to characterize the sub surface geologic units with a view to establishing the causes of foundation failure at Oyadiran Estate, Yaba, Lagos, Southwestern Nigeria. 2–D Electrical Resistivity Imaging, Vertical Electrical Sounding (VES) and Multichannel Analysis of Surface Wave (MASW) were acquired within the study area. Also, a Standard Penetration Testing (SPT) boring was acquired to constrain the geophysical methods. The results of 2–D resistivity and 1-D geoelectric sections delineated four to five geologic units. These correspond to topsoil, clay/peat, sandy clay, clayey sand and sand based on resistivity contrast ranging from 0.25 – 226 ?m. The 2–D resistivity sections emphasized the lateral and vertical extents of the subsurface geological information. The MASW results revealed similar geologic units based on shear wave velocity discrimination except in a few cases which might be due to subsurface dip of the earth materials. An analysis of a typical geotechnical borehole has assisted to classify sand into loose, medium dense and dense based on SPT N-values and clay into very soft arising from cohesion (cu) value. This study has established that the clay materials with resistivity in the interval of 0.25 – 27 ?m, Vs values 60 – 80 m/s2 and Cu of 12 -15 kN/ m2 could be responsible for the foundation failure. Hence, the integration of 2–D Electrical Resistivity Imaging, VES and MASW complemented with a SPT boring has assisted to reduce this uncertainty by identifying the anomalous zones for detailed and cost effective geotechnical investigation.
Affiliations: Department of Geosciences, Faculty of Science, University of Lagos, Akoka, 100213, Nigeria
Keywords: Vertical Electrical Sounding, Shear Wave Velocity, Standard Penetration Testing, Anomalous Zones, Foundation Failure
Published date: 2018/06/30