Investigation of causes of structural distress in Iwaya area, Lagos, southwestern Nigeria

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Oloruntola, M.O.
Bayewu, O.O.
Rafiu, S.O.
Ojekunle, V.O.
Mosuro, G.O.
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Center for Applied Science and Technology Research/Faculty of Apllied Science and Technology, IBB University , Lapai, Niger state
The prevalent of failure of small structures (bungalow) in Iwaya area, Lagos, southwestern, Nigeria was investigated with a view to evaluating factor(s) responsible for many defective buildings in the area. Ten Vertical Electrical Soundings(VES) and five Cone Penetrometer Tests(CPT) were carried out on five traverses. One borehole was drilled close to a distress structure. Disturbed and undisturbed samples recovered from the borehole were used for grain size analysis, oedometer test and quick undrained triaxial test at depths(m) of 12.75,16.50 and 33.75m. Standard Penetration Tests (SPT) were carried out in cohesionless soil at depth of 34.00, 36.00 and 39.00 m. The VES revealed three to four Geoelectric layers composed essentially of topsoil (17.8-37.3 ohmmeter) made up of fill materials, relatively thick soft clay/ peat(2-12ohm meter) of 13.8-25.3m thickness, overlying clay/sandy clay layer (28-115 ohmmeter). The CPTs showed an area with markedly varying bearing capacities at depth of 0-15.25m. Cone resistance varies from 8-128kg/cm2, having very low cone resistance (2-5.4kg/cm2)up to depth of 13m in some areas. Computed allowed bearing capacity (qa) varies from 5.4-394.2KN/m2 while in areas with distressed small structures, the qa is mostly 5.4KN/m2 up to a depth of 10-12m confirming presence of soil too weak to support small loads. The SPT revealed the occurrence of medium dense sandy unit having N-value of 12-28, at depth of 34.0-40.0m. The values of cohesion at 65.5, 12.75 and 33.75m are 65KN/m2,50KN/m2 and 72KN/m2,with corresponding angles of internal friction of 10°, 7° and 12° respectively Computed settlement of compressible clay layer gave 212mm for a load of 15KN/m2 imposed on the peaty/soft clay. Preponderance of distressed small structures was caused by shallow foundation soil of very low strength, underlain by highly compressible clay in the area characterized by widely varying lithological facie.
Staff publications
Bearing capacity , Distress , Geotechnical investigation , Differential settlement , Research Subject Categories::TECHNOLOGY
Oloruntola, M.O. [] (2018). Investigation of causes of structural distress in Iwaya area, Lagos, southwestern Nigeria.