Geotechnical Basis for Building Instability and Failure: Case Study from Lagos, Nigeria

Abstract

The incessant occurrence and rise in the incidence of building failure and collapse with attendant loss of lives and property in Lagos (Southwestern Nigeria) in recent past has reached geometric proportions and is a source of national embarrassment. Hence, the need to investigate if any, the geotechnical basis as opposed to the commonly adduced reasons for recurrence became imperative. Vertical Electrical Sounding (VES), Cone Penetrometer Test (CPT), Boreholes and Standard Penetration Test (SPT) points were established strategically for in situ data acquisition and collection of disturbed and undisturbed soils for subsequent laboratory analyses. Integration of VES, CPT, Borehole and SPT results delineated maximum 4 layers of top soil, peat, organic clay and sand with significant thickness of near surface very low bearing capacity peat and organic clay underlying the unstable sections while stable section is underlain by near surface medium dense to dense sand with resistivity and bearing capacity high enough to support most engineering structures. Furthermore laboratory analyses also indicated presence of low shear strength, highly compressible soils with high plasticity of significant thickness underlying the unstable sections. Thus, it can be concluded that the instability and failures noticed is largely attributable to geotechnical and hence geological reasons.