GEOFORENSIC ANALYSIS OF RECENT BUILDING COLLAPSE IN PORTHARCOURT, NIGERIA

Abstract

Only recently, Port Harcourt witnessed four incidences of building collapse within a span of two months. The paper uses observation, field and laboratory testing and deductions to figure out the cause of the collapse. In order to explain the role of the foundation, a back-analysis of the load bearing capabilities of the sub-soil was carried out at the collapsed building sites using results of boring and cone penetration tests (CPT). This analysis indicated the allowable bearing pressures for Abacha Road, Tombia Street and Tourist beach sites as 80kPa, 50kPa and 30kPa respectively. In comparison with the loadings of the failed structures, these values of allowable bearing pressure were considered unsatisfactory with operational factors of safety less than 1 and significantly high values of consolidation settlement. On the contrary, the site at the old GRA with an allowable bearing pressure of 150kPa could not be explained by the incompetence of the foundation. This failure was probably caused by structural defects. Based on the spatial distribution of collapsed buildings and experience of soil variability in Port Harcourt metropolis, the area within the flood plain of the Ntawoba creek (from Abacha Road to Amadi Creek) and the reclaimed mangrove swamp can be designated as marginal lands, requiring ground improvement prior to foundation construction.