Foundation Settlement in Reclaimed Mangrove Swamplands:ACase Study ofEastern Bypass, Port

Abstract

Abstract Useable land is scarce in the mangrove swamps of the Niger Delta. This is because it is underlain at the top by very soft to soft fibroitic silty and sandy clay (locally called Chikoko) and subject to diurnal submergence by tidal flow, thus making it difficult to develop without improvement. Reclamation by hydraulic sandfill is the commonest approach to transform such mangrove swamp areas into useable land but the ground response to sandfill placement and requirements for subsequent use are not fully understood. The purpose of this paper is to analyze the ground response to loading through settlement analysis of insitu CPT and laboratory data using the case study of the Eastern Bye-pass, PortHarcourt which was reclaimed in 3 phases, (1980-92, 1992-2000 and 2000-2020). The first was inspired by the necessity for a link road between Marine Base and Ogbunabali while the two subsequent phases were necessitated by strategic development needs. Reclamation involved the transformation of some 3 km2 mangrove swamp through the placement of approximately 2.5 m thick hydraulic sandfilling over the fibrotic and bioturbated silty and sandy clay soil rich in partially decomposed vegetal matter. Although 97% Consolidation settlement was to be achieved in 3 rd years, the road link was constructed before the end of the 3 year and has since been in satisfactory operational use, mainly due to the combined action of frictional bearing capacity, immediate settlement and drainage qualities of the river sand used as fill and also of the rapid settlement of the mangrove swamp soil occasioned by enhanced drainage from bioturbation.Abstract Useable land is scarce in the mangrove swamps of the Niger Delta. This is because it is underlain at the top by very soft to soft fibroitic silty and sandy clay (locally called Chikoko) and subject to diurnal submergence by tidal flow, thus making it difficult to develop without improvement. Reclamation by hydraulic sandfill is the commonest approach to transform such mangrove swamp areas into useable land but the ground response to sandfill placement and requirements for subsequent use are not fully understood. The purpose of this paper is to analyze the ground response to loading through settlement analysis of insitu CPT and laboratory data using the case study of the Eastern Bye-pass, PortHarcourt which was reclaimed in 3 phases, (1980-92, 1992-2000 and 2000-2020). The first was inspired by the necessity for a link road between Marine Base and Ogbunabali while the two subsequent phases were necessitated by strategic development needs. Reclamation involved the transformation of some 3 km2 mangrove swamp through the placement of approximately 2.5 m thick hydraulic sandfilling over the fibrotic and bioturbated silty and sandy clay soil rich in partially decomposed vegetal matter. Although 97% Consolidation settlement was to be achieved in 3 rd years, the road link was constructed before the end of the 3 year and has since been in satisfactory operational use, mainly due to the combined action of frictional bearing capacity, immediate settlement and drainage qualities of the river sand used as fill and also of the rapid settlement of the mangrove swamp soil occasioned by enhanced drainage from bioturbation.

Publication Info:

Author: Abam,T.K.S.1, Giadom, F.D.2, Kala-Otaji, E.D.3and Obrike, S.

Volume: 59

Issue: September

Published By: Journal of Mining and GeologyVol. 59(2) 2023. pp. 157 - 166, 2023-09-01