Volume 20, Issue 54, July - December, 2023

Geotechnical properties of foundation sub-soils in part of Niger delta, Yenagoa of Bayelsa State

Udom GJ, John PN

Department of Geology, University of Port Harcourt, Nigeria

ABSTRACT

The study was carried out with the aims of determining the stratification and geotechnical characteristics of foundation sub-soils underlying in six parts in Yenagoa local Government Area, Bayelsa state. Six boreholes were drilled in the six locations to a maximum depth of 20.25m. Laboratory tests and analysis were carried out on representative soil samples. Soil profiles were delineated followed by determination of their index and mechanical properties, including Atterberg limits, particle sizes distribution, undrained shear strength, shear box test and consolidation coefficient. Upper Silty clay horizon (0.0-5.25m thickness) very soft to firm for Yenagoa study areas, Medium silty clay horizon (0.75 to 1.5m thickness) soft to firm Yenagoa study areas, low clayey sand horizon (0.75 to 1.5m thickness) soft Yenagoa study areas, peaty clay (1.0m thickness between 3.0-4.0m) soft Igbogene Yenagoa, upper sand horizon (3.0m thickness) silty sand Etegwe town Yenagoa, lower sand horizon (13.5 to 18.0m) silty sand to fine to medium appear in all the boreholes in Yenagoa. Yenagoa sub-soil show low to high plasticity (CL-MH) according to unified soil classification system. From the results it shows that raft foundation is more economical in the six towns study areas of Yenagoa with Allowable bearing capacity of the upper clay layer ranges from 23-128KN/m². In view of the significant variations in the stratification and engineering geological index properties of the soil in the six towns in Yenagoa. However, the 1.0m thick peat embedded between 3.0m and 4.0m will great increase the compressibility of this clay. Pile foundation is recommended, considering the anticipated load and the very high compressibility of peat under imposed load. Piles should be straight-shaft, closed-ended steel pipe piles and driven into the medium dense sand. Straight shaft closed pipe piles were calculated for all the studies areas with diameter 305, 356, 406 and 610mm for the deep foundation for various study areas. Pile load test should be carried out on all piles to confirm working load and estimated settlements.

Keywords: Geotechnical index properties, Stratification, Allowable bearing capacities, pile foundation, Yenagoa

Indian Journal of Engineering, 2023, 20(54), e28ije1661

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DOI: https://doi.org/10.54905/disssi/v20i54/e28ije1661

Published: 6 July 2023