Subsoil Geotechnical Evaluation for the Design and Construction River Bridge Along Onuinyang Ikuano Road, Bende LGA, Abia State, Nigeria

This study investigates the ground condition and engineering properties of the subsurface soils along Onuiyang Ikuano Road in Bende LGA, Abia State, Nigeria using geotechnical method. The aim is to determine geotechnical parameters for the design and construction of the abutement and pier of a river bridge to link two sections of the road. The investigation adopted both field methods which included boring, soil sampling and SPT, and laboratory tests to determine moisture content, Atterberg limits, particle size distribution, soil shear strength parameters such as cohesion and internal friction angle. The results indicated three (3) distinct lithologic units with varied thickness. They are soft to medium brown lateritic clay at the top followed by a loose to medium dense, fine to medium sand. The third layer is a medium dense, fine to medium sand. The SPT N-values varied from 6 to 27 at various depths. The moisture content ranged from 11.9 to 37.4%. The liquid limit varied between 20 – 42% while the plastic limit is between 9 and 31%. For the shear strength parameters, cohesion ranges from 56 to 69 KN/m3 with corresponding frictional angle of 8o to 9o respectively. A pile foundation to be founded at 20.0m depth was recommended based on the geotechnical information of the soil and in-situ densities of the soil. Allowable load carrying capacities of the piles were computed to be between 600.2 and 646.2 KN for 450mm diameter pile, and 1050.9KN and 1128.6 KN for a pile of 600mm diameter respectively. The study highlights the critical role of geotechnical surveys in design of safe, resilient and sustainable civil structures. However, it is recommended that the foundation engineer should confirm the proposed capacities and eventually design the foundation based on the specific loadings.