Geotechnical Assessment of Lateritic Soil for Subgrade and Sub-Base Applications in Road Construction: A Case Study from Akwa Ibom State, Nigeria

This study evaluates the geotechnical properties of lateritic soil from borrow pits in Ekit Itam II, Afia Nsit Atai II, and Ikot Ekpuk villages in Itu, Nsit Ibom, and Oruk Anam Local Government Areas, Akwa Ibom State, Nigeria, to assess its suitability for subgrade and sub-base applications in road construction. Laboratory tests, conducted in accordance with the Federal Ministry of Power, Works and Housing specifications, included particle size distribution, Atterberg limits, compaction characteristics, and California Bearing Ratio (CBR). The results demonstrate that the soils meet the required standards for road foundation layers. Specifically, the liquid limits were 28%, 34%, and 28%, with plastic limits of 17%, 21%, and 16%, and plasticity indices of 11%, 13%, and 12% for samples L1, L2, and L3, respectively. The maximum dry densities ranged from 1.97 g/cm<sup>3</sup> to 2.03 g/cm<sup>3</sup>, with optimum moisture contents of 8%, 9.89%, and 10.02%. CBR values for sub-base applications were 38.50%, 33.30%, and 65.40% (24-hour half-soaked) and for subgrade were 21.60%, 15%, and 40.60% (48-hour fully soaked). Particle size analysis revealed D10 values of 0.08-0.09 mm, D30 of 0.18-0.25 mm, and D60 of 0.30-0.45 mm, with coefficients of uniformity (Cu) of 3.33-5.63 and curvature (Cc) of 1.00-1.74, indicating poorly graded clayey sand (SC) soils under the Unified Soil Classification System (USCS) and A-2-6 under the AASHTO classification. These properties confirm the lateritic soil’s suitability for use as subgrade and sub-base materials, supporting sustainable road infrastructure development in Akwa Ibom State. The findings underscore the importance of thorough geotechnical assessments to ensure the quality and durability of pavement materials, contributing to improved regional connectivity and economic growth. Recommendations include ongoing research to characterize soil variability across borrow pits to guide material selection for construction projects.