Comparison of the Geotechnical Properties of Lateritic Soils of Borrow Pits for Road Construction in Ado Ekiti

Abstract

Lateritic soils are key materials in road construction across tropical regions, but their performance varies based on their geotechnical properties. This study analyzes the geotechnical properties and characteristics of lateritic soils from selected borrow pits in Ado Ekiti, Nigeria, to determine their suitability for subbase and subgrade applications. Four borrow pits, labeled A to D, were randomly selected, and twelve undisturbed soil samples (three from each pit) were collected for laboratory testing. The tests include natural moisture content, specific gravity, grain size distribution, Atterberg limits, permeability, compaction, California Bearing Ratio (CBR), unconfined compressive strength (UCS), and triaxial test. Soil samples from Borrow Pit A, identified as Silty Sand (SM) and classified as A-2-4, showed the highest Maximum Dry Density (1750–1753 kg/m³), low Optimum Moisture Content (12%–14%), fines content of 12%, adequate permeability (2.0 × 10⁻⁵ to 2.2 × 10⁻⁵ cm/s), and unsoaked CBR values of 70%–75%, making them ideal for subbase applications. Borrow Pit B soil samples, categorized as Clayey Sand (SC) and A-2-6, had moderate MDD values (1650–1660 kg/m³), permeability between 1.2 × 10⁻⁵ and 1.4 × 10⁻⁵ cm/s, unsoaked CBR values of 58%–60%, and shear strength of 205–210 kPa, making them suitable for improved subgrades or low-traffic subbases. Borrow Pits C and D, classified as Low Plasticity Clay (CL) under USCS and A-6 and A-7-6 under AASHTO, had MDD values between 1500–1551 kg/m³, fines content of 20%–30%, permeability between 0.4 × 10⁻⁵ and 0.1 × 10⁻⁵ cm/s, unsoaked CBR values below 42%, and shear strength of 180–192 kPa, making them more appropriate for subgrade applications. The study concludes that Borrow Pit A is the most suitable for subbase layers, while Borrow Pits B, C, and D require stabilization, such as lime or cement treatment, to improve their strength and plasticity properties.