Analytical Investigation of Laterite Soil Improvement for Use as Road Sub-Base Material in South South Nigeria

Laterite soils in South South Nigeria exhibit variable geotechnical properties that frequently require improvement before use as road sub-base material, yet systematic analytical investigation of improvement treatment options calibrated for the regional laterite characteristics is limited in the published literature. This study analytically investigates lime, cement, and lime-cement combination stabilisation of laterite soils from three borrow pit sources in Rivers, Delta, and Bayelsa States. Soil samples underwent comprehensive geotechnical characterisation (Atterberg limits, gradation, specific gravity, and compaction characteristics). Stabilisation treatments using lime (2, 4, 6, 8 percent), cement (3, 6, 9 percent), and lime-cement combinations (2+3, 4+3 percent by dry weight) were prepared at optimum moisture content and cured for 7 and 28 days. California Bearing Ratio, Unconfined Compressive Strength, Indirect Tensile Strength, and swell tests were conducted. Results indicate that lime treatment alone is most effective for reducing plasticity in high-PI soils but produces lower CBR improvement than cement. The 6 percent cement treatment achieves the most consistent 28-day CBR improvement (from 14 to 68 percent), exceeding the 30 percent road sub-base specification. Combined lime-cement treatment shows the best performance in highly plastic soils where cement alone shows modest improvement. An optimum treatment selection framework is developed based on initial soil plasticity and target performance. Adoption by South South Nigerian state road agencies is recommended.

Keywords: laterite stabilisation, road sub-base, lime treatment, cement stabilisation, South South Nigeria