UBAH, Samuel Uche

A good road network of a developing area such as Ekosodin community to major cities leads to rapid urban development. However, the erosion susceptible soil in the area has tasked highway and geotechnical engineers into research on improvement techniques on such problematic soil and still produce satisfactory pavement or foundation bases. Therefore, this study was focused on testing the effect of caustic soda additives on erosion susceptible soil in Ekosodin, Benin city, to improve its geotechnical properties. This study was achieved by collecting four soil samples from the study area, analysingthe soil specific gravity, particle size distribution, Atterberg limits, optimum moisture content, maximum dry density, cohesion, angle of internal friction, and California bearing ratio. Also, the effect of the caustic soda addition in 2%, 4%, 6%, 8% and 10% on these geotechnical properties were investigated and compared. Afterwards, the optimum percentage of caustic soda to give the highest soil strength based on the load bearing and subgrade capacity was determined. The final soil results, based on its index and engineering properties in its unstabilized form, showed an AASHTO class of A-6 and A-7-6 class soil which usual types of significant constituent materials are Clayey soil of more than 35% fine passing BS sieve No 200, with fair to poor subgrade rating in pavement design and a significant level of plasticity. However, the addition of caustic soda was analyzed to a maximum percentage of 10 on the Soil Atterberg limits, Compaction and California Bearing Ratio (CBR) test results, and the following was observed. A decrease in the liquid limit from 50.38% to 25.44% in soil samples at point 1; 39.66% to 25.49% in point 2; 50.59% to 26.20% in point 3; and 41.99% to 28.22% in point 4. Similarly, the plastic limit reduced from 25.53% to 11.47%, 20.12% to 10.96%, 21.18% to 14.22%, and 20.77% to 16.04% for soil samples at points 1, 2, 3, and 4 respectively. While the optimum moisture content decreased from their original values of 15.7%, 14.8%, 15.9%, and 14.8% to 13.30%,13.80%, 11.20%, and 10.30% for soil in points 1, 2, 3, and 4 respectively. Similarly, the angle of internal friction from their original values of 5.45°, 7.02°, 8.14°, and 6.49° to 3.75°, 5.54°, 7.06°, and 5.17° for soil in points 1, 2, 3, and 4 respectively. However, an increase in the maximum dry density from 1.63 g/cm3, 1.65 g/cm3, 1.63 g/cm3, 1.66g/cm3 to 1.79 g/cm3, 1.77 g/cm3, 1.80 g/cm3, and 1.79 g/cm3 respectively at the addition of the 10% caustic soda. Similarly, increased the cohesion from their original values of 32.0 kN/m2, 27.0 kN/m2, 31.0 kN/m2, and 32.0 kN/m2 to 38.60 kN/m2, 32.00 kN/m2, 38.04 kN/m2, and 37.86 kN/m2 for soil in points 1, 2, 3, and 4 respectively.Also, an increase in the California Bearing Ratio (CBR) was observed both in theunsoaked and soaked state to 23.45%, 22.99%, 26.00%, and 20.50% for soil in points 1,2, 3 and 4 respectively. The highest soaked soil CBR value of 26.0% was achieved at an optimum value of 10% caustic soda stabilization. Therefore, the chemical stabilization of caustic soda was recommended for erosion susceptible soil in Ekosodin as it improved the soil sample of the area from poor subgrade or foundation soil to a good load bearing and subgrade capacity soil for building and road construction.