Lime Stabilization of Vermi-Remediated Crude Oil Contaminated Lateritic Soil for Road Base Material

Abstract

This research is aimed at stabilizing vermi-remediated crude oil contaminated soil using lime for application as highway base material. 250kg of lateritic soil sample was contaminated with crude oil at a rate of 75cl of crude per 10kg of the soil sample and mixed with 1000 ml of water. The mixture was allowed for a period of one month for full saturation. The total petroleum hydrocarbon (TPH) present in the soil was then determined as 4500mg/kg. Atterberg test: liquid Limit (LL), Plastic Limit (PL) and Plasticity Index (PI) were determined as 39.5, 28.8 and 10.7 respectively. The optimum moisture content (OMC) for British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH) were 18.87, 17.18 and 15.78 respectively whereas the maximum dry content (MDD) was 1.63, 1.66 and 1.69Mg/m3 respectively. The unsoaked California Bearing Ratio (CBR) values for BSL, WAS and BSH were 4.45, 5.45 and 9.05% respectively whereas the soaked values were 4.75, 4.68 and 8.65% respectively. The unconfined compressive strength result for BSL WAS and BSH at 7 days curing were 182.7, 158.1 and 254.6kN/m2 respectively. The values for 14, 21 and 28 days followed the same pattern. The sample was then vermi-remediated with earth worm species (Eudrilus Eugeniae) at 400 worms per 200kg of soil for a period of one month after which the TPH content in the soil was determined as 3300mg/kg. The sample was then stabilized with lime at 2%, 4%, 6% and 8% respectively and the following results were obtained. Atterberg test: LL, PL and PI at 0% lime stabilization were determined as 54.0, 32.3 and 21.7 respectively, at 2% were 46.5, 29.3 and 17.2 respectively, at 4% were 56, 30 and 26 respectively, at 6% were 44.5, 11 and 33.5 respectively, at 8% were 58.0, 13.0 and 45.0 respectively. The shrinkage limit for all samples was 11%. The specific gravity for lime stabilized samples was also determined as 2.4 except at 6% which was 2.3. The optimum moisture content (OMC’s) for BSL, WAS and BSH at 2% lime admixture, were 20.38,19.74 and 16.55 respectively the values for 4, 6 and 8% followed same pattern. The MDD’s at 2%, were 1.61, 1.79 and 1.8 respectively and the same increasing pattern was observed for 4,6 and 8%. The unsoaked CBR values for BSL, at 2%, 4%, 6% and 8% lime admixture were 4.45, 21.47, 41.09 and 39.50 respectively. whereas the soaked values were 4.14, 19.27, 37.34 and 52.82 respectively. the same pattern of increment in strength with admixture was observed for WAS and BSH. The unconfined compressive strength result for BSL at 7 days curing at 2%, 4%, 6% and 8% lime admixture were 127.1, 234.1, 101.8 and 90.7 kN/m2. The same pattern was observed for 14- and 28-days curing period. The results show that lime is quite effective in stabilizing vermi-remediated crude oil contaminated soils at 8% admixture.