Influence of Oil Contamination on Geotechnical Properties of Basaltic Residual Soil

Abstract

Problem statement: Oil contamination due to accidental spillage or leakage brings hefty damage to the environments. It percolates steadily into subsurface environments and contaminates the soil and water system. Hydrocarbon contamination has not just affected the quality of the soil but will also alter the physical properties of oil-contaminated soil. Approach: This study presented the geotechnical properties of oil-contaminated soils as well as uncontaminated soils for comparison. Testing programs performed on the studied soils included basic properties, Atterberg limit, compaction, permeability and unconsolidated undrained triaxial tests. The base soils used were originated from weathered basaltic rock of grades V and VI. Soil samples were artificially contaminated with 4, 8, 12 and 16% oil of the dry weight of based soils. Results: The results showed that the oil contamination decreased the liquid limit and plastic limit values for both grades of weathered soils. For soil grade V, the decrease in plastic limit and liquid limit were represented by 21 and 39%, respectively. Meanwhile, for soil grade VI, the drop was significantly high for liquid limit (39%) and lower for plastic limit (19%) if compared to soil grade V. The oil-contaminated soils also indicated a lower Maximum Dry Density (MDD) and optimum water content if compared with uncontaminated soils. The MDD for soil grade V and VI decreased from 1.67-1.50 and 1.60-1.55 g cm^-3, respectively. The OMD values dropped from 23.5-17.5% for soil grade V and 23.0-16.5% for soil grade VI when oil contents were increased. A reduction in permeability was observed as a result of the oil contamination. The permeability of soil grade V and VI decreased from 3.74-0.22 and 2.65-0.22 cm sec^-1, respectively. In terms of undrained shear strength, C_u was clearly affected by the increase in oil content in contaminated soils. Both soil grades showed stress dependant behavior with a brittle mode of failure. The C_u values for uncontaminated soils of both grades were 126 and 106 kPa and then dropped to very close values of 35 and 32 kPa at oil content of 16%. Conclusion: The results showed that the addition of oil has adverse effects to the geotechnical properties of the studied residual soil. Contaminated residual soils might be used for geotechnical purposes and these results will benefit to engineers or decision makers in recycling or re-using of contaminated soils.