Abstract
Variations based on the effects of curing time and environmental exposures on the geotechnical characteristics of some crude oil contaminated soils were investigated. 2 to 10% by weight of crude oil was added to soils as a simulation of contamination. The contaminated soils were cured under room temperature (unexposed) as well as outside in the open air (exposed) for 21, 63 and 189 days. Geotechnical, geochemical and mineralogical analyses were carried out on the contaminated and uncontaminated soil samples. Results indicate that for the unexposed soils, the LL and PL increased as crude oil concentration (COC) increased up to 4%, above which both decrease. But the reverse was the case for PI after curing for 21 days. With increasing curing time to 63 and 189 days, LL and PL both increased with increase in COC while PI decreased. The UCS increased with increase in oil content up to 4%, but decreased as oil content increased above 4%. Furthermore, UCS decreased with increase in curing time. Across all curing periods, MDD increased upon addition of crude oil up to 4%, thereafter it decreased with increase in COC. The hydraulic conductivity decreased with increase in COC and curing time. For the exposed soils, LL, PL and PI all increased upon addition of crude oil up till 4% before decreasing as the amount of oil increased above 4% for the curing duration of 21 days. For 63 and 189 days, LL and PL decreased while PI increased. Maximum dry density (MDD) showed same variation trend in exposed soils similar to that shown by the unexposed soils. Hydraulic conductivity increased with increase in COC and curing time. Thus, crude oil is observed to be capable of altering the geotechnical properties of soils exposed to it. Furthermore, contaminated soils exposed to the open air and longer curing time were significantly modified than the unexposed variant and with reduced exposure time.
 Keywords: Geotechnical variation, Contamination, Curing environment, Curing time, Exposure
Highlights
Hydrocarbon pollution of soil can occur in several ways, from natural seepage in areas where petroleum is found in shallow reservoirs, to accidental spillage of crude oil
The liquid limit (LL), and plastic limit (PL) increases as COC increased up to 4%, above which both decrease, but the reverse was the case for plasticity index (PI) after curing for 21days
Maximum dry density (MDD) increased upon addition of crude oil up to 4%, thereafter it decreased with increase in amount of oil
Summary
Hydrocarbon pollution of soil can occur in several ways, from natural seepage in areas where petroleum is found in shallow reservoirs, to accidental spillage of crude oil. Evgin et al (1992) performed a series of triaxial tests on contaminated and uncontaminated clean sands with results showing that the oil-saturated samples drastically reduced the friction angle for loose and dense samples while it apparently increased the volumetric strain. These findings suggested that settlement of footing would increase as a result of oil contamination. Investigations into the effect of crude oil on geotechnical properties of sandy soil and clay by Khamehchiyan et al (2007) showed that the Atterberg limits decreased with the increase in oil percentage while increase in oil content caused decrease in maximum dry density, optimum water content, porosity and shear strength. A corresponding increase in bulk density with increase in sorption time was observed
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