Utilization of Nanosilica and Hydrated Lime to Improve the Unconfined Compressive Strength (UCS) of Gas Oil Contaminated Clay

Crude oil and petroleum products can pollute soils during refining, transportation and operation processes. Because of physicochemical effects and reactions between these fluids and soils, geotechnical behavior and properties of soils change. Since these changes are mostly adverse, improvement and treatment of contaminated soils and sediments are necessary in many geotechnical projects and works. In present research, using lime as a traditional additive and nanosilica is considered for treating of gas oil contaminated clay. The polluted specimens were prepared by mixing the soil with gas oil in amounts of 0, 3, 6 and 9% by dry weight. The contaminant increased liquid limit (LL) and plastic limit (PL), and reduced maximum dry density (MDD) and optimum moisture content (OMC) of the soil. Unconfined compressive strength (UCS) of the soil showed an initial increase in 3% of contamination and then a decrease for the heavily contaminated samples (i.e., gas oil content greater than 3%). After adding 0, 1, 2 and 3 weight percent of lime and nanosilica, both independently and together; LL, PL, OMC and UCS of the samples increased and MDD of the treated soils decreased. Compared with lime and nanosilica, the mixture of them was considered more efficient in improving the UCS. By adding 3% of nanosilica-lime mixture and increasing curing time, considerable UCS gains occurred.