Use of nanoscale zero-valent iron and nanoscale hydrated lime to improve geotechnical properties of gas oil contaminated clay: a comparative study

Soil stabilization using lime has been long used to improve geotechnical characteristics of soil for civil engineering purposes. Unlike lime, as far as known to the authors, there is no specific research for soil improvement by zero-valent iron. In this study nanoscale zero-valent iron (NZVI) particles and nanoscale hydrated lime (NHL) have been used to determine their effects on Atterberg limits, compaction properties, unconfined compressive strength (UCS) and shear strength parameters (c and phi) of a gas oil contaminated clay soil. To determine the optimal reaction time and NZVI dosage, percent of total organic carbon in the contaminated soil with 9 % of gas oil was measured. From experimental data, optimum reaction time and NZVI dosage were 24 days and 5 %, respectively. Then, the contaminated samples were prepared by mixing the soil with gas oil in amounts of 0, 3, 6 and 9 % by dry weight. The results showed a decrease in UCS, maximum dry density, optimum moisture content and internal friction angle and an increase in liquid limit (LL), plastic limit (PL) and cohesion. Finally, all contaminated specimens were mixed with 5 % of NZVI. After 24 days an increase in UCS, maximum dry density, optimum water content and shear strength parameters was seen. In addition, a decrease in LL and PL was observed. On the other hand, adding 5 % of NHL to the contaminated soil increased UCS, shear strength parameters, LL, PL, optimum moisture content and decreased plasticity index and maximum dry density of the soil after 24 days.