The effect of nanosilica on the compressibility, permeability, and mechanical properties of oil-contaminated soil

Oil pollutants (OPs) are among the most widespread soil contaminants and are known to severely impair soil compressibility, permeability, and mechanical performance. However, most studies have focused on a single oil pollutant and have not systematically identified which type causes the most severe deterioration of the soil’s hydraulic and consolidation behavior. In addition, the multifunctional role of nanosilica (NS) in simultaneously controlling compressibility, permeability, contaminant migration, and freeze–thaw (F-T) durability in oil-contaminated soils (OCSs) remains insufficiently understood. To address these gaps, one-dimensional consolidation and falling-head permeability tests were conducted to identify the oil pollutant causing the greatest adverse changes in soil behavior. The soil contaminated with that specific pollutant was subsequently stabilized using NS at dosages of 1%, 2%, and 3% by dry weight of soil. Supplementary laboratory experiments, including California Bearing Ratio (CBR), total petroleum hydrocarbons (TPH), and F–T durability tests, were performed on the stabilized specimens. The findings revealed that, among the four investigated pollutants (used motor oil, crude oil, diesel, and kerosene), kerosene caused the most significant increase in permeability and compressibility. Oil pollutants alter soil structure by increasing interparticle spacing and coating soil particles, thereby reducing water adsorption, accelerating drainage, and increasing compressibility and permeability. Conversely, NS improves soil structure through pore filling and viscous gel formation that bonds clay particles, thereby reducing pore space and lowering compressibility and permeability by up to 72% and 93%, respectively. NS also limits oil mobility, achieving up to a 20% TPH reduction and markedly enhancing F–T durability.