Effects of crude oil contamination on geotechnical properties of sand-kaolinite mixtures

Abstract

Abstract In this study, a series of laboratory tests were performed to investigate the interaction between crude oil, clay minerals, and sand particles in contaminated soils and the effect of crude oil on the engineering properties of sand-kaolinite mixtures with different weight ratios of clay to sand was evaluated. Mixtures with a weight ratio of 10%, 30% and 50% kaolinite to sand contaminated with different contents of crude oil (including 0%, 4%, 6% and 8% by dry weight of soil) have been considered. Standard compaction, unconsolidated undrained triaxial, permeability, pH, and water holding capacity (WHC) tests have been conducted on the clean and contaminated specimens at the same dry density. In addition, Scanning Electron Microscope (SEM) has been used to identify the microscopic interactions between crude oil, kaolinite and sand particles. The results show that due to an increase in contamination, the maximum dry density, optimum water content, permeability and pH values were decreased. Different ratios of clay/sand had a significant effect on WHC value and soil shear strength parameters in the presence of the crude oil. While in the sandy specimens with low clay quantity, the addition of crude oil decreased the internal friction angle, in the specimens with high clay quantity, the angle of friction increased. SEM images showed that crude oil contamination caused aggregation of clay particles and a flocculated structure with more macropores. The findings of this paper can clarify the hydro-chemo-mechanical properties of a wide range of soils and help in geotechnical designs of contaminated soils.