Effect of motor oil contamination on geotechnical properties of over consolidated clay

The present study deals with the effect of motor oil contamination on the geotechnical properties of over-consolidated clay. Contamination effect and contamination duration are achieved by storing the clay samples in pressurized tank filled with motor oil under pressure of approximately 65 kPa which is almost equivalent to the overburden pressure that affected the clay at the field. Four parameters are considered to follow the contamination effect; Atterberg limits, unconfined compressive strength, coefficient of permeability, and compressibility characteristics. The experimental study reveals that the unconfined compressive strength is reduced by about 38% as compared to the control value (uncontaminated). The reduction remains for 6 months and declines furthermore attaining constant value. The contamination of the clay with motor oil entailed substantial microstructural changes: relatively loose packing of clay particles and their detachment from grain surface. The Atterberg limits are reduced during the first 3 months of contamination. They reached almost constant limits until the clay structure attained stability state. These limits remain constant for 24 months (experiment duration). The coefficient of permeability is significantly increase and exhibits direct proportion with duration of contamination up to 3 months. Oil contamination shows minor effect on over-consolidation ratio. Both compression and swelling indexes declare positive correlation with duration of contamination up to 6 months. These indexes reach almost double the control values. After the first 6 months of contamination, these indexes remain constant.