Effect of Thermal Treatment on the Expansion Characteristics of the Diesel-Contaminated Soil and Its Mechanism

Adopting the expansive soil in Nanning, China, as the pollution-free background soil, and 0# diesel as the petroleum hydrocarbon pollutant, the effect of thermal treatment on the expansion characteristics of contaminated soil by diesel was studied. X-ray diffraction (XRD), mercury intrusion porosimetry method (MIP), scanning electron microscopy (SEM), and gas chromatography-flame ionization detection (GC-FID) were adopted in a study of the effect mechanism. The results reveal that at a constant diesel content, the steady-state no-load expansion ratio (Steady ER) of the thermal treated diesel-contaminated expansive soil (TT-ES) decreases with increasing heating temperature, and the expansion time history curve changes from a three-stage shape to a straight-line shape. The XRD test results show that the content of illite, which determines the expansion characteristics of the TT-ES, has not changed during the thermal treatment and cannot be used to explain the decrease of expansion characteristics of TT-ES. However, the change of its crystal structure can have an impact on the expansion characteristics. Within the heating temperature range from 500 similar to 800 degrees C, the cation exchange capacity decreases, which reduces the hydration reaction of the TT-ES, thereby decreasing the Steady ER. Within the full heating temperature range, the soil structure affects the time history curve shape and the Steady ER. When the heating temperature remains constant, the larger the diesel fuel amount was, the lower Steady ER. Similarly, the decrease in cation exchange capacity due to the incorporation of diesel oil and the change of the soil structure reduce the Steady ER.