Mechanical Behavior of a Hardened Oil–Silica Sand Composite

To evaluate the mechanical behavior of a potential soil stabilizer (a hardening tung oil) with a coarse silica sand, the strength characteristics at both peak and critical state and the stress–dilatancy relationship were investigated on both natural sand and the hardened oil–sand composite. Tung oil concentration and heating duration varied from 3% to 5% and 1 to 3 days, respectively. Triaxial compression tests were performed under effective confining pressures ranging from 50 to 800 kPa, in both drained and undrained conditions. The results revealed a stress-dependent behavior. Compared to natural sand, the peak strength of the hardened oil–sand composite was enhanced at a confining pressure of 50–200 kPa, decreasing at higher confining pressures (400–800 kPa). The stress ratio at critical state of the composite decreased at low confining pressures (50–200 kPa), followed by an increase at high confining pressures (200–800 kPa). The peak strength envelope exhibited a similar stress-dependent trend. A scanning electron microscope equipped with energy dispersive X-ray spectrometry (SEM-EDS) and thermogravimetric analysis (TGA) were used to identify the mechanisms controlling the behavior, by measuring the ratio of silicon (Si) to carbon (C) on the particle surface, and the weight loss of tung oil, respectively. Under high confining pressures (>200 kPa), coating abrasion was associated with an increasing ratio of Si to C and a decreasing weight loss of tung oil. This peculiar stress-dependent behavior of the hardened oil–sand composite was consistent with the recovery of the stress ratio at critical state.