Effects of clay content on the volumetric behavior of loess under heating-cooling cycles

Although numerous studies have been carried out on investigating thermal volume changes in different soils, limited attention has been paid to loess. This study aims to investigate the effects of clay content on the deformation of loess under heating-cooling cycles. Three soils with different clay contents (i.e. SA: 7%; SB: 13%; SC: 35%) were prepared with loess collected in situ through the sedimentation method. The soil volume changes were measured under heating-cooling cycles by using a thermal invar oedometer. To interpret the experimental results, X-ray diffraction (XRD) and scanning electron microscope (SEM) tests were conducted to identify the composition and microstructure of tested soils, respectively. The results show that the plastic axial strains of SA, SB, and SC accumulate to a certain level with the increasing number of heating-cooling cycles. At the stable state, the plastic axial strain of SC is 264% and 52% larger than those of SA and SB, respectively. On the other hand, the linear thermal expansion coefficient of SC is 66% and 20% larger than those of SA and SB, respectively. As evidenced from the XRD test, the clay in loess mainly contains kaolinite, chlorite, and illite, while the composition of silt is dominated by quartz. The clay minerals are more sensitive to thermal fluctuations than quartz because of the electrical double layer. SC, whose clay content is deliberately enhanced, exhibits a larger plastic axial strain and linear thermal expansion coefficient than do SA and SB.