Abstract: In order to investigate the cause of surface spalling of highway slope, we extracted Q₃ undisturbed loess at K700+200 of a highway. In the investigation, scanning electron microscope (SEM) was used to detect prepared samples after 0, 1, 5, 10 and 20 dry-wet cycles and freeze-thaw cycles respectively. Changes of SEM images after different dry-wet cycles and freeze-thaw cycles were compared and analyzed quantitatively. Soil skeleton as well as pore morphology are analyzed either by IPP image processing software in our research. Change rules of surface porosity, average pore diameter and pore size fractal dimension after different times of dry-wet cycle and freeze-thaw cycle are obtained therefore, and variations of soil microstructure after different dry-wet cycles and freeze-thaw cycles are quantitatively analyzed. Results coming from our investigations indicate that:Both dry-wet cycle and freeze-thaw cycle have great influence on soil microstructure. It is revealed further that the surface spalling of loess slope is closely related to dry-wet cycle and freeze-thaw cycle.

Key words: dry-wet cycles, freeze-thaw cycles, scanning electron microscopy test, microstructure