Abstract: To obtain the failure characteristics and failure mechanism of red soil slope in cyclic wetting-drying condition, physical model test was conducted in line with the similarity theory by monitoring the slope model for one year and a half. Results revealed that under drying condition, the generation of cracks on the surface of the red soil slope is related to water content; in particular, when water content is below 27.5%, cracks were generated on the surface of red soil; and with the decline of water content, the number and width of cracks experienced gentle increase, sharp increase and steady development in sequence. Under cyclic wetting and drying, cracks on red soil surface were generated, coalesced, and then regenerated; and with the increase of rainfall cycles, cracks developed towards the deep, correspondingly with a gradual increase in crack width and depth; surface water permeated along the cracks into the red soil layer at the bottom of slope, resulting in the argillation of red soil particles. Furthermore after one and a half years of cyclic wetting and drying, surface water permeated to the bottom of slope along two vertical cracks, and softened and disintegrated the slope from bottom to the top, finally gave rise to water conducting channels which induce large-scale landslides.

Key words: red soil slope, physical model test, cyclic wetting-drying condition, crack, softening and disintegration