Abstract: Taking the expansive soil in Guangxi as the research object, considering the influence of vegetation, field seepage test and mechanical test of vegetation root system are carried out. Based on the results of test, numerical simulation work on vegetation protection mechanism of cut slope is put forward. The results show that there are two different aspects to maintain the stability of the expansive soil slope, which are vegetation root reinforcement effect and vegetation evaporation and transpiration; and there is a successive process in rainfall to perform the protection behavior for vegetation root reinforcement effect and vegetation evaporation and transpiration. The reinforcement effect of the vegetation root enhances the strength of the soil. Vegetation evaporation and transpiration prevents the soil strength decay. Meanwhile, it is found that the soil with the vegetation covered should adopt different permeability curves in the wetting and dehumidifying process. The vegetation protection is very weak after construction because the roots will grow for a long time. So, study of the vegetation root mechanical characteristics in growth period is of great significance. Research result of this project has important reference for the development and application of design and construction for vegetation protection of expansive soil cut slope.

Key words: expansive soil, cut slope, vegetation, root system, atmosphere action