Evaluation of the stability of vegetated slopes according to layout and temporal changes

Vegetation in slopes can effectively improve slope stability. However, it is difficult to estimate the effects of vegetation on slope stability because of variations in plant species and environmental conditions. Moreover, influences of plant growth on slope stability change with time, resulting in changes in the safety factor. This study was conducted to evaluate the stability of vegetated slopes with time and investigate the effects of different layouts of plant species on slope stability. Here, we used a plant growth model and slope stability analysis to build an evaluation model. To accomplish this, one species of tree, shrub and grass was chosen to set six layout patterns. A slope with no vegetation served as a control. The safety factors of the seven slopes were then calculated using the developed evaluation model and differences in the safety factors of slopes were compared and discussed. The slope vegetated with Platycladus orientalis reached the most stable state at the age of 60 years. Shrub slope (Vitex negundo) had the maximum safety factor after 20 years. Overall, the safety factor of vegetated slopes increased from 12.1% to 49.6% compared to the slope with no vegetation. When wind force was considered, the safety factor value of the slope changed from 3.5% to 43.5%. Vegetation mixtures of trees and grasses resulted in the best slope stability. Planting grasses on slopes can improve slope stability of trees to a greater degree than that of slopes with shrubs in the early stage of growth.