We performed a series of laboratory experiments using a large-scaled rainfall simulator and the stability analyses, in order to obtain the quantitative evaluations of the effects of vegetation on a face of slope. As the results of the experiments, we could obtain the quantitative relationship between a intensity of rainfall and a ratio of partial interception loss by vegetation, and also the evaporation and evapo-transpiration ratios could be calculated out from the observed weighing data. Based on the suctions measured during the experiments, the vertical distribution of soil-moisture could be numerically calculated, so that, the time-dependent slope model was represented by the obtained moisture distribution of each time-step, using the assumed relationship of the saturation degree and the corresponding shear strength. After the stability analyses were carried out against these slope models, the time-dependent changes of factors of safety were compared with the obtained evapo-transpiration ratios to exam the correlation of stability and water-uptake by vegetation. It was pointed out that the abilities of vegetation to intercept rainwater partially and to dry the soil as uptake can contribute stability of slope even partially depending on the meteorological situation and initial condition of soils. Finally, we could indicate the effects of vegetation on slope quantitatively as the stability of slope during/after rainfall through the experiments and analyses.
Earth structures are often applied for construction works of infrastructures, and actually often constructed at the sites along railways in Japan. For these structures, the surface treatment on the face of a slope should be required to prevent surficial sloughing and erosion by surface runoff. Depending on the circumstances surrounding the interested railway sites, the aesthetic impression for the public also tends to result in giving a high advantage to the choice of the vegetation as a surface treatment.