Reliability analysis of natural soil slope considering the effect of vegetation

Abstract

Over the past decades, effects of climate change including intense rainfalls have resulted in many slope failures. Research activity in understanding the mechanism of rainfall-induced landslides has recently focused on the probability of slope failure. In addition, the effect of root reinforcement on slope stability has been recognized especially for vegetated slope. In this research, a reliability analysis of soil slope considering the effect of vegetation is performed. The spatial variability of soil properties and vegetation is assumed to be modelled as a stationary random field in slope reliability analysis. The shear strength parameters of soil and root cohesion quantified by statistical characteristics are considered. Two natural slopes are selected as case studies. Firstly, a case study of shallow failure located on sandstone slopes in Japan is used to verify the analysis framework. A series of seepage and stability analyses of an infinite slope based on random fields is conducted. The results confirm that a probabilistic analysis can be efficiently used to qualify various locations of failure surface caused by spatial variability of soil shear strength for a shallow infinite slope failure due to rainfall. Secondly, a field monitoring on a residual soil slope in Thailand is modelled. The soil water characteristic curve and the saturated permeability measured from the tests are used in the transient seepage analysis. The results of pore water pressure are compared with the monitored values from the site. The shear strength of soil from the root cohesion is modelled for vegetated soil slope. Factors of safety calculated from transient seepage and slope stability analysis are compared between vegetated and non-vegetated cases. In addition, the effect of spatial variability of root cohesion on probability of slope failure is considered. The results exhibit that a uniform distribution of root can significantly contribute to slope stability especially for the vegetated slope.