Abstract
Abstract Although numerous studies have been paid much attention to rainfall-induced instability of multilayered slopes, the interface between layers is generally considered to be “zero thickness”, and the layer transition zone between layers is neglected. In this study, the influence of the layer transition zone on the rainfall-induced instability of multilayered slope was investigated. A model was developed to simulate the rainfall infiltration process, the distribution of pore water pressure, and the stability of multilayered slope by coupling the unsaturated seepage model and the slope stability analysis method. Based on the analysis of the multilayered slopes with the different thickness ratios of the layer transition zone, a method for determining the critical thickness of the layer transition zone was proposed. The results showed that the layer transition zone had a significant influence on the stability of multilayered slope. It was found that the presence of the layer transition zone in the multilayered slope reduced the hydraulic conductivity of the slope and increased the rate of formation of transient saturated zone, which contributed to excess pore water pressure at the toe of the slope. The analysis of the local factor of safety (LFS) showed that when the thickness ratios of the layer transition zone were between 2.5% and 5%, the corresponding hydraulic conductivity of the slope decreased by 1%-2.5% and the maximum failure area of the slope during the rainfall was 25% of the slope. Our study highlighted the importance of the layer transition zone for the rainfall-induced instability of the multilayered slope.
Highlights
Landslides are serious geologic hazards in mountainous regions and are usually triggered by the rainfall events
Since the initial distribution of water content in the multilayered slope has a significant influence on the evolution of water content, in this study, eight multilayered slopes with different thickness ratios of the layer transition zone and one multilayered slope without the layer transition zone were established under a daily rainfall of 1.64 mm/d for 10 years to obtain the initial distributions of water pressure and water content
After t = 9 h, there is little difference from the transient saturated zone in both the multilayered slopes with and without the layer transition zone. This indicates that the influence of the layer transition zone on transient saturation zone is mainly reflected in the early stage of rainfall, while it is weak in the late stage of rainfall
Summary
Landslides are serious geologic hazards in mountainous regions and are usually triggered by the rainfall events. Using the upper bound limit analysis, a method for calculating the stability numbers for multilayered slopes was proposed [6], where it was assumed that the failure surface is a combination of different logarithmic spiral arcs with a common focus This method ensures the kinematic admissibility of the collapse mechanism with respect to the rigid rotation of the bounded soil mass about the focus of the logarithmic spiral. Previous studies [9, 10] modified the traditional infiltration model and numerical method for slope stability to analyze the temporal and spatial evolution of soil water content and pore water pressure during the rainfall infiltration.
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