Soil moisture storage and hillslope stability

Abstract

Abstract.Recently, we presented a steady-state analytical hillslope stability model to study rain-induced shallow landslides. This model is based on kinematic wave dynamics of saturated subsurface storage and the infinite slope stability assumption. Here we apply the model to investigate the effect of neglecting the unsaturated storage on the assessment of slope stability in the steady-state hydrology. For that purpose we extend the hydrological model to compute the soil pore pressure distribution over the entire flow domain. We also apply this model for hillslopes with non-constant soil depth to compare the stability of different hillslopes and to find the critical slip surface in hillslopes with different geometric characteristics. In order to do this, we incorporate more complex approaches to compute slope stability (Janbu's non-circular method and Bishop's simplified method) in the steady-state analytical hillslope stability model. We compare the safety factor (FS) derived from the infinite slope stability method and the more complex approach for two cases: with and without the soil moisture profile in the unsaturated zone. We apply this extended hillslope stability model to nine characteristic hillslope types with three different profile curvatures (concave, straight, convex) and three different plan shapes (convergent, parallel, divergent). Overall, we find that unsaturated zone storage does not play a critical role in determining the factor of safety for shallow and deep landslides. As a result, the effect of the unsaturated zone storage on slope stability can be neglected in the steady-state hydrology and one can assume the same bulk specific weight below and above the water table. We find that steep slopes with concave profile and convergent plan shape have the least stability. We also demonstrate that in hillslopes with non-constant soil depth (possible deep landslides), the ones with convex profiles and convergent plan shapes have slip surfaces with the minimum safety factor near the outlet region. In general,Correspondence to: A. Talebi (ali.talebi@wur.nl) when plan shape changes from divergent to convergent, stability decreases for all length profiles. Finally, we show that the applied slope stability methods and steady-state hydrology model based on the relative saturated storage can be used safely to investigate the relation between hillslope geometry and hillslope stability.

Datos De Precipitación Con El Modelo HSB Para Pronóstico De Deslizamiento De Suelos Superficiales

“…Las curvas de la FIGURA 4 se obtuvieron a partir de la ecuación 8, al considerar γ m = 1000 Kgm -3 , γ s = 1600 Kgm -3 y γ b = 600 Kgm -3 , siendo respectivamente el peso específico del agua, saturación y boyante (Talebi et al, 2007). Para este escenario se encuentra estable la ladera a lo largo del perfil para los periodos continuos de precipitación.…”

“…Un método para calcular el factor de seguridad en una pendiente infinita con una zona no saturada fue propuesta por Talebi et al (2007Talebi et al ( , 2008. Se asume que el nivel freático, el peso unitario de húmedo y la cohesión del suelo dependen de la coordenada x.…”

Seepage and slope stability modelling of rainfall-induced slope failures in topographic hollows

“…A number of studies, similar to this study, have linked slope hydrology to instability mechanism in the topographic hollows (Sidle 1987;Montgomery & Dietrich 1994;D'odorico & Fagherazzi 2003;Talebi et al 2007). Some monitoring studies have discussed the response of soil in a topographic hollow such as variation in subsurface run-off, porewater pressure, and temperature during a heavy rainstorm (Fannin & Jaakkola 1999;Uchida et al 2003).…”

Application of a probabilistic model of rainfall-induced shallow landslides to complex hollows

“…This is called the event-limited regime. Hence, it can be concluded that hollow geometry is an important control on subsurface flow response Hilbert et al, 2004) and this process affects slope stability (Talebi et al, 2007). Figure 2 shows long term simulations of deposit thickness evolution in the four hollows (from top to bottom) and illustrates how shallow landsliding occurs when the soil thickness (D) ranges between D cr and D max .…”

“…From the topography view point, in most models of slope stability only the slope angle is considered. Although slope gradient is an important factor in landslide initiation, other geometric characteristics (such as profile curvature and plan shape) also control the hydrological process (Hilberts et al, 2004) and as such affect hillslope stability (Talebi et al, 2007). The plan shape defines topographic convergence, which is an important control on subsurface flow concentration.…”