Stability of infinite slopes under transient partially saturated seepage conditions

Abstract

[1] Prediction of the location and timing of rainfall-induced shallow landslides is desired by organizations responsible for hazard management and warnings. However, hydrologic and mechanical processes in the vadose zone complicate such predictions. Infiltrating rainfall must typically pass through an unsaturated layer before reaching the irregular and usually discontinuous shallow water table. This process is dynamic and a function of precipitation intensity and duration, the initial moisture conditions and hydrologic properties of the hillside materials, and the geometry, stratigraphy, and vegetation of the hillslope. As a result, pore water pressures, volumetric water content, effective stress, and thus the propensity for landsliding vary over seasonal and shorter time scales. We apply a general framework for assessing the stability of infinite slopes under transient variably saturated conditions. The framework includes profiles of pressure head and volumetric water content combined with a general effective stress for slope stability analysis. The general effective stress, or suction stress, provides a means for rigorous quantification of stress changes due to rainfall and infiltration and thus the analysis of slope stability over the range of volumetric water contents and pressure heads relevant to shallow landslide initiation. We present results using an analytical solution for transient infiltration for a range of soil texture and hydrological properties typical of landslide-prone hillslopes and show the effect of these properties on the timing and depth of slope failure. We follow by analyzing field-monitoring data acquired prior to shallow landslide failure of a hillside near Seattle, Washington, and show that the timing of the slide was predictable using measured pressure head and volumetric water content and show how the approach can be used in a forward manner using a numerical model for transient infiltration.

Analytical solutions for calculating pore-water pressure in an infinite unsaturated slope with different root architectures

“…Nevertheless, the influence of different root architectures ( ( ) g z ) and transpiration rate (T) on PWP distributions have not been fully understood. Although Lu and Godt (2008) and Godt et al (2012) derived analytical solutions for both steady and transient unsaturated seepage for infinite slope without vegetation, these two studies do not consider effects of root water uptake on pore water pressure distributions. As far as the authors are aware, analytical solutions simulating vegetation effects on PWP distributions in sloping ground are not available in the literature.…”

Field and laboratory analysis of the runout characteristics of hillslope debris flows in Switzerland

“…While the initial failure of shallow landslides has been extensively investigated by theoretical approaches, numerical modelling, in-situ monitoring or laboratory experiments (Iverson, 2000;Olivares and Picarelli, 2003;Collins and Znidarcic, 2004;Ng et al, 2008;Klubertanz et al, 2009;Godt et al, 2012;Lehmann and Or, 2012), the transformation of the failure into a flow-like movement is complex with many influencing factors (Iverson et al, 1997). This slide-to-flow phenomena has been treated applying concepts of soil mechanics and a so-called "mobility index approach" (Johnson and Rodine, 1984;Ellen and Fleming, 1987).…”

The Effect of Bedrock Topography on Timing and Location of Landslide Initiation Using the Local Factor of Safety Concept

“…Accordingly, the suction stress and the effective stress, which is the sum of the total stress and the suction stress [24] are reduced. Such a reduction in the effective stress reduces the shear strength of the soil, which may cause failure in the hillslope [12,25]. Therefore, a dynamic assessment of coupled hydromechanical processes in variably saturated hillslope is valuable to assess slope stability.A wide range of studies has focused on developing models to predict the timing and distribution of rainfall-induced landslides [26][27][28].…”