A multidimensional stability model for predicting shallow landslide size and shape across landscapes

Milledge, David; Bellugi, D. G.; McKean, J. A.; Densmore, Alexander L.; Dietrich, W. E.

doi:10.1002/2014jf003135

Cited by 114 publications

(151 citation statements)

References 73 publications

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“…Figure 6 shows that when the topsoil stratum is thin it can remain stable even for very low values of effective cohesion, whereas, thicker soils tend to require a much higher effective cohesion for stability. This result is in keeping with other physically based modelling studies of the relationships between the geometry of slopes, strata and shallow landslides in cohesion controlled slopes (Frattini and Crosta, 2013;Milledge et al, 2014). Ignoring the effects of water table location and pore water pressures, the greater self-weight of soil at the base of a thicker soil stratum generates higher shear stresses and requires greater shear resistance for stability than in a shallower soil.…”

Section: Preparatory and Triggering Factors Driving Slope Instabilitysupporting

confidence: 69%

Dealing with deep uncertainties in landslide modelling for disaster risk reduction under climate change

Almeida

Holcombe

Pianosi

et al. 2017

Nat. Hazards Earth Syst. Sci.

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Abstract. Landslides have large negative economic and societal impacts, including loss of life and damage to infrastructure. Slope stability assessment is a vital tool for landslide risk management, but high levels of uncertainty often challenge its usefulness. Uncertainties are associated with the numerical model used to assess slope stability and its parameters, with the data characterizing the geometric, geotechnic and hydrologic properties of the slope, and with hazard triggers (e.g. rainfall). Uncertainties associated with many of these factors are also likely to be exacerbated further by future climatic and socio-economic changes, such as increased urbanization and resultant land use change. In this study, we illustrate how numerical models can be used to explore the uncertain factors that influence potential future landslide hazard using a bottom-up strategy. Specifically, we link the Combined Hydrology And Stability Model (CHASM) with sensitivity analysis and Classification And Regression Trees (CART) to identify critical thresholds in slope properties and climatic (rainfall) drivers that lead to slope failure. We apply our approach to a slope in the Caribbean, an area that is naturally susceptible to landslides due to a combination of high rainfall rates, steep slopes, and highly weathered residual soils. For this particular slope, we find that uncertainties regarding some slope properties (namely thickness and effective cohesion of topsoil) are as important as the uncertainties related to future rainfall conditions. Furthermore, we show that 89 % of the expected behaviour of the studied slope can be characterized based on only two variables -the ratio of topsoil thickness to cohesion and the ratio of rainfall intensity to duration.

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Section: Preparatory and Triggering Factors Driving Slope Instabilitysupporting

confidence: 69%

Dealing with deep uncertainties in landslide modelling for disaster risk reduction under climate change

Almeida

Holcombe

Pianosi

et al. 2017

Nat. Hazards Earth Syst. Sci.

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“…In compression, following the work of Schwarz et al (2015) we assume that the soil compressional resistance is mobilized across the shear plane that forms during the failure of a downslope wedge, similar to the earth pressure force in the geotechnical engineering literature that develops during the passive state when a retaining wall moves downslope toward the adjacent backfill (e.g., Milledge et al, 2014). According to Schwarz et al (2015), the mobilized force on the downslope wedge scales with the maximum passive earth pressure force F p and with the displacement, i.e.,…”

Section: Bond Forces Due To Soilmentioning

confidence: 99%

“…In the large majority of cases, slope stability models add apparent cohesion to the soil to simulate root reinforcement (e.g., Milledge et al, 2014;Bellugi et al, 2015;Hwang et al, 2015). Few models include the effects of root distribution heterogeneity (Stokes et al, 2014), and none consider the stress-strain behavior of root reinforcement and the strength of roots in compression.…”

Section: Introductionmentioning

confidence: 99%

Tree-root control of shallow landslides

Cohen

Schwarz

2017

Earth Surf. Dynam.

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Abstract. Tree roots have long been recognized to increase slope stability by reinforcing the strength of soils. Slope stability models usually include the effects of roots by adding an apparent cohesion to the soil to simulate root strength. No model includes the combined effects of root distribution heterogeneity, stress-strain behavior of root reinforcement, or root strength in compression. Recent field observations, however, indicate that shallow landslide triggering mechanisms are characterized by differential deformation that indicates localized activation of zones in tension, compression, and shear in the soil. Here we describe a new model for slope stability that specifically considers these effects. The model is a strain-step discrete element model that reproduces the selforganized redistribution of forces on a slope during rainfall-triggered shallow landslides. We use a conceptual sigmoidal-shaped hillslope with a clearing in its center to explore the effects of tree size, spacing, weak zones, maximum root-size diameter, and different root strength configurations. Simulation results indicate that tree roots can stabilize slopes that would otherwise fail without them and, in general, higher root density with higher root reinforcement results in a more stable slope. The variation in root stiffness with diameter can, in some cases, invert this relationship. Root tension provides more resistance to failure than root compression but roots with both tension and compression offer the best resistance to failure. Lateral (slope-parallel) tension can be important in cases when the magnitude of this force is comparable to the slope-perpendicular tensile force. In this case, lateral forces can bring to failure tree-covered areas with high root reinforcement. Slope failure occurs when downslope soil compression reaches the soil maximum strength. When this occurs depends on the amount of root tension upslope in both the slope-perpendicular and slope-parallel directions. Roots in tension can prevent failure by reducing soil compressive forces downslope. When root reinforcement is limited, a crack parallel to the slope forms near the top of the hillslope. Simulations with roots that fail across this crack always resulted in a landslide. Slopes that did not form a crack could either fail or remain stable, depending on root reinforcement. Tree spacing is important for the location of weak zones but tree location on the slope (with respect to where a crack opens) is as important. Finally, for the specific cases tested here, intermediate-sized roots (5 to 20 mm in diameter) appear to contribute most to root reinforcement. Our results show more complex behaviors than can be obtained with the traditional slope-uniform, apparent-cohesion approach. A full understanding of the mechanisms of shallow landslide triggering requires a complete re-evaluation of this traditional approach that cannot predict where and how forces are mobilized and distributed in roots and soils, and how these control shallow landslides shape, size, loc...

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“…Fiber reinforcement provided by tree roots increases riverbank shear strength (Abernethy and Rutherfurd, 2001). Even when this root reinforcement has limited depth penetration, increased friction along the edges of a potential slide mass can control the size of individual failure events (e.g., slump blocks) (Milledge et al, 2014;Wang et al, 2016): the greater the root reinforcement, the larger the individual failure events. By extension, deforestation will tend to decrease the size of individual failure events, but the reduced shear strength of riverbank materials will tend to increase their frequency.…”

Section: Resultsmentioning

confidence: 99%

Modification of river meandering by tropical deforestation

Horton

Constantine

Hales

et al. 2017

Geology

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Tropical forests are the only forest biome to have experienced increased rates of forest loss during the past decade because of global demands for food and biofuels. The implications of such extensive forest clearing on the dynamics of tropical river systems remain relatively unknown, despite significant progress in our understanding of the role of trees in riverbank stability. Here, we document rates of deforestation and corresponding average annual rates of riverbank erosion along the freely meandering Kinabatangan River in Sabah, Malaysia, from Landsat satellite imagery spanning A.D. 1989-2014. We estimate that deforestation removed over half of the river's floodplain forest and up to 30% of its riparian cover, which increased rates of riverbank erosion by >23% within our study reaches. Further, the correlation between the magnitude of planform curvature and rates of riverbank erosion only became strongly positive and significant following deforestation, suggesting an important role of forests in the evolution of meandering rivers, even when riverbank heights exceed the depth of root penetration.

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A multidimensional stability model for predicting shallow landslide size and shape across landscapes

Cited by 114 publications

References 73 publications

Dealing with deep uncertainties in landslide modelling for disaster risk reduction under climate change

Dealing with deep uncertainties in landslide modelling for disaster risk reduction under climate change

Tree-root control of shallow landslides

Modification of river meandering by tropical deforestation

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