Mechanisms of shallow landslides on soil-mantled hillslopes with permeable and impermeable bedrocks in the Boso Peninsula, Japan

Matsushi, Yuki; Hattanji, Tsuyoshi; Matsukura, Yukinori

doi:10.1016/j.geomorph.2005.10.003

Cited by 87 publications

(48 citation statements)

References 30 publications

(34 reference statements)

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“…In this new environment, shallow landslides contribute ∼ 60 % of the sediment yield of the Waipaoa river during floods and 10 to 20 % of total erosion. Similar conditions occurred in the European Alps until the first half of the 20th century, which led to a considerable increase in erosion rates (Mariotta, 2004). Meusburger and Alewell (2008) reported that, in a catchment in the central Alps, the increase in landslide area by 92 % within 45 years was likely due to dynamic factors like climate and land-use changes and had a decisive influence on landslide patterns observed today.…”

Section: Background and Motivationmentioning

confidence: 78%

“…Data from Lehmann et al (2013) indicate that high pore-water pressures were attained relatively quickly and remained steady across the slope long before failure occurred, and that the decrease in the standard deviation of the water saturation prior to failure indicated an increase in the connectivity of water-saturated regions that reduced soil shear strength across the full length of the slip surface leading to failure. Other data in different localities (e.g., Matsushi et al, 2006;Bordoni et al, 2015) have also shown high, steady pore-water pressure prior to failure. Because our model focuses on the effects of roots and soil strength on slope stability rather than on the details of hydrologic triggering, we choose a simplified, empirical, dual-porosity model for our slope hydrology.…”

Section: Hydrological Triggeringmentioning

confidence: 88%

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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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Section: Background and Motivationmentioning

confidence: 78%

Section: Hydrological Triggeringmentioning

confidence: 88%

Tree-root control of shallow landslides

Cohen

Schwarz

2017

Earth Surf. Dynam.

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“…D'Amato Avanzi et al (2004) recorded slope angles for landslide initiation between 25 • and >45 • with metamorphic sandstone and phyllite as parent material. Slope angles up to 45 • was reported by Shakoor and Smithmyer (2005), with mudrock as parent material, while Matsushi et al (2006) found slope angles between 32 • and 38 • with mudstone and sandstone as parent material. In this study calculated AOR values differed significantly with the presence/absence of basalt benches in the runout path.…”

Section: Discussionmentioning

confidence: 88%

A simple qualitative approach for mapping regional landslide susceptibility in the Faroe Islands

Dahl

Mortensen

Veihe

et al. 2010

Nat. Hazards Earth Syst. Sci.

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Abstract. The Faroe Islands in the North Atlantic Ocean are highly susceptible to landslides. Following recent landslide incidents, Jarðfeingi (Faroese Earth and Energy Directorate) has pointed out, that the risk of human lives or of property being lost or affected by landslides may be increasing. This paper aims at presenting and testing a simple qualitative approach for mapping regional landslide susceptibility in the Faroe Islands, using few key parameters. The susceptibility model holds information about both landslide initiation areas and runout zones. Landslide initiation areas are determined from slope angle thresholds (25 • -40 • ) and soil cover data, while runout zones are delineated using the angle of reach approach taking into account the presence/absence of geological benches in the runout path, which has not been considered in earlier studies. Data input is obtained from a landslide database containing 67 debris flows throughout the Faroe Islands. Angle of reach values differ significantly with the presence/absence of geological benches in the runout path. Two values of angle of reach, 21.5 • and 27.6 • , are used for calculating runout zones. The landslide susceptibility model is tested in a study area at the town of Klaksvík in the northern part of the Faroe Islands. A map validation comparing predicted susceptibility zones with a validation-dataset of 87 actual landslides in the study area reveal that 69% and 92%, respectively, of actual landslide initiation areas and runout zones are correctly predicted. Moreover 87% of the actual landslides are included in the overall predicted landslide susceptibility areas.Correspondence to: M.-P. J. Dahl (mpjd@ruc.dk)

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“…is related to the widely used 'flow-net' method (Stephens, 1985), based on a linear interpolation between the hydraulic head values measured in the adjacent tensiometers, as often used in subsurface soil water monitoring (e.g. Anderson and Burt, 1978;Matsushi et al, 2006). In this study ordinary kriging was implemented to construct the equipotential lines (Goovaerts, 1997), using a zonal anisotropic variogram model (Pannatier, 1996).…”

Section: Field Monitoringmentioning

confidence: 99%

“…The combined contributions of subsurface flow exfiltrating at the surface and those contributions from direct rainfall onto the saturated portions are termed 'saturation excess runoff' (Dunne and Black, 1970), in contrast to the infiltration driven runoff, named 'infiltration excess runoff' (Horton, 1933). However, the process of saturation excess runoff is mostly related to wetlands and riparian zones (Dunne et al, 1975;Coates, 1990;Wilson et al, 1991), as well as to shallow soils (Matsushi et al, 2006;Retter et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

The influence of a compacted plow sole on saturation excess runoff

Verbist

Cornelis

Schiettecatte

et al. 2007

Soil and Tillage Research

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Subsoil compaction due to conventional tillage techniques and its relation to subsurface flow and runoff was investigated on a sloped field. The presence of a plow sole was confirmed by significantly higher penetration resistances between 20 and 40 cm depth, a significantly higher soil bulk density and a 14% decrease in drainage pore space compared to the top layer. Ring infiltrometer measurements also confirmed a significant reduction of the saturated hydraulic conductivity at 30 cm depth, indicating a limited permeability. With the use of an extensive grid of tensiometers, matric heads were monitored and the occurrence of a temporary water table on top of the plow sole was confirmed in a number of cases. Equipotential lines in the top saturated layer indicated the occurrence of subsurface flow parallel to the slope surface in a downward direction. For the whole measuring period, when a perched water table was observed, 91% of the rainfall events caused runoff and this number increased with increasing rainfall intensity. For low and medium rainfall intensities (<10 mm h À1 ), 66% and 63% of the runoff events were related to saturation of the top soil. Therefore, it was concluded that over a period of 20 months saturation excess runoff as a result of subsoil compaction was an important contributor to surface runoff and soil loss. #

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Mechanisms of shallow landslides on soil-mantled hillslopes with permeable and impermeable bedrocks in the Boso Peninsula, Japan

Cited by 87 publications

References 30 publications

Tree-root control of shallow landslides

Tree-root control of shallow landslides

A simple qualitative approach for mapping regional landslide susceptibility in the Faroe Islands

The influence of a compacted plow sole on saturation excess runoff

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