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| Titel |
Landslides of clayey soils: a dramatic avalanche behavior |
| VerfasserIn |
Asmae Khaldoun, Yves Meheust, Peder Møller, Abdoulaye Fall, Gerard Wegdam, Bert de Leeuw, Jon Fossum, Daniel Bonn |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056424
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| Zusammenfassung |
| Quick clays are unstable soils that can be responsible for severe landslides, like the infamous
Rissa landslide of april 1978 in Norway. Quick clay landslides are usually attributed to
rheology modifications caused by changes in the water content, extraction of the salt by
subsurface water drainage, and/or triggering by external mechanical perturbations.
However, the extreme instability of these soils has until recently remained poorly
understood.
Quick clay is a thixotropic material, in which aging competes with shear rejuvenation. We
study various samples of a natural quick clay from Tiller, near Trondheim (Norway).
Rheometry measurements are done by having the material flow under an imposed constant
shear stress. The bifurcation observed in the rheology as a function of the imposed stress
magnitude provides a precise measurement of the yield stress, and evidences that it strongly
depends on the water content. When the material is resting on a plane slope, the amount of
shear stress that it must sustain is related to the plane inclination; if the inclination is
large enough, the material below a yield surface parallel to the plane is susceptible
to flow. For a sample with a clay content of 61%, the resulting flow is that of a
classic yield stress fluid, however for a clay content of 59% a dramatic avalanche
regime is observed. In the latter "landslide" regime, flow is strongly localized in a
thin lubrication layer on which most of the material slides while undergoing little
deformation. This is typically what was observed during the Rissa landslide: houses and
trees sliding upright down the slope. The landslide regime also results in a much
larger travel distance, and in a final deposit height that is independent of the plane
inclination.
We propose a simple mechanical model that explains the laboratory landslide
observations and allows us to relate them to the mechanical behavior measured in the
rheometer. We also prepare a "synthetic quick clay" with mechanical properties identical to
those of the natural quick clay at all salt concentrations. We show that the presence
of a few percent of swelling clay is crucial, and that there exists a range of salt
concentration for which the material’s elastic modulus is highly dependent on the salt
concentration. This is an evidence of the lansdslide-triggering effect of salt washing by
water.
Reference:
A. Khaldoun et al., Phys. Rev. Lett 103, 188301 (2009) |
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