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| Titel |
Rheological behaviour of Trièves clay, and applications to landslide dynamics |
| VerfasserIn |
Guénolé Mainsant, Guillaume Chambon, Denis Jongmans, Laurent Baillet, Eric Larose, Grégory Bièvre |
| 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 |
250051480
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| Zusammenfassung |
| Clayey landslides are common worldwide. In the Trièves area (south of Grenoble, French
Alps), which is mainly covered by a thick Quaternary clay layer, several landslides with
different dynamics are continuouly monitored (L’Harmalière landslide, Avignonet landslide,
etc.). The velocity of these slides can vary dramatically (from cm/y to m/s), with earthslides
evolving to earthflows, depending on the meteorological conditions (rainfall, snowmelt),
water infiltration in the mass, slope and geometry of the substratum. These factors may
change the stress state applied to the sliding mass and define its evolution with time.
However, in such a dynamic context, the geotechnical properties of the material,
such as Atterberg limits, are not sufficient to define the behavior of clay slides.
Knowledge of the full rheological behaviour of the clay, ie of the relationships between
stresses, strains, and strain rates, is required. To that purpose, we performed laboratory
rheometric parallel-plate tests on samples of Trièves clay (taken from a gully close to
L’Harmalière landslide) with different water contents and different times of rest (after a
preshear).
Trièves clay was identified as a viscoplastic material with a highly pronounced viscosity
bifurcation. Below a yield stress Ïc, the material behaves as a solid. Above the
yield stress, on the contrary, the material abruptly starts flowing, with a relatively
high critical shear rate (Ëγc = 1 - 2.10-1s-1). The value of the yield stress Ïc
strongly depends on the gravimetric water content (GWC) of the material: 160Pa for
GWC = 68%, 210Pa for GWC = 62%, 400Pa for GWC = 55%. The yield
stress also varies with the time of rest. On the contrary, the value of the critical
shear rate γËc appears essentially independent of these parameters. Trièves clay also
displays a clear thixotropic behaviour: above the yield stress, the fluidization of
the material may be delayed by several tens of seconds after the application of
stress, indicating that the destructuration of the material does not only depend on
the mechanical solicitation but also on the time during which this solicitation is
applied.All these rheological properties could potentially play a key role in the
slide-to-flow transition observed in the Trièves lanslides, explaining how dramatic
and sudden fluidization can occur, and highlighting the influence of time on this
process. |
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