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| Titel |
Developing an Experimental Simulation Method for Rock Avalanches: Fragmentation Behavior of Brittle Analogue Material |
| VerfasserIn |
Øystein Thordén Haug, Matthias Rosenau, Karen Leever, Onno Oncken  |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076894
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| Zusammenfassung |
| Gravitational mass movement on earth and other planets show a scale dependent
behavior, of which the physics is not fully understood. In particular, the runout
distance for small to medium sized landslides (volume < 106m3) can be predicted
by a simple Coulomb friction law consistent with a constant kinetic coefficient
of friction at the landslide base. This implies that the runout can be considered
independent of volume. Large volume landslides (rock avalanches), however, show a
dependence of runout on volume. This break in scaling behavior suggests that different
dynamics control small and large landslides/rock avalanches. Several mechanisms have
been proposed to explain this scale dependent behavior, but no consensus has been
reached.
Experimental simulations of rock avalanches usually involve transport of loose granular
material down a chute. Though such granular avalanche models provide important insights
into avalanche dynamics, they imply that the material fully disintegrate instantaneously.
Observations from nature, however, suggests that a transition from solid to “liquid” occurs
over some finite distance downhill, critically controlling the mobility and energy budget of
the avalanche. Few experimental studies simulated more realistically the material
failing during sliding and those were realized in a labscale centrifuge, where the
range of volumes/scales is limited. To develop a new modeling technique to study
the scale dependent runout behavior of rock avalanches, we designed, tested and
verified several brittle materials allowing fragmentation to occur under normal gravity
conditions.
According to the model similarity theory, the analogue material must behave dynamically
similar to the rocks in natural rock avalanches. Ideally, the material should therefore deform
in a brittle manner with limited elastic and ductile strains up to a certain critical
stress, beyond which the material breaks and deforms irreversibly. According to
scaling relations derived from dimensional analysis and for a model-to-prototype
length ratio of 1/1000, the appropriate yield strength for an analogue material is in
the order of 10 kPa, friction coefficient around 0.8 and stiffness in the order of
MPa.
We used different sand (garnet, quartz) in combination with different matrix materials (sugar,
salt, starch, plaster) to cement it. The deformation behavior and strength of the samples was
tested using triaxial compression tests at atmospheric confining pressures. Proper material
properties were obtained using well-sorted, well-rounded, medium grained quartz
sand with gypsum plaster as matrix. The favored analogue material is produced by
thoroughly mixing the quartz sand with gypsum and water. Afterwards, sufficient
time is given to allow cementation by the gypsum. The material typically exhibits
elastic deformation up to 0.3% strain and additionally |
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