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| Titel |
Characterization of granular flows from the generated seismic signal |
| VerfasserIn |
Maxime Farin, Anne Mangeney, Renaud Toussaint, Julien de Rosny, Phuong-Thu Trinh |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250129817
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| Publikation (Nr.) |
 EGU/EGU2016-9980.pdf |
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| Zusammenfassung |
| Landslides, rock avalanche and debris flows represent a major natural hazard in steep
landscapes. Recent studies showed that the seismic signal generated by these events can
provide quantitative information on their location and amplitude. However, owing to the lack
of visual observations, the dynamics of gravitational events is still not well understood. A
burning challenge is to establish relations between the characteristics of the landslide
(volume, speed, runout distance,...) and that of the emitted seismic signal (maximum
amplitude, seismic energy, frequencies,...).
We present here laboratory experiments of granular columns collapse on an inclined
plane. The seismic signal generated by the collapse is recorded by piezoelectric
accelerometers sensitive in a wide frequency range (1 Hz - 56 kHz). The granular column is
made of steel beads of the same diameter, between 1 mm and 3 mm that are initially
contained in a cylinder. The column collapses when the cylinder is removed. A layer of
steel beads is glued on the surface of the plane to provide basal roughness. For
horizontal granular flows, we show that it is possible to distinguish the phases of
acceleration and deceleration of the flow in the emitted seismic signal. Indeed,
the signal envelope is symmetrical with respect to its maximum, separating the
acceleration from the deceleration. When the slope angle increases, we observe that the
signal envelope looses its symmetry: it stays unchanged during the acceleration
but it is significantly extended during the deceleration. In addition, we propose a
semi-empirical scaling law to describe the increase of the elastic energy radiated by a
granular flow when the slope angle increases. The fit of this law with the seismic data
allows us to retrieve the friction angle of the granular material, which is a crucial
rheological parameter. Finally, we show that the ratio of the radiated elastic energy over
the potential energy lost of granular flows, i.e. their seismic efficiency, increases
when the diameter of the flow grains increases and when the total mass of the flow
decreases. These results explain the dispersion over several orders of magnitude of
the seismic efficiency of landslides observed on the field, ranging from 10−5 to
10−3. |
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