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| Titel |
Granular Shear Zone Formation: Acoustic Emission Measurements and Fiber-bundle Models |
| VerfasserIn |
Gernot Michlmayr, Dani Or |
| 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 |
250078029
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| Zusammenfassung |
| We couple the acoustic emissions method with conceptual models of granular material
behavior for investigation of granular shear zone formation and to assess eminence of
landslide hazard. When granular materials are mechanically loaded or sheared, they tend to
produce discrete events of force network restructuring, and frictional interaction at grain
contacts. Such abrupt perturbations within the granular lattice release part of the elastic
energy stored in the strained material. Elastic waves generated by such events can be
measured as acoustic emissions (AE) and may be used as surrogates for intermittent
structural transitions associated with shear zone formation. To experimentally investigate the
connection between granular shearing and acoustic signals we performed an array of
strain-controlled shear-frame tests using glass beads. AE were measured with two different
systems operating at two frequency ranges. High temporal resolution measurements of the
shear stresses revealed the presence of small fluctuations typically associated with
low-frequency (< 20 kHz) acoustic bursts. Shear stress jumps and linked acoustic signals
give account of discrete events of grain network rearrangements and obey characteristic
exponential frequency-size distributions. We found that statistical features of force jumps
and AE events depend on mechanical boundary conditions and evolve during the
straining process. Activity characteristics of high-frequency (> 30 kHz) AE events is
linked to friction between grains. To interpret failure associated AE signals, we
adapted a conceptual fiber-bundle model (FBM) that describes some of the salient
statistical features of failure and associated energy production. Using FBMs for
the abrupt mechanical response of the granular medium and an associated grain
and force chain AE generation model provides us with a full description of the
mechanical-acoustical granular shearing process. Highly resolved AE may serve as a
diagnostic tool not only for detection of shear zone development and straining in granular
matter and but also for investigating internal grain scale mechanical processes.
The AE method could be integrated into monitoring networks of landslide-prone
slopes and other early warning systems for abrupt mass release (snow avalanches). |
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