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| Titel |
Acoustic emission rate stress sensitivity caused by stress perturbations during brittle creep deformation of Fontainebleau sandstone |
| VerfasserIn |
Torbjorn Bjork, Alexandre Schubnel, Karen Mair, Sergio Vinciguerra |
| 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 |
250055353
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| Zusammenfassung |
| Three tri-axial compression experiments were performed on 7% porosity Fontainebleau
sandstone cores, at 30MPa confining pressure and 10MPa pore pressure. During
each tests, stress, strain, elastic wave velocities and acoustic emissions (AE) were
recorded.
The first experiment was performed at a constant strain rate of 10-5s-1 and brittle
failure occurred at 440MPa shear stress. The AE rate increased up to failure. AE
hypocenters delineate the fracture plane. Post failure AE rate follows Omori law with an
exponent close to 1. Post failure damage is also located mainly along the fracture
plane.
The second experiment was performed in creep, with constant shear stress stages
at 400, 410, 415, 420 and 435MPa. The constant shear stress stages lasted from
two days (for the lowest ones) to one hour for the last one. During this last stage,
macroscopic failure occurred. AE hypocenters locations show that strain localisation was
initiated early in the experiment, even before the first constant shear stress stage.
Damage accumulated within a nucleation zone from which macroscopic failure was
initiated.
The third experiment was also performed in creep, with the same constant shear
stress staged loading as in the second experiment. However, in this case, small
sinusoidal stress oscillations of 100s period were superimposed to the axial load and
confining pressure (+/- 0.1MPa for the confining pressure and +/- 0.5MPa for the
shear stress, both oscillations being anti-correlated). The acoustic emission rate
closely followed the oscillations, both in primary, secondary and tertiary secondary
creep.
These results suggest, that at least in intact porous rocks, small stress perturbations can
well perturb the background micro-seismicity rate. |
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