“…Counterintuitively, the most destructive stick-slip, in terms of irreversible damage of the granular structure, is not caused by the most powerful event in terms of mechanical energy. After the first stick-slip, less than one-tenth of the failure stress is enough to completely destroy the granular structure in a rare diffuse liquefaction failure 59 .…”
Section: Analysis and Discussionmentioning
confidence: 99%
“…Experimentally, these large dynamic instabilities may appear under some specific conditions: (1) an initially structural anisotropic state created by the moist tamping fabrication technique and revealed by a high anisotropic coefficient during isotropic drained compression 59 , (2) an initially loose threshold solid fraction at 20 kPa of confining stress with random loose packing, and (3) an axial strain rate below the critical axial strain rate (critical velocity in 6 , 72 ) during triaxial drained compression 17 .…”
Section: Analysis and Discussionmentioning
confidence: 99%
“…Counterintuitively, the most destructive stick-slip, in terms of irreversible damage of the granular structure, is not caused by the most powerful event in terms of mechanical energy. After the first stick-slip, less than one-tenth of the failure stress q f is enough to completely destroy the granular structure in a rare diffuse liquefaction failure 59 . Probability density distributions of deviatoric stress drop q normalized by q f for various constant confining stresses p 0 , from 50 up to 500 kPa, following the simple power-law of 3/2 (triangle).…”
We report high-temporal-resolution observations of the spontaneous instability of model granular materials under isotropic and triaxial compression in fully drained conditions during laboratory tests representative of earthquakes. Unlike in natural granular materials, in the model granular materials, during the first stage of the tests, i.e., isotropic compression, a series of local collapses of various amplitudes occurs under random triggering cell pressures. During the second stage, i.e., shearing under triaxial compression, the model granular samples exhibit very large quasiperiodic stick-slip motions at random deviatoric triggering stresses. These motions are responsible for very large stress drops that are described by power laws and are accurate over more than 3 decades in logarithmic space. Then, we identify the quasideterministic nature of these stick-slip events, assuming that they are fully controlled by the cell pressure and solid fraction. Finally, we discuss the potential mechanisms that could explain these intriguing behaviors and the possible links with natural earthquakes.
“…Counterintuitively, the most destructive stick-slip, in terms of irreversible damage of the granular structure, is not caused by the most powerful event in terms of mechanical energy. After the first stick-slip, less than one-tenth of the failure stress is enough to completely destroy the granular structure in a rare diffuse liquefaction failure 59 .…”
Section: Analysis and Discussionmentioning
confidence: 99%
“…Experimentally, these large dynamic instabilities may appear under some specific conditions: (1) an initially structural anisotropic state created by the moist tamping fabrication technique and revealed by a high anisotropic coefficient during isotropic drained compression 59 , (2) an initially loose threshold solid fraction at 20 kPa of confining stress with random loose packing, and (3) an axial strain rate below the critical axial strain rate (critical velocity in 6 , 72 ) during triaxial drained compression 17 .…”
Section: Analysis and Discussionmentioning
confidence: 99%
“…Counterintuitively, the most destructive stick-slip, in terms of irreversible damage of the granular structure, is not caused by the most powerful event in terms of mechanical energy. After the first stick-slip, less than one-tenth of the failure stress q f is enough to completely destroy the granular structure in a rare diffuse liquefaction failure 59 . Probability density distributions of deviatoric stress drop q normalized by q f for various constant confining stresses p 0 , from 50 up to 500 kPa, following the simple power-law of 3/2 (triangle).…”
We report high-temporal-resolution observations of the spontaneous instability of model granular materials under isotropic and triaxial compression in fully drained conditions during laboratory tests representative of earthquakes. Unlike in natural granular materials, in the model granular materials, during the first stage of the tests, i.e., isotropic compression, a series of local collapses of various amplitudes occurs under random triggering cell pressures. During the second stage, i.e., shearing under triaxial compression, the model granular samples exhibit very large quasiperiodic stick-slip motions at random deviatoric triggering stresses. These motions are responsible for very large stress drops that are described by power laws and are accurate over more than 3 decades in logarithmic space. Then, we identify the quasideterministic nature of these stick-slip events, assuming that they are fully controlled by the cell pressure and solid fraction. Finally, we discuss the potential mechanisms that could explain these intriguing behaviors and the possible links with natural earthquakes.
“…2 , in logarithmic scale to emphasize the suddenness in behavioral changes in the millisecond scale (details in Supplementary Materials S1 ). Remind that the cell pressure remains constant within 0.1 kPa during the whole instability motion without any visible macroscopic shear stress 17 . The final approaches an asymptotic value of 0.615, which is still far below the maximum packing fraction (0.639) for an assembly of spherical particles 20 .…”
Section: Resultsmentioning
confidence: 99%
“…One complementary non-contact portable laser vibrometer and one free-field prepolarized microphone measure the local lateral surface vibration and the radial sound pressure outside the triaxial chamber. Two LVDT sensors record the sample axial and volumetric changes, and , to estimate the global axial strain , the global volumetric strain and the global solid fraction (the volume of solids to the total volume) during the isotropic loading (details in 16 , 17 ). Figure 2 Typical temporal evolution of isotropic collapse (blue) and liquefaction (red) on 0.7 mm CVP beads in isotropic drained compression: successively vertical top cap acceleration, normalised excess pore pressure, permanent incremental axial and volumetric strain.…”
Unexpectedly, granular materials can fail, the structure even destroyed, spontaneously in simple isotropic compression with stick-slip-like frictional behaviour. This extreme behaviour is conceptually impossible for saturated two-phase assembly in classical granular physics. Furthermore, the triggering mechanisms of these laboratory events remain mysterious, as in natural earthquakes. Here, we report a new interpretation of these failures in under-explored isotropic compression using the time-frequency analysis of Cauchy continuous wavelet transform of acoustic emissions and multiphysics numerical simulations. Wavelet transformation techniques can give insights into the temporal evolution of the state of granular materials en route to failure and offer a plausible explanation of the distinctive hearing sound of the stick-slip phenomenon. We also extend the traditional statistical seismic Gutenberg–Richter power-law behaviour for hypothetical biggest earthquakes based on the mechanisms of stick-slip frictional instability, using very large artificial isotropic labquakes and the ultimate unpredictable liquefaction failure.
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