Liquefaction of immersed granular media under isotropic compression

Abstract

We report an observation of the spontaneous liquefaction of glass beads immersed in water and compacted by external isotropic stress. We show that during compression, loose granular samples exhibit a series of sudden rearrangements accompanied by a transient overpressure of interstitial fluid. Ultimately, spontaneous liquefaction with large deformation of the sample is observed. By contrast, denser samples do not show a liquefaction by maintaining its shape integrity. We then discuss the potential mechanisms which could explain this unexpected liquefaction.

High-temporal-resolution quasideterministic dynamics of granular stick-slip

“…Two phases characterize this sudden change. First, a transient phase ( I 39 ) in which the pore fluid pressure instantaneously rises and fluctuates like an oscillating underdamped system toward a stabilized value within 300 ms; then, a slow dissipation phase ( III 39 ) in which the pore fluid pressure decays slowly toward its steady-state value of . The special intermediate phase II at constant U over a duration larger than one second observed for the specific liquefaction case 39 not observed here.…”

“…In the evolution of the pore pressure (see Fig. 2 c), if the duration of the quasistatic stabilized excess pore pressure exceeds more than one second, catastrophic failure arises, even sometimes for the surprising case of isotropic compression 39 . According to classical granular physics, this isotropic liquefaction should be conceptually impossible.…”

“…S5 ), and the deviatoric stress vanishes. = 1 and = 1 (isotropic stress state) are among the necessary conditions for liquefaction, as the gaps that would result in an extreme case of failure 39 are filled due to very large axial and volumetric deformations.…”

“…In a recent series of careful laboratory experiments using triaxial equipment, we detected, with a high level of confidence, a new spectrum of dynamic instabilities in saturated granular materials. These instabilities include unconventional observed behaviors such as irreversible damage in isotropic compression, termed isotropic collapse, up to the destruction of the granular skeleton, termed isotropic liquefaction 39 , 45 . In this paper, we extend the range of the observed spontaneous behaviors in triaxial compression and discover some new facets of stick-slip phenomena, including some of the largest laboratory earthquakes with the highest observed frictional stress drop to date and even, surprising, rare liquefaction during first stick-slip events under moderate stress loadings.…”

“…We report the rare vanishing frictional stress during the stick-slip phenomenon. The presence of pore fluid in a fully saturated simple two-phase granular assembly is essential in creating the largest laboratory earthquakes, which result in complete destruction of the granular structure 39 .…”