WORKSHOP – LIA D-FRACT -
COURMAYEUR – 2018
PROGRAM & Participants
Monday
Tuesday
Wednesday
09:00
E. Flekkoy
K. J. Maloy
A. Puisto
9:30
M. Ayaz
R. Planet
A. Skaugen
10:00
T. Makinen
T. Vincent Dospital
S. Ben Zev
10:30
Coffee Break
Coffee Break
Coffee break
11:00
V. Vidal
J. Mathiesen
J. Weiss
11:30
M. Moura
G. Linga
M. Korhonen
12:00
SKI / WORK…
WORK / SKI …
SKI / WORK…
16:30
Coffee Break
Coffee Break
17:00
J-C. Géminard
R. Toussaint
17:30
F. Eriksen
V. Levy
18:00
L. Viitanen
F. Dubourg
D. Dysthe
20:00
DINNER
List of Participants
1. S.Santucci Organizer
ENS de Lyon
2. M. Alava Organizer
Aalto
3. J.-C.Géminard
Mechanical stability of disordered media upon deformation
ENS de Lyon
4. V. Vidal
Formation of particle suspensions by gas injection
ENS de Lyon
5. V. Levy
Evolution of the distance between plates in an experimental
granular fault: Implications for earthquake forecast.
ILM Lyon
6. F. Dubourg
Granular Laboratory Quakes: Linking Local and Global
Avalanches
ILM Lyon
7. KJ. Maloy
Pattern formation of frictional fingers in a gravitational
potentia
Oslo, PoreLab
8. E. Flekkoy
Connecting transport and geometry in giant labyrinths
Oslo, PoreLab
9. M. Moura
Burst dynamics in porous media drainage flows
Oslo, PoreLab
10. F. Eriksen
Granular media on drop interfaces:
deformation, patterns & flow driven by electric fields
Oslo, PoreLab
11. M. Ayaz,
On transport and death of film-networks during slow drainage
PoreLab
/Unistra
12. A. Skaugen
Elasticity and plasticity in the phase field crystal model
PGP Oslo
13. R. Toussaint
The art of sinking in saturated soils: the role of fluid on soil
liquefaction during earthquakes, triggering without
pressurization
Unistra,
Strasbourg
14. A. Cochard
Unistra,
Strasbourg
15. T. Vincent Dospital
Thermal effects in the propagation of a crack front
in disordered papers and polymers
Unistra,
Strasbourg
16. S. Ben Zev
The coupling between compaction and pressurization in cyclically
sheared drained granular layers: implications for soil
liquefaction
Unistra,
Strasbourg
17. A. Puisto
Coarsening and mechanics in a mesoscale model of wet foams
Aalto
18. M. Korhonen
Interparticle friction controls submerged granular flows in
simulations
Aalto
19. L. Viitanen,
Static versus Mobile: single intruders in two-dimensional
foams
Aalto
20. T. Mäkinen
Fluctuations in plasticity :
deformation bands in the Portevin–LeChatelier effect
Aalto
21. J. Mathiesen
Flow and stress in porous rock
NBI, Copenhagen
22. G. Linga
Multiphase electrohydrodynamics in complex geometries
NBI, Copenhagen
23. R. Planet
Drainage/imbibition displacements in a gap-modulated Hele-Shaw
cell
UiB, Barcelona
24. J. Weiss
Fracture of disordered quasi-brittle materials and size-effects
on strength from a statistical physics perspective - the case of
concrete
UJF,
25. D. Dysthe
Confined crystal growth instabilities
PGP Oslo
Monday
1. E.G. Flekkøy (PoreLab)
Connecting transport and geometry in giant labyrinths
K. S. Olsen, J. Campbell, B. Sandnes, K.J. Måløy and E.G.
Flekkøy
While the labyrinthine patterns that form during the slow
drainage of a deformable porous medium have been known for a decade
[1], little has been achieved in the way of characterizing these
patterns. While the hydrodynamic forces that generate the
labyrinths are known, the means of describing them has been limited
to measuring their characteristic channel width. Here we start from
the observation that the labyrinths are indeed folded trees and
show how diffusion of random walkers on these structures may serve
as a way of characterizing the geometry.
Branching analysis of a medium sized labyrinth, showing 7
branching orders.
In order to make this connection a Horton-Strahler branching
analysis is carried out, giving rise to a classification of the
pattern in various branching orders. The figure shows these orders
by different colors. If the labyrinth were realized as say, a maze
of hedges, this figure would serve as a map that would show a lost
person the way out. The random walker, which has no map, diffuses
along in a way that is characterized by an anomalous exponent
around 2/3 (normal diffusion being characterized by an exponent of
1). This transport exponent would also characterize the diffusion
of heat if the labyrinth were realized as a structure with thermal
conductivity, or the spreading of a tracer if it were realized as a
substrate for some chemical substance. We predict this exponent
from a simplified model that has the observed branching ratio and
the fractal dimension of the branches. This dimension quantifies
the folding of the branches. Simulations, which produce labyrinths
more than 250 times the size of the experimental ones and therefore
give results of good statistics, confirm the theoretical
prediction.
Reference: [1] Sandnes, B., et al., Labyrinth patterns in
confined granular-fluid systems. Phys. Rev. Lett., 2007. 99(3).
2. Tero Mäkinen (Aalto)
Fluctuations in plasticity: deformation bands in the
Portevin–LeChatelier effect
Some metal alloys exhibit deformation instabilities such as the
Portevin-Le Chatelier effect. The associated strain localizations
and their propagation have been studied experimentally with high
spatiotemporal resolution which allows the study of not only the
propagation velocities but also their fluctuations. This sheds
light on the fluctuations of the underlying dislocation densities.
The results are compared to a minimal one-dimensional model of
plastic deformation in systems with dynamic strain ageing.
3. M. Ayaz (IPG-S / PoreLab)
On transport and death of film-networks during slow
drainage.
M. Ayaz(1,2*) , R. Toussaint(1,2), K. J. Måløy(2) & G.
Schäfer(1) 1 Institut de Physique du Globe de Strasbourg, CNRS /
Université de Strasbourg 2 PoreLab, Physics Department, University
of Oslo
* [email protected]
We study experimentally the residual saturation left behind as a
fully saturated porous media is drained on a quasi two-dimensional
porous model. The model is transparent, allowing the displacement
process and structure to be monitored in space and time.
Observations show the residual saturation to be interconnected by
means of capillary bridges, allowing for seemingly entrapped fluid
to be transported back to the bulk. This process shows dependence
with the Bond number and a statistical decay with increasing
distance from the invasion front. Furthermore, we have analyzed the
spatial connectivity of the networks spanned by capillary
bridges, and examined the occurrence of rupturing of
individual bridges.
4. V. Vidal (ENS de Lyon)
Formation of particle suspensions by gas injection
Particle suspensions are ubiquitous in various domains such as
volcanology (crystal-rich magmas), marine geosciences (gas emission
at the seafloor) or chemical engineering (catalytic reactors). In
most examples, gas rises through a granular bed, then entrains
particles in the above liquid layer. A suspension forms above the
granular bed, resulting from the competition between particle
entrainment by bubbles and sedimentation. We performed experiments
in confined geometry (Hele-Shaw cell) to quantify the properties of
the suspension formed by such process. In particular, we
investigate the influence of the gas flow rate and effective
gravity. The system either reaches a stationary state, or exhibits
a puzzling oscillatory regime - more informations & nice movies
in the talk!
5. Marcel Moura (PoreLab)
Burst dynamics in porous media drainage flows
M. Moura, K.J. Måløy, E.G. Flekkøy and R. Toussaint
We have given experimental grounding for the remarkable
observation made 30 years ago by Furuberg et al. [1] of an unusual
dynamic scaling for the pair correlation function N(r,t) during the
slow drainage of a porous medium. Our experimental setup allows us
to have full access to the spatiotemporal evolution of the
invasion, which was used to directly verify this scaling [2]. We
have connected two important theoretical contributions from the
literature [3,4] to explain the functional dependency of N(r,t) and
the scaling exponent for the short-time regime. A new theoretical
argument was developed to explain the exponent for the long-time
regime.
The intermittent characteristic burst dynamics of the system was
also investigated [5] and we have verified a theoretically
predicted scaling law for the burst size distribution. We have
shown that this system satisfies a set of conditions known to be
true for critical systems, such as intermittent activity with
bursts extending over several time and length scales, self-similar
macroscopic fractal structure and a scaling behavior for the power
spectrum associated with pressure fluctuations during the flow. The
observation of a 1/f scaling region in the power spectra is new for
porous media flows and, for specific boundary conditions, we notice
the occurrence of a transition from 1/f to 1/f2 scaling. An
analytically integrable mathematical framework was employed to
explain this behavior.
Figure 1: Spatiotemporal map showing the evolution of the slow
drainage process in which air displaces a viscous liquid from the
porous network.
References:
[1] L. Furuberg, J. Feder, A. Aharony, and T. Jøssang, Dynamics
of Invasion Percolation, Phys. Rev. Lett. 61, 2117 (1988).
[2] M. Moura, K.J. Måløy, E.G. Flekkøy and R. Toussaint,
Verification of a Dynamic Scaling for the Pair Correlation Function
during the Slow Drainage of a Porous Medium, Phys. Rev. Lett. 119,
154503 (2017).
[3] S. Roux and E. Guyon, Temporal Development of Invasion
Percolation, J. Phys. A 22, 3693 (1989).
[4] S. Maslov, Time Directed Avalanches in Invasion Models,
Phys. Rev. Lett. 74, 562 (1995).
[5] M. Moura, K. J. Måløy, and R. Toussaint, “Critical Behavior
in Porous Media Flow,” EPL (Europhysics Letters) 118, 14004
(2017).
6. J.-C. Géminard (ENS de Lyon)
Mechanical stability of disordered media upon deformation
We first report on a cellular pattern which spontaneously forms
at the surface of a thin layer of a cohesive granular material
submitted to in-plane stretching. We present a simple model in
which the mechanism responsible of the instability is the ''strain
softening'' exhibited by humid granular materials above a typical
strain. Our analysis indicates that such a type of instability
should be observed in any system presenting a negative stress
sensitivity to strain perturbations. We then extend the
experimental study to the case of foam. We shall see that the
mechanisms at play differ significantly.
7. Fredrik K. Eriksen (PoreLab)
Granular media on drop interfaces: Deformation, patterns &
flow driven by electric fields
A. Mikkelsen, K. Khobaib, F. K. Eriksen, K. J. Måløy and Z.
Rozynek
Drops covered by adsorbed particles display a wide range of
research studies and applications, for instance in stabilizing
emulsions or to encapsulate materials. To unlock the enormous
potential of particle-laden drops, it is essential to understand
and control particle organization at drop interfaces and how
surface particles affect drop properties. We utilize electric
fields to experimentally investigate both the mechanics of
particle-covered silicone oil drops suspended in castor oil and the
structuring of particles at drop interfaces. Interestingly, when
subjected to DC electric fields, the deformation magnitude, shape
and electrical properties of drops are altered by changing the
electric field strength, the particle size, conductivity and
particle coverage. Original particle image velocimetry experiments
reveal that electrohydrodynamic (EHD) flows play an essential role
in this regard. In competition with dipolar interactions, EHD flows
also govern the organization of surface particles. This is
especially demonstrated in the final part of this study where we
present an unprecedented method for controlling the local particle
coverage and packing of particles on drop surfaces by simply tuning
the frequency of applied AC electric fields. The approach is
expected to find uses in optical materials and applications.
8. Leevi Viitanen (Aalto)
Static versus Mobile: single intruders in two-dimensional
foams
Foam moving around an obstacle exhibits complex flow behaviour.
In this talk these are examined in two-dimensional channel flow
with two distinct boundary conditions: static and dynamic. The foam
velocity and shear rate fields are experimentally studied along
with spatial distribution of topological rearrangements known as T1
events.
Tuesday
9. Knut Jørgen Måløy (PoreLab)
Pattern formation of frictional fingers in a gravitational
potentia
J. A. Eriksen, E. G. Flekkøy, R. Toussaint, B. Sandnes, O.
Galland and K. J. Måløy
Aligned finger structures, with a characteristic width, emerge
during the slow drainage of a liquid/granular mixture in a
tilted Hele-Shaw cell. A transition from vertical to
horizontal alignment of the finger structures is observed as
the tilting angle and the granular density are varied. The
dynamics is reproduced in simulations. We also show how the system
may explains patterns observed in nature, created during the
early stages of a dyke formation.
10. R. Planet (Barcelona)
Drainage/imbibition displacements in a gap-modulated Hele-Shaw
cell
We consider drainage/imbibition displacements between an
inviscid fluid (air) and a viscous fluid (oil) in a narrow channel
with gap-thickness modulations. We derive the analytical solution
of steady-state front morphologies in imbibition, and compare it to
actual experimental realizations. We also predict the hysteretic
behaviour of the front in the invasion of a single pore (Haines
jumps), and verify it experimentally.
11. T. Vincent-Dospital (IPG-S)
Thermal effects in the propagation of a crack front in
disordered papers and polymers
Tom Vincent-Dospital (1), Renaud Toussaint (1,2), Alain Cochard
(1), Olivier Lengliné (1,2), Stéphane Santucci (3,2), Knut Jørgen
Måløy (4,2)
(1) Institut de Physique du Globe de Strasbourg, CNRS /
Université de Strasbourg, France, (2) Center for Advanced Study,
Academy of Science, Norway, (3) LP ENS, ENS Lyon, France, (4)
Department of Physics, University of Oslo, Norway
During the propagation of a crack in an elastic medium, some of
the system’s energy brought by the external load is reversibly
stored as elastic energy adapting to the crack morphology, while
the rest gets irreversibly dissipated by three main processes: the
creation of new fracture surfaces and defects/dislocations, the
emission of mechanical waves transmitted to the far field and the
Joule heating due to some friction in a damaged zone around the
fracture front. The heat hence generated can in turn have a
significant impact on the physics of the propagation. Notably,
fracture propagation has been shown to be strongly affected by
thermally activated rupture, even when the heterogeneity of the
material properties determines strongly the fracture geometry and
the intermittency of its propagation. This question is notably
central in earth science, where a lot of attention has been
recently set on thermal effects, with the possibility of
thermo-pressurization of faults due the expansion of in situ
fluids. Independently of this pressurization effect, the local rise
of temperature of the zone enduring damage could significantly
affect its creep and the global fracturing process, as understood
by statistical physics and the Arrhenius law.
We are interested in quantifying these different effects with
both experimental set-ups and numerical simulations. We present
three sets of results:
- The first set is based on the infrared and optical imaging of
a crack propagating in a sheet of paper. The temperature field in
the sheet shows local increases of several degrees during the
propagation. We present some numerical simulations that relate the
increase of temperature to the speed at which the crack advances
and the size of the zone around the crack tip in which the heat is
generated.
- The second set is based on the imaging of a fracture in a
heterogeneous interface inside an acrylic glass body. We show that
modeling the crack kinetics based on the material disorder, the
elastic interactions at the crack front, as well as on an Arrhenius
law‚ hence depending on the room temperature ‚ shows good agreement
with all the experimental observations‚ i.e. the scaling laws in
the morphology of the crack front, and the distribution of the
local rupture velocity.
- The third set shows numerical simulations combining both
considerations: the crack propagation is modeled using an Arrhenius
law with a temperature depending on the crack kinetics. We show
that such a model leads to two possible propagation modes: a slow
mode in which the temperature rise at the crack tip has little
effect on the creep and a fast mode in which the crack is thermally
weakened leading to high velocity avalanches. We propose that the
mode at which the crack actually propagates is mainly dependent on
the thermal properties and the toughness heterogeneities of the
medium being fractured.
12. J. Mathiesen (NBI, Copenhagen)
Flow and stress in porous rock
13. G. Linga (NBI, Copenhagen)
Multiphase electrohydrodynamics in complex geometries
14. R. Toussaint (IPG-S / PoreLab)
The art of sinking in saturated soils: the role of fluid on soil
liquefaction during earthquakes, triggering without
pressurization
R. Toussaint1,6*, C. Clément1, E. Aharonov2, M. Stojanova1, S.
Ben Zeev1,2, L. Goren2, G. Sanchez-Colina1,3, E. Altshuler3, A.
Batista-Leyva4, L. Alonso-Llanes3,1 , M. Bousmaha 5 , S. Parez7
*[email protected]
1Institut de Physique du Globe Strasbourg, Strasbourg Cedex,
France,
2Hebrew University of Jerusalem, Jerusalem, Israel
3University of Havana, Havana, Cuba,
4INSTEC, Havana, Cuba
5 University Abdelhamid Ibn Badis of Mostaganem, Algeria
6 PoreLab, University of Oslo, Norway
7 Czech Academy of Science, Prague
Soil liquefaction is a significant natural hazard associated
with earthquakes. Some of its devastating effects include tilting
and sinking of buildings and bridges, and destruction of pipelines.
Conventional geotechnical engineering assumes liquefaction occurs
via elevated pore pressure. This assumption guides construction for
seismically hazardous locations, yet evidence suggests that
liquefaction strikes also under currently unpredicted conditions.
We show, using theory, simulations and experiments, another
mechanism for liquefaction in saturated soils, without high pore
fluid pressure and without special soils, whereby liquefaction is
controlled by buoyancy forces. This new mechanism enlarges the
window of conditions under which liquefaction is predicted to
occur, and may explain previously not understood cases such as
liquefaction in well-compacted soils, under drained conditions,
repeated liquefaction cases, far-field liquefaction and the basics
of sinking in quicksand. We show how this mechanism allows
explaining liquefaction triggering as function of Earthquake
magnitude and epicentral distance. These results may greatly impact
hazard assessment and mitigation in seismically active areas.
References:
· C. Clément, R. Toussaint, M. Stojanova, and E. Aharonov
Sinking during earthquakes: Critical acceleration criteria
control drained soil liquefaction Phys. Rev. E 97, 022905
(2018)
· C Clément, R Toussaint, E Aharanov, Shake and sink:
liquefaction without pressurization, arXiv preprint
arXiv:1802.04391, 2018
· Zeev, S. B., Goren, L., Parez, S., Toussaint, R., Clement, C.,
& Aharonov, E. (2017). The Combined Effect of Buoyancy and
Excess Pore Pressure in Facilitating Soil Liquefaction. In
Poromechanics VI (pp. 107-116).
· Alonso-Llanes, L., Sánchez-Colina, G., Martínez, E.,
Batista-Leyva, A. J., Toussaint, R., & Altshuler, E. (2016).
Intruder Penetration in Granular Matter Studied by Lock-In
Accelerometry. Revista Cubana de Física, 33(2), 95-97.
· Bousmaha, M., Missoum, H., Toussaint, R., & Bendani, K.
(2017, November). Saturated Sandy Soils Mechanical Instability
Under Vibration Effect. In Euro-Mediterranean Conference for
Environmental Integration (pp. 1857-1859). Springer, Cham.
· Sánchez-Colina, G., Alonso-Llanes, L., Martínez, E.,
Batista-Leyva, A. J., Clement, C., Fliedner, C., ... &
Altshuler, E. (2014). Note:“Lock-in accelerometry” to follow sink
dynamics in shaken granular matter. Review of scientific
instruments, 85(12), 126101.
15. Florine Dubourg (ILM)
Granular Laboratory Quakes: Linking Local and Global
Avalanches
F. Dubourg1, S. Lherminier1, R. Planet1,2,3, L. Vanel1, and O.
Ramos1
1 Univ Lyon, Université Claude Bernard Lyon 1, CNRS, Institut
Lumière Matière, F-69622, LYON, France.
2 Departament de FÍsica de la Matèria Condensada, Universitat de
Barcelona, Martí i Franquès 1, E-08028 Barcelona, Spain.
3 Universitat de Barcelona, Institute of Complex Systems, Martí
i Franquès 1, E-08028 Barcelona, Spain.
We present an experimental study aiming to understand the local
origin of the acoustic bursts recorded globally during the shearing
of a two-dimensional granular fault submitted to a constant
pressure. The analysis focuses on their acoustic frequencies.
Experiments with single grains are also performed; they allow
separating the contributions related to collision between
neighbours from shear movements between grains. The results show
that both frictional sliding and collision mechanisms are involved
in the origin of the acoustic bursts. Ultrafast imaging records the
relaxation dynamics related to large acoustic events, identifying
their nature as well-localized processes, instead of a “snow-ball”
avalanche-like scenario. These large events take place along major
force chains, indicating a relationship between the energy
distribution of events and the structure of the force network, and
highlighting the key role of the disorder of the network into a
Gutenberg-Richter-like dynamics.
Typical acoustic signal
16. Victor Levy dit Vehel (ILM)
Evolution of the distance between plates in an experimental
granular fault: Implications for earthquake forecast.
V. Levy dit Vehel1, F. Dubourg1, L. Vanel1, K. J. Måløy2 &
O. Ramos1
1 Univ Lyon, Université Claude Bernard Lyon 1, CNRS, Institut
Lumière Matière, F-69622, LYON, France.
2 PoreLab, Department of Physics, University of Oslo, P. O. Box
1048, 0316 Oslo, Norway.
We have recently developed an experimental system capable of
--for the first time-- reaching a stationary regime following
quantitatively the main laws of seismicity. The intermittent
dynamics of our labquakes consists of frictional failures in the
structure of a compressed granular medium submitted to a continuous
shear. By quantitatively replicating the main laws of seismicity:
Gutenberg-Richter law, Omori law, distribution of waiting times
between events; as well as other qualitative (for the time being)
similarities, our work strongly indicates that these two very
different system: earthquakes and our experiment, are governed by a
similar physics. Moreover, thanks to the possibility of a
significant statistics and better quality measurements than the
real phenomenon, our system corroborates the existence of magnitude
correlation in the dynamics, a result that has been previously
associated to catalogue incompleteness. Here we introduce new
results focusing on the evolution of the packing fraction during
the experiment, particularly around very large quakes and where we
expect a dilatancy of the medium preceding mainshocks. To do that,
we have directly monitored the distance between the plates that
compress the granular fault. Preliminary results indicate a
precursory behaviour that seems more reliable than the analysis
delivered so far by our acoustic data.
Experimental setup
17. Dag Kristian Dysthe (UiO)
Confined crystal growth instabilities
We observe crystals “floating” on a fluid film of 25–50 nm in
thickness due to the disjoining pressure. We find that in this
fluid film there are three end-member nanoconfined growth
behaviors: (1) smooth, (2) a Mullins-Sekerka-like instability
(3) and rough intermittent growth, the latter being faster than the
two former. The intermittent growth rims have regions of load-
bearing contacts that move around the rim causing the crystal to
“wobble” its way upwards. We present strong evidence that the
transition from smooth to rough is a generic confinement-induced
instability that is, until now unexplained.
Wednesday
18. Antti Puisto (Aalto)
Coarsening and mechanics in a mesoscale model of wet foams
Aqueous foams are an important model system that displays
coarsening dynamics. Coarsening in dispersions and foams is well
understood in the dilute and dry limits, where the gas fraction
tends to zero and one, respectively. However, foams are known to
undergo a jamming transition from a fluid-like to a solid-like
state at an intermediate gas fraction, $\phi_c$. Much less is known
about coarsening dynamics in wet foams near jamming, and the link
to mechanical response, if any, remains poorly understood. In this
talk, we discuss coarsening and mechanical response using numerical
simulations of a mesoscale model for wet foams. As in other
coarsening systems we find a steady state scaling regime with an
associated particle size distribution. We relate the time-rate of
evolution of the coarsening process to the wetness of the foam and
identify a characteristic coarsening time that diverges approaching
jamming. In addition, we probe the mechanical response of the
system to strain while undergoing coarsening. We find two competing
time scales, namely the coarsening time and the mechanical
relaxation time. We relate these to the evolution of the elastic
response and the mechanical structure.
19. Skaugen (PGP, Oslo)
Elasticity and plasticity in the phase field crystal model
The phase field crystal model is an efficient phenomenological
model for describing crystal plasticity in the mesoscale without
needing to resolve the fast timescales of lattice vibrations and
phonons. However, this comes at the price of making all dynamics
take place on the same diffusive timescale. In particular, elastic
distortions relax on the same timescale as plastic deformation.
We present some analytical results on the elastic behavior of
the PFC, giving a local expression for the stress tensor. We
analyze kinetics of dislocations as topological defects in
the amplitude expansion, which allows us to relate the motion of
dislocations to the stress. Thus we are able to derive the
Peach-Koehler force under some simplifications.
20. S. BenZeev (IES / IPG-S)
The coupling between compaction and pressurization in cyclically
sheared drained granular layers: implications for soil
liquefaction
BenZeev Shahar 1,4, Goren Liran 2, Parez Stanislav 3, Toussaint
Renaud 4 and
Aharonov Einat 1
[email protected]
1 Institute of Earth Science, Hebrew University of Jerusalem,
Israel;
2 Geological & Environmental Science, Ben-Gurion University
of the Negev, Israel;
3 Institute of Chemical Process Fundamentals of the CAS, Prague,
Czech Republic;
4 Université de Strasbourg, CNRS, Institut de Physique du Globe
de Strasbourg, UMR7516, F-67000 Strasbourg, France;
The dynamics of saturated granular layers during shaking is
controlled by the coupling between grains and fluid. Understanding
such systems is crucial for studies of soil liquefaction,
seismically induced landslides and shear along faults. This study
focuses on the compaction of a near surface well-drained saturated
granular layer during seismic shaking. Compaction is known to
promote soil liquefaction, but the exact feedback mechanism between
compaction and pressurization remains poorly understood. We use
Discrete Element numerical simulations composed of coupled solid
grains and fluid phases under cyclic horizontal shear of the bottom
undrained boundary and a free, completely drained, top layer. We
compare the dynamics under two drainage conditions: First,
simulations of “infinite” drainage, where the fluid pressure is
maintained hydrostatic during the shaking. Second, simulations of
“realistic” drainage in a high permeability layer, whereby fluid
pressure dynamically deviates from hydrostatic values due to local
granular compaction and dilatation. Simulation results show two end
member behaviors, with a transition controlled by the magnitude of
shaking acceleration: At low acceleration the system behaves
rigidly, compaction is negligible and fluid pressure remains
constant even during “realistic” drainage simulations, where it is
allowed to evolve. At high acceleration, significant compaction
occurs in both cases, but the compaction rate is higher in
“realistic” drainage simulations. This rapid compaction trend is
temporally correlated to a transient pore pressure increase that
reaches lithostatic stress values before it drops back to a lower
value. This is an evidence to a feedback mechanism in which
compaction causes pressure increase that can persist under drained
condition as long as the compaction rate is sufficiently high. On
the other hand, this very pressure itself promotes the high
compaction rate. From this we conclude that although well-drained
soils are considered liquefaction-resistant, dynamic coupling
between pore fluid pressure elevation and compaction during seismic
shaking provides a previously unrecognized pathway to
liquefaction.
21. J. Weiss (Univ. Genoble)
Fracture of disordered quasi-brittle materials and size-effects
on strength from a statistical physics perspective - the case of
concrete
22. Marko Korhonen (Aalto)
Interparticle friction controls submerged granular flows in
simulations
Powders, sand and slurries exemplify a class of materials known
as granular media, their constituent particles sharing the
characteristic length scale of 1-1000 micrometers. When subjected
to external stress, these materials can exhibit behavior typical of
both solids and liquids. The latter behavior can be witnessed in
the industrially relevant silo/hopper geometry, where granular
particles flow from a hopper via an orifice under the influence of
gravity, being embedded in either air (dry case) or in water
(submerged case). Performing experiments and CFD-DEM simulations
utilizing this flow geometry, we recovered the Beverloo equation as
expected in the dry case, implying that the outflux of the granular
particles remains constant in such a flow. However, in the
submerged case, a time-dependent, non-monotonic outflux is instead
observed in both experiments and simulations, which can be
explained in the context of an effective shear-thickening
rheology.
30 cm
3 cm
1
2
3
4
b
a
c