Editorial: Hydromechanical Instabilities in Geomaterials: Advances in Numerical Modeling and Experimental Techniques (original) (raw)
Related papers
IRN GeoMech workshop on hydromechanical instabilities. Booklet of abstracts
2023
Dear all, It is our pleasure to welcome you in Aix-en-Provence for this international workshop co-organized by the international research network GeoMech and the research department AQUA of INRAE. Granular materials are involved in many natural hazards, such as landslides, avalanches, dike or dam failures, etc. Due to their discrete nature, they have a complex mechanical behavior resulting from local interactions between grains and collective behaviors organized at different scales. Thus, the failure modes of geomaterials can take several forms: diffuse failure possibly resulting in liquefaction, localized failure with shear bands at several scales (from a few grains to the size of the complete system), mixed mode failure, etc. Moreover, granular materials being porous, they are very often subjected to water infiltration likely to induce important changes of microstructure that can affect their physical, hydraulic and mechanical properties. The main objective of this workshop is to review recent advances in the understanding of the elementary mechanisms of destabilization of granular materials and their impact on failure modes (e.g. liquefaction, strain localization). The topics addressed during the workshop may be related, for instance, to the mechanical response and stability of geomaterials in the presence of capillary or solid bridges (sintering, biocalcification, dissolution/precipitation, ...), internal erosion (suffusion and clogging), surface erosion, etc. We hope that the list of forthcoming talks will lead to fruitful discussion and possibly to future collaborations.
Diffuse instabilities with transition to localization in loose granular materials
International Journal for Numerical and Analytical Methods in Geomechanics, 2012
This paper is concerned with diffuse and other ensuing failure modes in geomaterials when tested under homogeneous states of shearing in various loading programs and drainage conditions. Material instability is indeed the basic property that accounts for the instability of an initially homogeneous deformation field leading to diffuse failure and strain localization in geomaterials. The former is normally characterized by a runaway type of failure accompanied with a sudden and violent collapse of the material in the absence of any localization phenomena. Against this backdrop, we present a brief overview of material instability in elastoplastic solids where one finds a rich source of theoretical concepts including bifurcation, strain localization, diffuse failure and second-order work, as well as a considerable body of experiments. Some compelling laboratory experimental studies of material instability with focus to diffuse failure are then presented and interpreted based on the second-order work. Finally, various material instability analyses using an elastoplastic constitutive and a general finite element analysis of the above-mentioned laboratory experimental tests are presented as a boundary value problem. It is shown that instability can be captured from otherwise uniform stress, density and hydraulic states, whereas uniform deviatoric loads are being applied on the external boundaries of a specimen. Although the numerical simulations reproduce well the laboratory experimental results, they also highlight the hierarchy of failure modes where localization phenomena emerge in the post-bifurcation regime as a result of a degradation of homogeneity starting from a diffuse mode signalled by a zero second-order work.
A Multi-scale Framework for Modeling Instabilities in Fluid-Infiltrated Porous Solids
Many natural and man-made materials, such as sand, rock, concrete and bone, are multi-constituent, fluid-infiltrated porous solids. The failure of such materials is important for various engineering applications, such as CO2 sequestration, energy storage and retrieval and aquifer management as well as many other geotechnical engineering problems aimed to prevent catastrophic failures due to pore pressure build-up. This dissertation investigates two mechanical aspects of fluid infiltrated porous media, i.e., the predictions of diffuse and localized failures of porous media and the heterogeneous microstructures developed after failures. We define failures as material conditions in which homogeneous deformation becomes unattainable. To detect instabilities, a critical state plasticity model for sand is implemented. By seeking bifurcation points of the incremental, linearized constitutive responses, we establish local criteria that detect onsets of drained soil collapse, static liquefaction and formation of deformation bands under locally drained and undrained conditions. Fully undrained and drained triaxial compression simulations are conducted and the stability of the numerical specimens are assessed via a perturbation method. To characterize deformation modes after failures, a multi-scale framework is designed to determine microstructural attributes from pore space extracted from X-ray tomographic images and improve the accuracy and speed of a multi-scale lattice Boltzmann/finite element hierarchical flow simulation algorithm. By comparing the microstructural attributes and macroscopic permeabilities inside and outside a compaction band formed in Aztec Sandstone, our numerical study reveals that elimination of connected pore space and increased tortuosity are the main causes that compaction bands are flow barriers.
Quasi-static versus dynamic failure instabilities in fluid-saturated porous media
Comptes Rendus Mécanique, 2002
Using a linear perturbation approach, we show that under quasi-static conditions, unbounded growth of perturbations coincides with localization under drained or undrained conditions. Under dynamic loadings, unbounded growth is related either to the emergence of stationary discontinuities (and these are set by drained conditions) or to the appearance of the flutter phenomenon (acceleration waves). For associative behaviour the inception of unbounded growth is always set (under both static and dynamic conditions) by the singularity of the drained acoustic tensor. It is only for non-associative flow that unbounded growth may correspond to undrained localization in quasi-static conditions and to flutter under dynamic conditions. To cite this article: A. Benallal, C. Comi, C. R. Mecanique 330 (2002) 339-345. 2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS porous media / plasticity / perturbation / localization / static / dynamic Modes de rupture sous conditions quasi-statiques et dynamiques dans les milieux poreux saturés Résumé
Instabilities development in partially molten rocks
Partially molten rocks (PMR) are characterized by specific and contrasting behaviours. For instance, large-scale and smaller scale structures are consistently oriented in a migmatitic body with those of the surroundings, indicating that the migmatites were deformed as a whole. By contrast, ubiquitous strain partitioning and melt dis-TERMINI CHIAVE: reologia, materiali bifasici, migmatiti.
Morphological instabilities of stressed solids
Le Journal de Physique IV, 1998
When a solid is submitted to constant and homogeneous applied stresses, sinusoidal instabilities are supposed to develop by diffusion on its surface. When sources of non-homogeneous stresses like defects are present in its bulk, localized instabilities seem to be more adapted to describe its surface evolution.
Triggering of instabilities in materials and geosystems
2009
Materials from the laboratory to geological scales respond to perturbations in a complex nonlinear fashion. In particular, the response to finite perturbations which cause failure (triggering) is an important, yet poorly understood, issue. Causes of failure may either be exogenous (precipitations, pore pressure, seismic waves, or in the materials context, mechanical perturbations) or endogenous (chemomechanical deterioration, creep deformation, microcracking and microplasticity).
Material Instabilities in Solids
1989
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Tectonophysics, 2016
We study pinch-and-swell structures in order to uncover the onset of strain localization and the change of deformation mechanisms in layered ductile rocks. To this end, boudinaged monomineralic veins embedded in an ultramylonitic matrix are analyzed quantitatively. The swells are built up by relatively undeformed original calcite grains, showing twinning and minor subgrain rotation recrystallization (SGR). Combined with progressive formation of high-angle misorientations between grains, indicative of SGR, severe grain size reduction defines the transition to the pinches. Accordingly, dynamically recrystallized grains have a strong crystallographic preferred orientation (CPO). Towards the necks, further grain size reduction, increasingly random misorientations, nucleation of new grains and a loss of the CPO occur. We postulate that this microstructure marks the transition from dislocation to diffusion creep induced by strain localization. We confirm that the development of boudins is insensitive to original grain sizes and single-crystal orientations. In order to test these microstructural interpretations, a self-consistent numerical grain size evolution is implemented, based on thermo-mechanical principles, end-member flow laws and microphysical processes. Applying constant velocity and isothermal boundary conditions to a 3-layer finite element pure shear box, pinch-and-swell structures emerge out of the homogeneous layer through grain size softening at a critical state. Viscosity weakening due to elevated strain rates and dissipated heat from grain size reduction promotes strain rate weakening until a critical grain size is reached. At this point, a switch from dislocation to diffusion creep occurs. This state locks in at local steady states and is microstructurally expressed in pinches and swells, respectively. Thus, boudinage is
Bifurcations in granular media: macro- and micro-mechanics approaches
Comptes Rendus Mécanique, 2007
Various failure modes related to different kinds of bifurcations occur in nonassociated elastoplastic materials such as geomaterials. After presenting experimental evidence, we study this question by means of phenomenological constitutive relations and direct numerical simulations based on the discrete element method. The second-order work criterion related to diffuse failure modes is particularly considered within the framework of continuum and discrete mechanics. The equations of the bifurcation domain boundary and unstable stress direction cones are established. Diffuse failure is simulated numerically by perturbing bifurcation states. To cite this article: F. Darve et al., C. R. Mecanique 335 (2007).