On the capillary stress tensor in wet granular materials

This paper presents a micromechanical study of unsaturated granular media in the pendular regime, based upon numerical experiments using the discrete element method, compared to a microstructural elastoplastic model. Water effects are taken into account by adding capillary menisci at contacts and their consequences in terms of force and water volume are studied. Simulations of triaxial compression tests are used to investigate both macro and micro-effects of a partial saturation. The results provided by the two methods appear to be in good agreement, reproducing the major trends of a partially saturated granular assembly, such as the increase in the shear strength and the hardening with suction. Moreover, a capillary stress tensor is exhibited from capillary forces by using homogenisation techniques. Both macroscopic and microscopic considerations emphasize an induced anisotropy of the capillary stress tensor in relation with the pore fluid distribution inside the material. In so far as the tensorial nature of this fluid fabric implies shear effects on the solid phase associated with suction, a comparison has been made with the standard equivalent pore pressure assumption. It is shown that water effects induce microstrural phenomena that cannot be considered at the macro level, particularly when dealing with material history. Thus, the study points out that unsaturated soil stress definitions should include, besides the macroscopic stresses such as the total stress, the microscopic interparticle stresses such as the ones resulting from capillary forces, in order to interpret more precisely the implications of the pore fluid on the mechanical behaviour of granular materials.Comment: 39 page

Modelling of Cyclic Behavior of Sand in Large Range of Strain Amplitudes

The aim of this paper is to show that it is possible to model the behavior of soils in a large range of strains (10-6 to 10-1), using an elastoplastic law with a unique set of parameters. A multimechanism law with a kinematic hardening was used to model the monotonous and cyclic behavior of sand

Cyclic Loading on Clays

Experimental results using triaxial undrained cyclic tests on remolded and non-remolded are exposed. The influence of the clay structure is shown by choosing four clays with different mineralogies (kaolinite, illite, bentonite, marl). Different over consolidation ratios are used and the fatigue phenomenon is studied in relation to the evolution of the effective stress path

Dynamic Triaxial and Vibratory In-Situ Behavior of Cohesive Soil

In-situ and laboratory shear modulus data are presented and compared. In-situ tests included the cross-hole seismic survey at a stiff marl site, while laboratory tests included the cyclic triaxial test on undisturbed specimens obtained from the same site. The cyclic triaxial device presented in this investigation has been developed and improved so that the reliable response of soil can be measured directly from the specimen over a large range of strain (from 10-6 to 10-2 ). A series of cyclic triaxial tests were performed under stress controlled condition over a range of frequency from 0,5 to 10 Hz on marl samples consolidated anisotropically. Values of shear modulus and damping ration determined for shearing strain amplitude between 10-6 and 10-2 and compared with published results proposed by Seed and Idriss (1970) and Hardin and Drnevich (1972). At low strains, the shear modulus values measured by in-situ and laboratory methods were in a good agreement, but the values from the Hardin-Black\u27s equation were underestimated. The influence of consolidation stress, frequency, and number of load cycles on the shear modulus have also been investigated

Mécanismes de survie de l’élevage ovin sous pressions de l’utilisation territoriale (Cas de la zone Biskra –Eloued)

L’élevage représente 40 pour cent de la valeur mondiale des intrants agricoles et soutiennent les moyens de subsistance et la sécurité alimentaire de près de 1,3 milliard de personnes dans le monde. En l’Algérie, il se considère comme l’identité et l’histoire d’une assez nombreuse population algérienne par le rôle social, économique (avec plus de 12,3% PIB en 2019) et culturel qu’il joue. Par ailleurs, cette tranche de population d’éleveur, parfois marginalisé et zappé entre les oueds et les immenses parcours accentués, étant à la base des risques émergents de divers natures, climatiques, environnementaux , sociaux et territoriaux. L’objectif de ce travail est d’évaluer les différents tensions et pressions territoriales que subissent les systèmes d’élevage dans un berceau localisé au Sud-est de l’Algérie, entre les deux wilayates Biskra et Eloued, bien réputé depuis l’antiquité des jours à ce type de production agricole. Entre temps, de savoir les mécanismes et stratégies majeurs qui sont adoptés au fil des jours par les éleveurs en vue de faire face à ces contraintes multi nature. Une étude transversale à l’aide des enquêtes de type rétrospective de la période étalant de 2018 au 2021 sur un échantillon extrait par commodité de taille 89 fermes d’élevage a été la base des données analysées pour répondre à nos objectifs. Pour certaines données et suite au défaut des informations administratives, soient-elles indisponibles ou ne sont pas à jour ; nous avons utilisé la télédétection pour l’avoir. L’obtenu a évalué une grande menace territoriale qui mettra en suspect la durabilité des systèmes d’élevage et toute entière la population d’éleveur dans la zone étudiée. En addition de la tension du réchauffement climatique par une tendance vers une hyperaridité trop rapide et trop accentuée, s’ajoute une enzootie émergente. Pour faire face à ce genre de souffrance et vivre harmonieusement dans ce territoire, les éleveurs sont obligé de muter leur systèmes de production en diversifiant leurs stratégies alimentaires, leurs gestions des troupeaux et leurs modes de vie par l’art de la mobilisation via motorisation des moyens de leur transport et l’acquisition des outils moderne de multimédia

Measuring the economic relationship between economic ‎growth and industrial production in Algeria During the ‎period ‎ ‎(1970-2014) - testing a hypothesis Kaldor‏ -‏

ارتأينا من هذه الدراسة قياس العلاقة الاقتصادية بين إجمالي الناتج المحلي GDP ومؤشر الإنتاج الصناعي IND في الجزائر خلال الفترة1970-2014 من خلال اختبار فرضية كالدور، بينت نتائج اختبار التكامل المشترك وجود علاقة توازنية طويلة الأجل بين المتغيرتين، وبناءً على نتيجة اختبارات السببية نستنتج وجود علاقة سببية ذات اتجاه واحد من GDP إلى IND في الأجلين القصير والطويل، حيث تساعد التغيرات في الناتج الصناعي والناتج المحلي الإجمالي في تفسير تغيرات الإنتاج الصناعي في الجزائر، تعكس هذه النتائج دور النمو الاقتصادي في تحديد معدل الإنتاج الصناعي.We thought of this study was to measure the economic relationship between the GDP and index of industrial production IND in Algeria during the period 1970-2014 by testing the hypothesis Kaldor, co-integration test results showed the presence of a long-run equilibrium relationship between GDP -IND, and depending on the outcome of causality tests conclude the existence of a one-way from GDP to IND causal relationship in the short and long term, helping to changes in industrial output and GDP in the interpretation of changes in industrial production in Algeria, these results reflect the role of economic growth in determining the rate of industrial production

Modeling the effect of wetting on the mechanical behavior of crushable granular materials

ABSTRACT: It is well known that the compressibility of crushable granular materials increases with the moisture content, due to the decrease of particle strength in a humid environment. An existing approach to take into account the effect of grain breakage in constitutive modeling consists in linking the evolution of the grain size distribution to the plastic work. But how the material humidity can affect this relationship is not clear, and experimental evidence is quite scarce. Based on compression tests on dry and saturated crushable sand recently reported by the present authors, a new non-linear relationship is proposed between the amount of particle breakage and the plastic work. The expression contains two parameters: (1) a material constant dependent on the grain characteristics and (2) a constant depending on the wetting condition (in this study, dry or saturated). A key finding is that the relationship does not depend on the stress path and, for a given wetting condition, only one set of parameters is necessary to reproduce the results of isotropic, oedometric, and triaxial compression tests. The relationship has been introduced into an elastoplastic constitutive model based on the critical state concept with a double yield surface for plastic sliding and compression. The breakage ratio is introduced into the expression of the elastic stiffness, the critical state line and the hardening compression pressure. Incremental stress-strain computations with the model allow the plastic work to be calculated and, therefore, the evolution of particle crushing can be predicted through the proposed non-linear relationship and reintroduced into the constitutive equations. Accurate predictions of the experimental results in terms of both stress-strain relationships and breakage ratio were obtained

Experimental evidence that a high electric field acts as an efficient external parameter during crystalline growth of bulk oxide

International audienceA new crystal growth device, in which a high static external electric voltage (up to 14 kV) is added to a floating zone method, is described. Our first experiments show that the application of such an electric field acts like an external force, introducing a pressure effect which is in direct competition with temperature in the solid/liquid thermodynamic equilibrium. High electric fields could therefore be an additional parameter in crystal growth, opening original routes to the synthesis of new materials

Quasistatic rheology and the origins of strain

Features of rheological laws applied to solid-like granular materials are recalled and confronted to microscopic approaches via discrete numerical simulations. We give examples of model systems with very similar equilibrium stress transport properties -- the much-studied force chains and force distribution -- but qualitatively different strain responses to stress increments. Results on the stability of elastoplastic contact networks lead to the definition of two different rheological regimes, according to whether a macroscopic fragility property (propensity to rearrange under arbitrary small stress increments in the thermodynamic limit) applies. Possible consequences are discussed.Comment: Published in special issue of "Comptes-Rendus Physique" on granular material

Micromechanical analysis of kinematic hardening in natural clay

This paper presents a micromechanical analysis of the macroscopic behaviour of natural clay. A microstructural stress-strain model for clayey material has been developed which considers clay as a collection of clusters. The deformation of a representative volume of the material is generated by mobilizing and compressing all the clusters along their contact planes. Numerical simulations of multistage drained triaxial stress paths on Otaniemi clay have been performed and compared the numerical results to the experimental ones in order to validate the modelling approach. Then, the numerical results obtained at the microscopic level were analysed in order to explain the induced anisotropy observed in the clay behaviour at the macroscopic level. The evolution of the state variables at each contact plane during loading can explain the changes in shape and position in the stress space of the yield surface at the macroscopic level, as well as the rotation of the axes of anisotropy of the material