Experimental Characterization of the Hydromechanical Properties of the Gypsum Soil of Sebkha of Oran

This paper deals with hydro-mechanical investigation of salinegypsum soil properties from Sebkha of Oran in respect withtheir impact on the feasibility of the project of the second runwayof the Es-Sénia airport in Oran (Algeria). The geologicaland in-situ geotechnical studies prior to the construction phaseof the airport runway revealed underground cavities supposedto be created from salts and gypsum dissolution in the Sebkhasoil. Standard laboratory experiments are used to determinepermeability coefficient, isotherm curve, shear resistance andelastic parameters of two soils. These ones are affected by thevariation of water table level that varies according to the dryperiod (summer) or the rainy period (winter), creating cyclichydric conditions. The paper presents a comparison of parametersof these two soils in saturated and partially saturatedconditions. The results of tests performed in laboratory arecompared with those performed in situ in order to check theirrepresentativeness before a detailed comparison of the effect ofwater conditions. The two soils have similar behavior highlysensible to water with some particularities

Influence du temps sur le comportement du gypse

International audienceThe underground quarry of Grozon gypsum shows instabilities that are a function of the exploitation age. Moreover, the minerals are strongly dissolved in the oldest districts. Concerning the physical properties and instantaneous mechanical behaviour, few differences are to be noted. However the time depended mechanical behaviour from this material is strongly influenced by the hygrometry. The more it is raised, the more deformation rate increase. The acceleration of deformation rate is also for the old working. A Lemaitre like creep law allowed some simulations.La carrière souterraine de gypse située sur la commune de Grozon (Jura) présente de nombreuses instabilités dont l'ampleur est fonction de l'âge d'exploitation des quartiers. Les minéraux constitutifs sont dissous dans les quartiers les plus âgés, illustration du vieillissement du massif rocheux. Les propriétés physiques et mécaniques instantanées sont peu différentes entre les quartiers. Cependant, le comportement mécanique différé est influencé par l'Hygrométrie dans la carrière : plus celle-ci est élevée, plus les vitesses de déformation augmentent. Ces vitesses de déformation sont également plus rapides pour les quartiers les plus anciens. Enfin, une simulation des résultats des essais de fluage a été tentée en utilisant une loi de comportement du type Lemaitre

Temperature and Pressure Dependence of the Effective Thermal Conductivity of Geomaterials: Numerical Investigation by the Immersed Interface Method

The present work aims to study the nonlinear effective thermal conductivity of heterogeneous composite-like geomaterials by using a numerical approach based on the immersed interface method (IIM). This method is particularly efficient at solving the diffusion problem in domains containing inner boundaries in the form of perfect or imperfect interfaces between constituents. In this paper, this numerical procedure is extended in the framework of non linear behavior of constituents and interfaces. The performance of the developed tool is then demonstrated through the studies of temperature- and pressure-dependent effective thermal conductivity of geomaterials with imperfect interfaces

Influence de l'hygrométrie sur le comportement différé du gypse en carrière souterraine

National audienceLe comportement différé des piliers de gypse dans les carrières souterraines peut être influencé par les variations de l'hygrométrie. Cette influence a été étudiée en corrélant des mesures de la convergence de plusieurs galeries et celles de l'hygrométrie dans des conditions d'aérage différentes. Des essais de fluage sous hygrométrie contrôlée, réalisés au laboratoire, ont permis de comprendre et modéliser ce comportement

Investigation on the thermal degradation and kinetic parameters of innovative insulation materials using TGA-MS

Thermogravimetric analyzer coupled to a mass spectrometer (TGA-MS) was used to study the thermochemical behavior of eight samples. Two varieties of straw (wheat and barley) and two others of binder (lime and plaster) have employed to design four composites. These composites can be considered as innovative insulation materials for buildings. The thermal degradation of the different specimens was studied from a temperature of 50 to 1000ºC using increased temperature of 20ºC/min. This thermal degradation is an important element to evaluate the fire behavior and predict the evolution of smoke emitted during an accidental fire for building application. Using MS analyzer, the ion currents evolutions of 16 molecule groups (shared by a m/z ratio) were followed as functions of temperature. TG curves show that the thermal decomposition of composite samples is more complex (3-4 mass loss steps) than the one of the basic materials (1-2 mass loss stages) and seems to be mostly affected by the binder nature. The highest amount of gas in pyrolysis products is associated to m/z=28 ratio and presents more than two thirds of the total quantity. The kinetic parameters were evaluated for the more important mass loss of each sample and their values are in the ranges of 8.29-64.86 kJ/mol, 0.4-3.36 and 1.78 x 10^3 -1.63 x 10^7 min^-1 for respectively the activation energy, the reaction order and the pre-exponential factor.Peer ReviewedPostprint (author's final draft

Pétrofabrique et propriétés mécaniques des argilites

The petrofabric of mudstones influences their thermal, hydraulic and mechanical properties. Measurements of thermal diffusivity, permeability and velocity of ultrasonic waves show that the anisotropy of these properties in this rock is rather low. The diminution of Biot coefficient with axial stress cannot be explained only by the diminution of porosity even by considering an incompressible matrix to 1% for an axial stress varying from 8 to 24 MPa corresponds. The origin of the diminution could be explained by the loss of connection of part of the porous system, hitherto connected, under the effect of an increasing axial stress. An isotropic elastoplastic model is a reasonable approach for the description of the mechanical behaviour of mudstone. However, it is useful to take into account the damage by microfissuring, which could not be neglected and must be considered coupled with plasticity

Estimation of the damage of a porous stone using continuous wave velocity measurements during uniaxial creep tests

International audienc

Etude du comportement à long terme des roches appliquée à l’étude de la stabilité des ouvrages souterrains

Notre étude se propose de combiner une approche expérimentale  à une approche théorique, afin de quantifier l’évolution de la microstructure des roches sous contrainte triaxiale. Le dispositif expérimental permet la mesure continue et simultanée de cinq vitesses d’ondes élastiques différentes sur le même échantillon de roche

Modélisation hydromécanique du comportement des ouvrages souterrains avec un modèle élastoviscoplastique

Le comportement à long terme des excavations souterraines est un enjeu social et économique majeur, en particulier dans le contexte du stockage en formation géologique profonde de déchets nucléaires à Haute Activité et Vie Longue (HAVL). Plusieurs galeries expérimentales ont été creusées dans le laboratoire de recherche souterrain de Meuse/Haute-Marne situé près de Bure en France, où des études sont menées pour comprendre le comportement global de la roche constitutive : l argilite du Callovo-Oxfordien (COx).L objectif de cette thèse est d effectuer une modélisation avec Code_Aster d ouvrages souterrains, et en particulier d une des galeries du laboratoire de Meuse/Haute-Marne, en prenant en compte une approche non locale, l effet du fluage et le couplage hydromécanique dans le cadre de la mécanique des milieux poreux, et de comparer les résultats numériques avec les données expérimentales disponibles.Le modèle élastoviscoplastique spécifiquement utilisé pour cette étude est le modèle L&K : il offre d une part un couplage entre le comportement instantané et différé, et prend en compte d autre part la dilatance, paramètre qui gouverne les déformations volumiques du matériau lors d une sollicitation, et ses fortes variations, caractéristique essentielle des géomatériaux et en particulier du COx. La présence d un fluide s écoulant à travers le matériau va ajouter une composante hydraulique à la modélisation, dont le couplage avec la mécanique est assuré par les équations de Biot. Une autre nouveauté de ce travail concerne le couplage entre ce comportement rhéologique complexe et une approche non locale dans un cadre industriel. Parmi les méthodes de régularisation disponibles dans Code_Aster, la méthode second gradient de dilatation a été choisie parce que bien adaptée aux géomatériaux. Son but est de corriger la dépendance au maillage et les solutions numériques localisées.Une fois les outils numériques opérationnels et les paramètres du modèle L&K calés sur des essais effectués en laboratoire sur des échantillons, un bon accord général a été trouvé entre les résultats numériques et les mesures in situ, sans aucun recalage des paramètres. Les effets du temps observés expérimentalement sur l évolution des déplacements et des pressions d eau sont retrouvés au sein d une même modélisation, validant ainsi la démarche prédictive suivieThe long term behaviour of underground excavations is a social and economic stake, in particular in the context of storage in deep geological formation of high activity and long life nuclear waste. Several experimental galleries have been dug in the underground research laboratory (URL) of Meuse/Haute-Marne located close to Bure in France, where studies are leaded in order to understand the global behaviour of the constitutive rock which is the Callovo-Oxfordian (COx) argillite.The purpose of this PhD Thesis is to establish a modelling with Code_Aster of underground excavations, and especially of a Meuse/Haute-Marne laboratory gallery, taking into account non local approach, creep effect and hydromechanical coupling in the framework of the mechanics of porous media, and then to compare numerical results with available experimental data.The specific elastoviscoplastic model used in this study is the L&K model: it offers a coupling between instantaneous and delayed behaviour, and it takes into account the dilation, parameter which governs the volume strains of the material during a solicitation, and its strong variation, a specificity of geomaterials and so of COx argillite. The fluid flowing through the material adds a hydraulic component to the modelling, which is coupled to mechanic component thanks to Biot s equations.Another novelty of this work concerns the coupling between such complex rheological behaviour and a non local approach in an industrial way. Among methods of regularization available in Code_Aster, the second gradient of dilation is well fitted to geomaterials. Its aim is to correct mesh dependency and numerical localized solutions.After describing numeric tools and setting parameters of the L&K model on laboratory tests, a good general agreement was found between numeric results and in situ measures, without resetting parameters. Time effects experimentally measured on displacement and pore pressure evolution are observed in the same modelling, validating the followed predictive approachNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

<i>In Situ</i> Performance Assessment of a Bio-Sourced Insulation Material from an Inverse Analysis of Measurements on a Demonstrator Building

International audienceThe purpose of this study is to evaluate the potential of bio-sourced material based on cereal straw for an efficient insulation. Decreasing significantly energy consumption of buildings requires not only the very best insulation material for heat loss reduction through the wall but also the reduction of air permeability which can affect automatically the comfort in the building. This is why, propose an insulation material with low thermal conductivity remains insufficient and the evaluation of the performance of the new insulation material in situ in real conditions is an essential step. The experimental building ( PROMETHE demonstrator) is set up with wood frame and multilayered walls composed with cinder blocks and insulation bio-composite based on cereal straw in order to simulate the thermal rehabilitation conditions according the External thermal insulation principle. Each façade is divided in four part with three different insulation bio-composites and naked part for comparison reasons. Hygrothermal sensors are used both inside and outside of the demonstrator, and heat-flux sensor is placed at the cinder blocks biocomposite interface. These in situ measurements are used to compare the efficiency of three bi-sourced materials and for the modeling the hygrothermal behavior of the multilayer wall by using the set of identified parameters in laboratory