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International audience; In this work, we continue our study of upscaling biofilm processes in porous media from the pore scale to the Darcy scale. We adopt a continuum-level description of biofilms at the pore scale on the basis of work reported in Wood et al. (2002b). We upscale from the pore scale to the Darcy scale using the method ofvolume averaging and we predict the effective dispersion tensor with two- and three-dimensional closure problems. Our results indicate that, for a one-equation local mass equilibrium theory, the primary influence of the biofilm is that the effective diffusion coefficient is smaller than it would be without the presence of biofilm. This effect is important primarily atlow Péclet numbers.

The "Rochers de Valabres" is a fractured rock slope located in the French Alps and afected by rockfall. This slope has been chosen as an experimental site for improving knowledge on mechanisms leading to rockfall. Since 2002 scientific investigations (field observations, monitoring and numerical modelling) have been carried out on the site. A seismic network has recorded a significant seismic activity correlated with existing discontinuities. Mechanical measurements using tiltmeters monitor the slope movements in order to improve the knowledge on thermo-hydromechanical process. Different geometrical and mechanical models have been performed. In 2005 the site was chosen to concentrate research on understanding the efffect of climate change on rock slope stability in the framework of a French national program named STABROCK. This paper presents teh results of field measurements and numerical modelling carried out on the experimental site and the complementary investigations will start within the new research. The aim is to study more accurately the impact of environmental factors on rock slope instability mechanisms and to assess the possible effect of the climate change. Technical results will be integrated in a process of risk management.

International audience; Perennial rivers and streams make a disproportionate contribution to global carbon (C) cycling. However, the contribution of intermittent rivers and ephemeral streams (IRES), which sometimes cease to flow and can dry completely, is largely ignored although they represent over half the global river network. Substantial amounts of terrestrial plant litter (TPL) accumulate in dry riverbeds and, upon rewetting, this material can undergo rapid microbial processing. We present the results of a global research collaboration that collected and analysed TPL from 212 dry riverbeds across major environmental gradients and climate zones. We assessed litter decomposability by quantifying the litter carbon-to-nitrogen ratio and oxygen (O2) consumption in standardized assays and estimated the potential short-term CO2 emissions during rewetting events. Aridity, cover of riparian vegetation, channel width and dry-phase duration explained most variability in the quantity and decomposability of plant litter in IRES. Our estimates indicate that a single pulse of CO2 emission upon litter rewetting contributes up to 10% of the daily CO2 emission from perennial rivers and stream, particularly in temperate climates. This indicates that the contributions of IRES should be included in global C-cycling assessments.

International audience

International audience; Lightly loaded structures constructed on expansive soils may develop structural damage as a result of changes in the soil’s moisture content. This study investigated an analytical model of soil–structure interaction to assess the settlement of dwellings built on swelling soils when droughts occur. The building behavior was investigated with the Euler–Bernoulli beam theory, and the ground behavior was investigated with a Winkler-derived model based on the state surface approach. The analytical model results were compared to those of a finite element analysis using the Barcelona Expansive Model (BExM) performed with Code_Bright. The analytical model was then used to assess the settlement transmission ratio for a typology of clayey soils and different parameters of building. The results indicated that the final deflection of the building increased with the building length and soil suction. The building deflection due to the suction variations was inversely proportional to the load, the rigidity of the building and the embedding depth of the foundation. Increasing these parameters made the building less vulnerable to shrinkage and swelling action.

International audience; The major function of underground nuclear waste disposal is to avoid the migration of radionucleides towards the biosphere during their active period. This function can be deteriorated by the EDZ (excavated damaged zone) around the excavation. The EDZ analysis is therefore crucial in the performance assessment of the storage. The paper deals with the determination of the EDZ around a nuclear waste storage cavity using borehole ultrasonic imaging (azimuthal tomography). Indeed, before processing experimental data obtained with this tool, it is necessary to establish that data can be satisfactorily inverted. This analysis is based on a method that is able to sound and image the rock mass velocity field. The velocity field is numerically simulated (3D geomechanical modeling) based on an assumption on the relationship between stress and velocity fields. In order to evaluate a radial velocity profile starting from inter-sensor distance and their corresponding traveltimes, different ray tracing algorithms are tested using synthetic data. These tests led to a simple and fast approach (implemented in a Mathematica package) to process a large quantity of data.

Despite the scant quantitative data available in the literature, it has been hypothesized that some chemical compounds can have deleterious effects on soil stabilization with lime and cements (e.g., nitrates, phosphates and chlorides). This study intends to assess their influence on soil stabilization quantitatively. An original experimental procedure was followed. Selected soils were mixed with a potential deleterious compound at a concentration representative of what can be found in the field. The performance of the different mixtures in terms of soil stabilization was then assessed by performing mechanical tests on samples submitted to several curing conditions (temperature and humidity). The results showed that the tested compounds are likely to alter the soil stabilization processes and thus lower the mechanical performance of the stabilized soil. The results also showed that it is not possible to determine a single threshold value for the compounds considered because their influence on soil stabilization is also a function of the nature of the soil (silt or fine sand), the type of cement (CEM I or CEM II) and the curing conditions.

International audience; Geological storage of CO2 in unmineable coal seams could be a very interesting option in the sustainable management of coal basins. However, the various chemical and physical parameters that determine the success or failure of this type of operation need to be clarified. The CHARCO project aims at developing methods and analysis techniques in order to define the major parameters enabling optimal CO2 storage conditions. In this framework, 22 coals of different ranks were sampled in different locations and systematically characterized (coal ranks, macerals, porosities, CO2 and CH4 adsorption isotherms ...). The isotherms were modelled using the classical Langmuir formalism in order to obtain their adsorption capacities and their affinity for CO2. The high number of coals and parameters considered in our study allow a statistical treatment using Principal Component Analysis. The sorption capacity can not be easily correlated with any other single parameter. On the other hand, CO2 affinity is correlated with coal rank.

International audience; In this work, we derive two different Darcy-scale models for the transport of biodegradable solutes in porous media containing a microbial biomass that developed under the form of a biofilm. Biofilms are composed of bacterial populations and extra cellular polymeric substances, and grow attached to a solid-fluid interface, e.g. the pore walls of a water-saturated porous medium. We begin with the pore-scale description of mass transport, mass transfer between phases (fluid phase-generally water-and biofilm phase) and biologically-mediated reactions. Then, two limit cases of non-equilibrium transport are identified and characterized. Finally, these processes are upscaled using the method of volume averaging to obtain two different macroscale mass balance models. The models are derived for specific cases of non-equilibrium reactive transport (i.e., spatial concentration gradients may exist in one or both phases), for which mechanisms of mass transfer or reaction kinetics limit the rate of biodegradation. In both cases, a one-equation model can be developed even if non-equilibrium conditions exist. The validity domains of the two considered transport models (the Reaction-Rate Limited Consumption model-RRLC model-and the Mass Transfer Limited Consumption model-MTLC model) are established in terms of reactive and hydrodynamic conditions of transport (Damköhler number and Péclet number). The RRLC model is found to be consistent with direct numerical simulation (DNS) results at high Péclet and Damköhler numbers, while the applicability of the MTLC model is limited to high Damköhler numbers but low Péclet numbers.

International audience; Old tunnels are generally supported by masonry structure. Nowadays, these constructions present many instability problems (cracks, collapses, convergence, etc.) due to aging phenomena on both blocks and mortars. After the analysis of blocks mechanical behaviour over time [Idris, J., Verdel, T., Al-Heib, M., 2008a. Numerical modelling and mechanical behaviour analysis of ancient tunnel masonry structures. Tunnelling and Underground Space Technology 23, 251-263.], we try in this paper to simulate the evolution of masonry joints mechanical behaviour in built tunnels and to quantify the influence of their mechanical proprieties on the tunnel behaviour by the help of the experimental design method and distinct elements numerical modelling

International audience; Many countries are now facing problems related to their past mining activities. One of the greatest problems concerns the potential surface instability. In areas where a room-and-pillar extraction method was used, deterministic methodologies are generally used to assess the hazard of surface collapses. However, those methodologies suffer from not being able to take into account all the uncertainties inherent in any hazard analysis. Through the practical example of the assessment of a single pillar stability in a very simple mining layout, this article introduces a logical framework that can be used to incorporate the different kinds of uncertainties related to data and models, as well as to specific expert's choices in the hazard or risk analysis process. Practical recommendations and efficient tools are also provided to help engineers and experts in their daily work.

In the French model of deep nuclear wastes repositories, the galleries should be backfilled with excavated argillite after the site has been filled. After thousands of years, the degradation of the concrete lining of the galleries will generate an alkaline solute (pH > 12) that would circulate through the backfill. The goal of this paper is to describe the impact of such solute circulation on the properties of compacted argillite. Since additives (bentonite, sand or lime) are often introduced in the remoulded argillite for the backfill, such mixtures were also studied. Saturated-portlandite water was circulated through compacted samples for 3, 6 and 12 months at 60 °C. The shear strength behaviour of the samples was determined with triaxial tests. The microstructure of the samples was analysed via mercury intrusion porosimetry tests and scanning electron microscopy. The results showed that the influence of the alkaline fluid on the properties of the argillite is a function of the nature of the additive. In the case of the calcareous sand, no major changes were observed. The pure argillite underwent a slight decrease in its cohesion due to limited dissolution of its clayey particles. Conversely, intense alteration of the bentonite–argillite mixture was observed, and the shear strength behaviour was modified. Lime addition improved the mechanical characteristics of the argillite.

International audience; The stability of underground mines represents a key issue for active and abandoned mines. Over the last few years, several collapses of underground mines in France have affected existing buildings and infrastructures. Many factors are generally identified as the cause of failures: pillar ageing, fractures, and pillars' height to width ratio, etc. Among the treatment techniques available to prevent instability and reduce the deterioration of pillars, backfill is the most frequently used. A research programme, supported by the French Ministry of the Environment, was developed to study the operability of partial and total backfill using waste material in the Livry-Gargan gypsum mine (near Paris, France), where pillar height is 17 m. The paper focuses on: (1) the characterisation of the gypsum and fill material (laboratory and in situ tests), (2) the in situ measurements, involving 5 pillars equipped with 19 pressure cells, since 1999, (3) and numerical modelling of fractured pillars performed in order to improve understanding of the effects of backfill on the stability of room-and-pillar mines. The study clearly shows the operability and the advantages of partial and total backfill for short-term pillar stability. The induced horizontal pressure generated by backfill can reach 200 kPa. The use of numerical modelling also shows the effect of backfill on fractures and that backfill reduces indicatively the shear displacement and the opening of fractures. Numerical modelling helps in identifying the mechanisms of backfill and in a better understanding of the behaviour of backfilled mines.

International audience; This paper describes a field experiment of stress measurement using the overcoring method performed in a rock slope, called Rochers de Valabres (located in France's Southern Alps Region), a field laboratory site prone to rockfalls. Six measurements were conducted at shallow depths from the surface, moving deeper along a sub-horizontal borehole. The experiment was conducted in heterogeneous and anisotropic gneiss, with the overcored rock elastic properties, as evaluated by biaxial and uniaxial tests, being widely scattered. Since stress calculations are sensitive to all input data uncertainties, strain inversion was, thus, performed using an experimental device and Monte Carlo simulations. The experimental device allows the assessment of rather broad confidence intervals for both stress magnitude and orientation. The results indicate that the stress state in the surface area is quite heterogeneous and may be correlated with topography. The measurements show a nonlinear stress distribution with distance to the free surface, along with high values of principal stresses, despite the vicinity of the surface. Although influenced by local topography, orientations of the principal computed stresses are characterized by a high turnover due to local heterogeneities. The results are roughly in accordance to a 2D finite element model of the site.

The present work is devoted to the determination of the macroscopic poroelastic properties of anisotropic elastic porous materials saturated by a fluid under pressure. It makes use of the theoretical results provided by Withers [Withers, P.J., 1989. The determination of the elastic field of an ellipsoidal inclusion in a transversely isotropic medium, and its relevance to composite materials. Philosophical Magazine A 59 (4), 759–781.] for the problem of an ellipsoidal inclusion embedded in a transversely isotropic elastic medium. The particular case of a spherical inclusion is very important for rock-like composites such as argillite and shales. The implementation of these results in a micromechanical theory of poroelasticity allows to quantify the effects of the solid matrix anisotropy and of pore space on the effective poromechanical properties. Closed form expressions of Biot tensor and of Biot modulus are presented as well as numerical applications for anisotropic shales.

In this present study, the effects of Ethylene-Vinyl-Acetate (EVA) on the conventional characteristics and rheological properties of pure bitumen were investigated. The modified bitumen (PMB) has been prepared in laboratory by mixing bitumen with copolymer EVA. Three different contents of polymer have been tested to evaluate the modification. The basic properties of the PMBs have been determined by using conventional test methods. The results indicated that polymer modification improved the conventional properties of the base bitumen such as; penetrability, softening point and temperature susceptibility. Some observations by UV florescence microscopy have been performed to show the differences in the morphology of the PMBs as a function of polymer content. The rheological behaviour was evaluated with a widely used test that is the complex modulus test in order to reach a model. The results of the investigation indicate that the rheological models can reproduce the effect of polymer modifications with an increase of initial modulus and a decrease of the relaxation time and phase angle with polymer content. Two rheological models such as Huet modified model and Prony series model were used to to characterize the rheological behaviour

International audience; In Lorraine, flooding of the iron mines leads to a degradation of groundwater quality. Based on a global approach, a numerical simulator has been built that can reproduce and predict the evolution of water quality at the overflow point of the mining basin. In order to specify the spatial distribution of these pollutant concentrations, a newmodel has been developed. The basin is represented as a network of homogeneous reservoirs. Although encouraging, the results show the need to specify the spatial organisation of water flow in order to reproduce the pollutant concentrations in the different monitored wells.; En Lorraine, l’ennoyage desmines de fer entraîne une dégradation de la qualité de l’eau souterraine. Basé sur une approche globale, un simulateur numérique a été construit. Il permet de reproduire et de prévoir l’évolution de la qualité de l’eau au point de débordement du bassinminier. Pour tenter de préciser la distribution spatiale de ces concentrations, un nouveau modèle est développé. Le bassin est représenté comme un assemblage de plusieurs réservoirs homogènes connectés entre eux. Bien qu’encourageants, les résultats obtenus démontrent la nécessité de préciser l’organisation spatiale des flux d’eau pour reproduire les concentrations dans les différents puits de contrôle.

International audience; The main objective of the paper is to present a study on compacted expansive soil strains generated by complex hydric or mechanical loadings and their consequences on tested soil compressibility. In the first part of the paper, the suction controlled testing devices are described (osmotic and salt solutions methods). All the presented tests were performed in the range of suctions comprised between 0 and 40 MPa. The consequences of the strains induced by wetting as a function of the applied mechanical stress were analyzed. The results showed that, under these conditions, strain depends on the followed hydraulic path whereas the slope of the plastic compression line λ(s) was only affected by the suction applied during themechanical loading. The second test series demonstrated that the stress path influenced both deformation and slope λ(s) if suction higher than the initial sample suction was imposed during the test. As a conclusion, it could be stated that the slope λ(s) depends on the suction applied during a mechanical loading and on the maximum suction experienced by an expansive material during its past “history”.; L’objectif de cet article est de présenter une étude sur les déformations d’un sol gonflant provoquées par des sollicitations hydriques et/ou mécaniques complexes ainsi que leurs conséquences sur sa compressibilité notamment. Dans la première partie de l’article, les dispositifs expérimentaux à succion contrôlée employés (méthodes osmotique et solutions salines) pour conduire l’ensemble des essais sont décrits brièvement. Les essais ont été réalisés dans la gamme des succions comprises entre 0 et 40 MPa. Les conséquences d’une sollicitation hydrique monotone (humidification) conduite sous différentes contraintes ont d’abord été caractérisées. Il est apparu que dans ces conditions d’essai, les déformations dépendent du chemin de contrainte contrairement à la pente de compression plastique λ(s) qui ne dépend que de la succion imposée durant le chargement mécanique. Une deuxième série d’essais a permis de montrer l’influence du chemin de contrainte sur les déformations ainsique la pente λ(s) si une succion supérieure à la succion initiale des éprouvettes est imposée au cours de l’essai (dessiccation). En conclusion, la valeur de la pente λ(s) dépend de la succion sous laquelle est effectué le chargement mécanique mais aussi de la plus grande succion connue par le matériau au cours de son « histoire ».

International audience; The main purpose of this paper is to examine the impact of a wetting and drying path on the swelling/shrinkage of a compacted lime-treated expansive clayey soil both at the macro- and micro-scales. At the macro-scale, the soil water characteristic curves (SWRCs) of the compacted lime-treated materials (0%, 2% and 5% of lime content) were determined for three curing times (0, 28 and 180 days). The modifications at the micro-scale were assessed with mercury intrusion porosimetry (MIP) tests. The results showed that lime treatment was efficient to prevent the volumetric swelling from the initial state upon wetting. Even if no significant macroscopic volumetric variation was observed, a reorganisation of the microstructure was evidenced. Upon drying, the lime addition led to an alteration of the hydro-mechanical soil behaviour from the initial state by increasing the compacted shrinkage limit suction. However, the volumetric shrinkage of the compacted lime-treated samples remained on the same order of magnitude of the untreated compacted soil, regardless of lime content and curing time. At the micro-scale, the \MIP\ tests showed that drying altered both the macro- and micro-porosity fabric of the lime-treated soils. This study showed that lime treatment had a limited effect on lime-treated compacted soil shrinkage whilst preventing swelling.

International audience; From the beginning of numerical methods, because of several significant improvements, geotechnical engineers no longer need the use of simplifying hypotheses. If theses new techniques for modelling soil structures are attractive. one can fear, because of sophistication, that engineers do not fully understand the code. Then, it seems necessary to establish a system for quality of various basic steps of modelling, and for the coherence of sequence of steps. But, before getting involved in quality system, we consider that a synthesis of actual technological practice would be useful. We propose, herein, various quality notions. We hope this document will emerge on common ward-list in civil engineering modelling.; Depuis que les méthodes numériques existent, des progrès significatifs ont permis de s'affranchir d'un certain nombre d'hypothèses simplificatrices dans le calcul des ouvrages de géotechnique. Les modélisations étant de plus en plus sophistiquées et en l'absence d'un cadre réglementaire, il est apparu nécessaire de s'intéresser à leur qualité. Mais avant de s'engager dans la qualité et l'assurance qualité, une synthèse des pratiques actuelles en matière de terminologie nous a paru utile. Le présent document liste des termes relevant de la qualité en précisant leur interprétation dans le domaine de la modélisation numérique en géotechnique, puis des termes, employés dans le domaine de la modélisation en géotechnique, que l'on peut rattacher au concept de qualité. Pour ces derniers nous avons recensé la définition proposée par les normes relatives à la qualité ou par des dictionnaires, et l'utilisation qui en est faite par différents auteurs. Sur la base de ces informations, nous avons soumis des propositions ou apporté des éléments de réflexion quant à l'utilisation de ces termes. Cette synthèse devrait contribuer à pratiquer un langage commun dans le domaine de la modélisation numérique du moins en géotechnique, et à distinguer les différentes notions relevant de la qualité.

The non-linear mechanical behaviour of two different granites was investigated. Short term triaxial tests have been performed in order to study the short term behaviour (instantaneous growth of cracks) of the rock. A continuous damage model is then proposed. The internal damage variable is directly related to the second order crack density tensor used by Kachanov in the study of effective elastic properties of cracked solids. An instantaneous crack growth criterion has been used to describe the time-independent evolution of the damage tensor. The verification of the model has been performed for various loading paths. The results of a numerical modelling show that it is possible to reproduce most of the observable characteristics of damaged zone around an underground opening excavated into brittle rocks.

International audience; The paper discusses the results of a numerical study which examines the influence of joint constitutive models on the response of a specific jointed rock mass mane up of an anisotropic rock (slate). It presents a comparison between predicted convergences and displacements of rock mass surrounding a pilot gallery, and those measured during field investigations. To perform this analysis, the two-dimensional Distinct Element Method code, UDEC, is used and three joint laws are compared. Based on field investigations for site characterisation, two models are constructed according to fracture density (MODEL A and MODEL B). For each of them, the influence of joint constitutive law on the stability of the gallery is examined, and comparisons between the investigations and predictions are made. Examination of the results shows that there is no noticeable change in stress magnitudes between laws. The displacement magnitudes depend on (1) the constitutive law, (2) the input model parameters and (3) the fracture density. A parametric study in the case of MODEL A indicates that a relatively good march between predicted and measured displacements around the gallery can be observed in certain areas.

International audience; This paper describes a slope slipping in the Sainte-Marie open pit coal mine (South-West of France). The movement and its instrumentation are first described. In a second part we present the model which has been done by the distinct element method, as well as a comparison between the results of field instrumentation and the numerical model. The model fit well the in-situ measurements. Consequently we can now hope to use this kind of model to analyze other parts of the mine which are presently stable but could present similar problems in the future

International audience; In the present study, we investigate the evolution with shear of the viscosity of aqueous suspensions of size-selected natural swelling clay minerals for volume fractions extending from isotropic liquids to weak nematic gels. Such suspensions are strongly shear thinning, a feature that is systematically observed for suspensions of nonspherical particles and that is linked to their orientational properties. We then combined our rheological measurements with small-angle Xray scattering experiments that, after appropriate treatment, provide the orientational field of the particles. Whatever the clay nature, particle size, and volume fraction, this orientational field was shown to depend only on a nondimensional Peclet number (Pe) defined for one isolated particle as the ratio between hydrodynamic energy and Brownian thermal energy. The measured orientational fields were then directly compared to those obtained for infinitely thin disks through a numerical computation of the Fokker-Plank equation. Even in cases where multiple hydrodynamic interactions dominate, qualitative agreement between both orientational fields is observed, especially at high Peclet number. We have then used an effective approach to assess the viscosity of these suspensions through the definition of an effective volume fraction. Using such an approach, we have been able to transform the relationship between viscosity and volume fraction (eta(r) = f(phi)) into a relationship that links viscosity with both flow and volume fraction (eta(r) = f(phi, Pe)).

Sustainable development principles lead earthworks companies to use all natural materials and to reduce the environmental impact of their activities. In this context, the use of industrial organic products derived from the processing of renewable matter has been proposed. In this study, three non traditional products have been selected: an enzymatic solution, a lignosulfonate and an acid solution. In a first approach, hydromechanical properties of four treated soils (a silt, a clayey soil and two sands) were investigated. The experimental results showed interesting applications for the silt when its natural water content is low. Indeed, the compaction ability of the soil was increased after enzymatic and lignosulfonate treatments. Thus, savings of water and energy could be expected during the construction stage. To gain a better understanding of the mechanisms of the treatment products, the microstructure of treated soil were investigated with scanning electron microscopy, mercury injection porosity and was completed by the study of a surfactant addition in soils. The global aim of the study was beyond the characterization of mechanical behavior of treated soils, therefore, environmental balance was also estimated for the different applications defined in accordance to the experimental results. For enzymatic and lignosulfonate treatments, a comparison of the global environmental impact was done thanks to a life cycle assessment methodology. This approach showed that technical and environmental interest are associated for the compaction of dry soils when the production and transport steps have limited environmental impact as demonstrated in the sensitivity analysis, Répondre aux défis du développement durable exige la prise en considération des aspects économiques, sociétaux et environnementaux des projets. Dans le domaine des terrassements, les actions portent notamment sur l'optimisation de la valorisation des matériaux extraits grâce aux techniques de traitement des sols. Le projet s'est principalement porté sur les produits de traitement dérivant de la transformation de matières premières renouvelables : solutions « enzymatiques », lignosulfonates et solutions acides. Des données factuelles concernant les effets des traitements sur les caractéristiques hydromécaniques de quatre sols (un limon, un sol argileux et deux sables) ont été acquises mettant en évidence une augmentation de l'efficacité du compactage après traitement du limon au produit enzymatique et au lignosulfonate. La recherche des mécanismes d'action s'est fondée sur une étude de la microstructure par microscopie électronique à balayage et porosimétrie au mercure complétée par l'évaluation des effets d'un ajout de produits tensioactifs sur les propriétés des sols. L'objectif de l'étude dépasse cependant l'évaluation des modalités d'action des produits et vise également à prendre en compte les préoccupations environnementales. Ainsi, une étude d'analyse du cycle de vie a été menée pour chaque application ce qui a permis d'identifier les conditions optimales pour lesquelles les traitements combinent intérêts techniques et environnementaux. Ces conditions sont réunies lors du compactage des sols secs sous réserve que l'étape de production et de transport des produits ne soit pas excessivement pénalisante comme mis en évidence lors de l'étude de sensibilité

International audience; When subjected to a very high-pH, most of the soil minerals undergo physico-chemical transformation. This could induce strong modifications of the shear strength behaviour of the soil. This issue is of high interest in the framework of the design of deep nuclear wastes repositories, since the degradation of the concrete lining of deep galleries after thousands of years will generate an alkaline solute (pH > 12) that would circulate through the backfill, and alter its hydromechanical characteristics. A study was undertaken to assess the impact of high-pH fluid circulation on the shear strength behaviour of a backfill material. Because of the complexity of the existing constitutive theories, a new approach was used, based on evolutionary polynomial regression (EPR), for modelling of these processes. \EPR\ is an evolutionary data mining technique that generates a transparent and structured representation of the behaviour of a system directly from data. An \EPR\ model was developed and validated using results from a comprehensive set of triaxial tests. Through a sensitivity analysis, the \EPR\ model permitted to identify the specific surface, and to a lesser extent the micropore void ratio, as coupling parameters between hydromechanical behaviour alteration during alkaline fluid circulation and a physical process.

Theextraction of ore and minerals by underground mining may induce groundsubsidence phenomena. These phenomena produce several types of ground movement likehorizontal and vertical displacements, ground curvature and horizontal groundstrain at the surface, and associated building damage in urban regions. Theinfluence function is a well-known and efficient method for the prediction ofthese movements, but its application is restricted to mining configurationswith the same influence angle around the mine. However, this angle may displaydifferent values when the mine is not horizontal or when other subsidenceevents already occurred near the considered mine.In this paper a methodology and analgorithm are developed, based on the traditional influence function method inorder to take into account different influence angles. This methodology isimplemented in the Mathematicasoftware and a case study is presented with data from the Lorraine iron minefield in France. Ground movements calculated with the developed methodologyshow a fair concordance with observed data.

Sustainable development principles lead earthworks companies to use all natural materials and to reduce the environmental impact of their activities. In this context, the use of industrial organic products derived from the processing of renewable matter has been proposed. In this study, three non traditional products have been selected: an enzymatic solution, a lignosulfonate and an acid solution. In a first approach, hydromechanical properties of four treated soils (a silt, a clayey soil and two sands) were investigated. The experimental results showed interesting applications for the silt when its natural water content is low. Indeed, the compaction ability of the soil was increased after enzymatic and lignosulfonate treatments. Thus, savings of water and energy could be expected during the construction stage. To gain a better understanding of the mechanisms of the treatment products, the microstructure of treated soil were investigated with scanning electron microscopy, mercury injection porosity and was completed by the study of a surfactant addition in soils. The global aim of the study was beyond the characterization of mechanical behavior of treated soils, therefore, environmental balance was also estimated for the different applications defined in accordance to the experimental results. For enzymatic and lignosulfonate treatments, a comparison of the global environmental impact was done thanks to a life cycle assessment methodology. This approach showed that technical and environmental interest are associated for the compaction of dry soils when the production and transport steps have limited environmental impact as demonstrated in the sensitivity analysis, Répondre aux défis du développement durable exige la prise en considération des aspects économiques, sociétaux et environnementaux des projets. Dans le domaine des terrassements, les actions portent notamment sur l'optimisation de la valorisation des matériaux extraits grâce aux techniques de traitement des sols. Le projet s'est principalement porté sur les produits de traitement dérivant de la transformation de matières premières renouvelables : solutions « enzymatiques », lignosulfonates et solutions acides. Des données factuelles concernant les effets des traitements sur les caractéristiques hydromécaniques de quatre sols (un limon, un sol argileux et deux sables) ont été acquises mettant en évidence une augmentation de l'efficacité du compactage après traitement du limon au produit enzymatique et au lignosulfonate. La recherche des mécanismes d'action s'est fondée sur une étude de la microstructure par microscopie électronique à balayage et porosimétrie au mercure complétée par l'évaluation des effets d'un ajout de produits tensioactifs sur les propriétés des sols. L'objectif de l'étude dépasse cependant l'évaluation des modalités d'action des produits et vise également à prendre en compte les préoccupations environnementales. Ainsi, une étude d'analyse du cycle de vie a été menée pour chaque application ce qui a permis d'identifier les conditions optimales pour lesquelles les traitements combinent intérêts techniques et environnementaux. Ces conditions sont réunies lors du compactage des sols secs sous réserve que l'étape de production et de transport des produits ne soit pas excessivement pénalisante comme mis en évidence lors de l'étude de sensibilité

While crack propagation is considered as the predominant mechanism of damage in quasi brittle rocks, recent observation on cracking evolution on porous rocks have shown that nucleation of new cracks and back-sliding mechanism of cracks are perhaps as important as the crack propagation. The model proposed here tends to explain the laboratory results that could not be explained within framework of crack-sliding model. A crack nucleation mechanism is then considered to generate an increasing number of cracks based upon a statistical distribution of strain energy cumulated on grain to grain contacts. The increasing role of crack growth and crack coalescence is modeled by an avalanche like mechanism that leads finally to the failure of a porous rock. Predictions of the model are compared with experimentally results in terms of strains and acoustic emission

International audience; This paper deals with the recent research results obtained through SOTREDI research project, “SOil TREatment for DIkes” undertaken by the Lhoist Group, a lime producer, in collaboration with several research centres and universities. Lime-treatment of soils is a process that improves the workability of clayey materials and imparts them strong mechanical properties after compaction. These benefits are well known and are used extensively worldwide for the construction of embankments for roads, highways, railways, industrial platforms… However, little is known about the way lime-treated soils behave in the context of hydraulic structures, where the properties of the materials vs water have to be determined. In a first part of the project, it was demonstrated that lime-treated soils could reach permeability levels equivalent to those of untreated materials (i.e. 10-9 m/s to 10-10 m/s as measured in the laboratory) provided the right moisture content and compaction procedure were used. Full-scale trials showed the feasibility of the procedure at the industrial level. Thanks to the use of modern technology - new mixing plant (stationary or mobile) and kneading compaction - offering a guarantee of homogeneity, adequate textural properties and conditions for placing the materials were obtained. Following this procedure, a real-scale dike was built in September 2011, to validate the applicability of lab results at full scale. In-situ and laboratory (on cored samples) mechanical and hydraulic measurements are in progress on this structure. This experimental embankment is the subject of a first companion paper by M. Froumentin et al. with the Centre d’Expérimentation et de Recherche (CER). In a second part of the project, the effect of the lime-treatment against various failure mechanisms, in particular internal or external erosion, could be highlighted by a series of results: - the shrinkage limit of soils was shifted towards higher moisture contents, well above the optimum moisture content, - the material becomes non-dispersive in the standard Crumb-test, even only 1 day after treatment - the critical shear stress for erosion is increased by one to two orders of magnitude in the Hole Erosion Test and Jet Erosion Test, strongly reducing the risk of piping. Details about these results are described in two other companion papers by S. Bonelli et al. (Irstea) and C. Chevalier et al. (Ifsttar). In parallel, the durability of lime-treatment can be observed after more than 30 years on the Friant-Kern irrigation canal in California, as described in a fourth companion paper by G. Herrier et al. Finally, the data described in this paper strongly suggest that lime-treated soils could be successfully used in the design of earthen hydraulic structures (namely canals, dams, dikes and levees).

National audience; Ground movement hazard is commonly associated with the collapse and the instability of abandoned underground cavities. The related risks can be handled through different strategies, which are made up of measures ranging from urbanization regulatory requirements to technical measures for reducing the hazard or the vulnerability. This paper aims to propose a methodology for evaluating these different strategies according to criteria relevant with sustainable development objectives. It focuses on two levels : identification of criteria on the one hand, and on the other, application in the Moyeuvre-Grande case study through a cost-benefit analysis.; L'aléa " mouvement de terrain d'origine minière " est associé à l'évolution de la stabilité de cavités souterraines abandonnées. La gestion des risques qui en découle peut se faire selon différentes stratégies et conduire à un ensemble de mesures allant de prescriptions réglementaires en matière d'urbanisme à des mesures techniques de réduction de l'aléa ou de la vulnérabilité. L'objectif de cet article est de présenter une méthodologie d'évaluation de ces différentes stratégies selon des critères cohérents avec les objectifs d'un développement durable. Le travail porte d'une part sur l'identification de ces critères et d'autre part sur leur application à l'étude du cas de la commune de Moyeuvre-Grande (57) à travers une analyse coûts-avantages.

The damage of an oolitic limestone during quasi-instantaneous compressive tests and multi-step creep tests was studied using an experimental device which enabled the simultaneous and continuous measurement of strains and elastic wave velocities under mechanical loading and controlled hydrous conditions. The simultaneous measurements of five elastic wave velocities (3 P -waves and 2 S -waves) in different directions of propagation and polarisation allowed us to assess the acoustic tensor at any time during loading and thus continuously monitor the evolution of rock damage. The general trend observed in the experimental results was the strong influence of hydrous conditions on both the quasi-instantaneous and time dependent behaviour of this rock. As traditionally observed in the quasi-instantaneous behaviour of quasi-brittle rocks under deviatoric loading, typical anisotropic straining was observed, confirmed by the anisotropy of the wave velocity measured in axial and lateral directions. However, after full unloading, even if a decrease in all waves’s velocities and dynamic elastic moduli was observed, the quasi-isotropy of waves’s velocities was recovered. This recovery after unloading cycle was observed until stress levels close to the peak (i.e., failure) stress. A comparison of laboratory results with numerical predictions from micromechanical models showed that these observations could not be explained by traditional crack propagation theories and that other mechanisms of crack growth must therefore be considered. These trends were also observed during the loading/unloading stages between each creep step with one notable difference, namely that the anisotropy developed during the creep stage was not recovered during the full unloading. A combination of crack growth and crack nucleation combined with a mechanism of progressive crack sliding and closure seems to explain these unusual results. The nucleation of cracks is mostly related to fast loading while the crack propagation is mostly due to subcritical growth of favourable oriented cracks.

International audience; This paper describes the SOTREDI project, “Soil TREatment for Dikes”, undertaken by Lhoist Group, a lime producer, since 2005. This project was led in partnership with research centres and universities, and presents some potential applications. The objective was to demonstrate that soil treatment with lime, besides enhancing the materials workability, confers high levels of mechanical properties, low permeability values, and is likely to reduce piping and internal erosion hazards, and to significantly increase the erosion resistance against overtopping and overflowing. This paper is a first step toward the application of lime-treated soils in earthen hydraulic structures (namely canals, dams, dikes and levees).

This paper presents the lessons learned from practical application of CO2 storage site monitoring methodology developed to address geochemical aspects of future CO2 storage site. It covers a detailed description of the methodology and tools applied for the extremely complex industrial site that main technical challenge is the presence of the multi sources of CO2 at the surface and in the soil. On the basis of previous research programs conducted on natural CO2 storage sites, a specific geochemical monitoring program was developed that combine both a localized and continuous geochemical monitoring. The paper focuses on the surface gases monitoring techniques spread on specific site to quantify CO2 flux and concentration at different levels from soil-atmosphere-interface : -1m to +1m. The geochemical monitoring was based on the combined use of conventional accumulation chambers and dynamic flow chambers systems equipped with high resolution IR sensors, Fourier Transform infrared sensors equipped with specific gas cell and a CO2 mobile infrared sensor. This first step has lead to the location and discrimination of CO2 sources and the analysis of the carbon cycle involving the influence of anthropogenic events and of the natural seasonal variations. Combined methodology matrix for a geochemical surface survey adapted to CO2storage in Paris basin depth saline aquifer is argued and the measurement results are discussed. C isotopic analyses to insure gas traceability have been also applied. Results are not shown in the paper. On the basis of such combined surface and subsurface gas measurements, seasonal variations of the natural CO2 cycle were identified. As results, sensitivity and variability were considered to suggest the CO2 warning levels adapted to detect CO2 abnormal emissions on the surface. Finally, advanced complementary technologies for both soil and atmospheric gas investigations are also detailled as a part of the survey strategy. For soil gases, a specific completion in a shallow well has been developped to perform the continuous acquisition of CO2 concentrations at a depth of 10 m. For atmospheric gases, a scanning imaging infrared remote sensing system was tested to support atmospheric dynamic survey strategy. This site study applied to Claye-Souilly waste disposal represents the real 'hand on' experience and could be considered as a valuable experience to improve part of the geochemical monitoring program of CO2 storage site.

L'exploitation industrielle des matières premières, parallèlement au développement économique et industriel du 20e siècle, a conduit de nombreux pays occidentaux (France, Allemagne, Belgique, etc.) à exploiter leur sous-sol dans des proportions exceptionnelles. Les mouvements de terrains liés à l'exploitation minière ou à l'effondrement des travaux souterrains abandonnés en région urbaine peuvent induire des dommages aux bâtiments et infrastructures. La détermination de la vulnérabilité des bâtiments en raison de l'affaissement minier dépend du niveau de l'aléa et des caractéristiques des enjeux en surface. Il existe différentes méthodes d'évaluation. L'évaluation des dommages est généralement basée sur des méthodes empiriques existantes et une base de données des bâtiments qui consiste dans les paramètres structuraux et les coordonnées géographiques des bâtiments. Ces méthodes résultent toutes de la combinaison de trois facteurs : typologie, dimensions, résistance au type de phénomène étudié ; intensité du phénomène étudié ; échelle des dégradations. Nous présenterons dans cet article d'abord les méthodes d'évaluation de dommages d'un bâtiment et les avantages et les inconvenants de chaque méthode. L'évaluation de dommages à partir de l'aléa affaissement et la simulation de dommages ont été appliqués à un cas théorique correspondant à une exploitation dans le bassin ferrifère lorrain.

An experimental device was performed for the study of coupling the growth of a Shewanella oneidensis MR-1 bacterial biofilm and the non reactive transport of Brilliant Blue FCF. The biofilm growth was monitored by hydraulic conductivity measurements and by image acquisition with a digital camera. The biofilm volume fraction was estimated through tracer experiments with a macromolecular tracer (i.e., Dextran Blue) as in size-exclusion chromatography or gel filtration chromatography. Then after 29 days of bacterial culture a quasi-homogenous biofilm was grown in the whole flow cell (0,1×0,1×0,05m3) occupying about 50% of void space volume. The influence of biofilm growth on porous media transport properties was evaluated. Conservative tracer experiments with Brilliant Blue FCF run at two hydrodynamic conditions and at two growth steps of biofilm (17 and 29 days) showed the influence of local heterogeneities on transport parameters (i.e., porosity, permeability and hydrodynamic dispersion). Then at 17 days of growth when the biofilm partially covers the porous medium (bottom half of the flow cell) a two-equation model or double-layer model was suitable to characterize the conservative transport. A contrario after 29 days of growth, when the biofilm covers the whole porous medium, a classical fickian model was convenient. Numerical values of longitudinal dispersion coefficient from volume averaging well fitted experimental results, Un dispositif expérimental a été développé pour l'étude du couplage de la croissance d'un biofilm de Shewanella oneidensis MR-1 et du transport conservatif de l'Erioglaucine. La croissance du biofilm a été suivie par mesure de conductivité hydraulique et par acquisition d'images à l'aide d'une caméra digitale. La fraction volumique du biofilm a été caractérisée par des essais d'élution d'une macromolécule (i.e. : le Bleu Dextran) par analogie avec les méthodes de chromatographie d'exclusion ou de filtration sur gel. Ainsi au bout de 29 jours, un biofilm quasi-homogène sur l'ensemble de la cellule d'écoulement (0,1×0,1×0,05m3) et équivalent à 50% du volume poral a été formé. L'influence de la croissance du biofilm sur les propriétés de transport du milieu a été évaluée. Les essais de transport conservatif de l'Erioglaucine effectués pour deux vitesses d'injection et à deux stades de croissance du biofilm (17 et 29 jours) ont montré l'influence d'hétérogénéités locales sur les paramètres de transport (i.e. : la porosité, la perméabilité et la dispersion hydrodynamique). Ainsi après 17 jours de culture quand le biofilm occupe partiellement le milieu poreux (moitié inférieure) un modèle à deux équations ou double milieu permet de caractériser le transport conservatif. A contrario après 29 jours de culture où le biofilm occupe tout le milieu poreux, un comportement fickien classique caractérise le transport. Les valeurs théoriques du coefficient de dispersion longitudinale prédites par la méthode de prise de moyenne volumique ont permis de reproduire de manière satisfaisante le comportement observé expérimentalement

L'exploitation industrielle des matières premières, parallèlement au développement économique et industriel du 20e siècle, a conduit de nombreux pays occidentaux (France, Allemagne, Belgique, etc.) à exploiter leur sous-sol dans des proportions exceptionnelles. Les mouvements de terrains liés à l'exploitation minière ou à l'effondrement des travaux souterrains abandonnés en région urbaine peuvent induire des dommages aux bâtiments et infrastructures. La détermination de la vulnérabilité des bâtiments en raison de l'affaissement minier dépend du niveau de l'aléa et des caractéristiques des enjeux en surface. Il existe différentes méthodes d'évaluation. L'évaluation des dommages est généralement basée sur des méthodes empiriques existantes et une base de données des bâtiments qui consiste dans les paramètres structuraux et les coordonnées géographiques des bâtiments. Ces méthodes résultent toutes de la combinaison de trois facteurs : typologie, dimensions, résistance au type de phénomène étudié ; intensité du phénomène étudié ; échelle des dégradations. Nous présenterons dans cet article d'abord les méthodes d'évaluation de dommages d'un bâtiment et les avantages et les inconvenants de chaque méthode. L'évaluation de dommages à partir de l'aléa affaissement et la simulation de dommages ont été appliqués à un cas théorique correspondant à une exploitation dans le bassin ferrifère lorrain.

International audience; The paper presents the Discrete Fracture Network code RESOBLOK, which couples geometrical block system construction and a quick iterative stability analysis in the same package. The deterministic or stochastic geometry of a fractured rock mass can be represented and interactively displayed in 3D using two different fracture generators: one mainly used for hydraulic purposes and another designed to allow block stability evaluation. RESOBLOK has downstream modules that can quickly compute stability (based on limit equilibrium or energy-based analysis), display geometric information and create links to other discrete software. The advantage of the code is that it couples stochastic geometrical representation and a quick iterative stability analysis to allow risk-analysis with or without reinforcement and, for the worst cases, more accurate analysis using stress-strain analysis computer codes. These different aspects are detailed for embankment and underground works.

International audience; The solid waste decomposition inside a municipal solid waste (MSW) landfill may be enhanced by liquid addition in order to reach landfill stabilization in a reduced period of time as compared to dry-tomb landfills. This liquid addition provides an increased leachate volume and its specific chemical composition leads to fear a degradation of the hydraulic properties of the bottom liner system, especially the mineral part. In this study, the impact of four fluids on the chemical and hydraulic properties of three geosynthetic clay liners (GCLs) currently used in landfill bottom liner systems is evaluated using swelling tests, filter press tests and oedopermeameter tests. Each permeability test is associated to chemical analysis of the fluids before and after contact with the bentonites. The four fluids are two real leachates, a sewage slurry and a leachate from a green waste repository. The three GCLs contain either natural sodium bentonite or sodium-activated calcium bentonite.Filter press results and swell index tests reveal a larger impact on the permittivity of the bentonite of leachates as compared to the other fluids. Oedopermeameter tests lasted one year; they show a variable impact, either negative or positive, of the real leachate on the hydraulic conductivity of the GCLs. Specific conditions, such as pre-hydration, limit the impact of leachate on the hydraulic conductivity. Whatever the method used to determine the permittivity of bentonite or of the GCL, the natural sodium bentonite is less impacted by the fluids than the sodium-activated calcium bentonites.

The study of the precursory signs of a brutal collapse above underground caverns, with an overburden characterized by the presence of a massive and stiff bench, is a major problem for public safety. Thus, to progress in the comprehension and the evolution of the concerned mechanisms, a salt cavern, located in the NE France, was monitored in real-time, since 2004 to 2009, until its collapse. This cavern was mined by solution, until reaching its critical dimension (about 180 m) under a covering of 180 m thick, armed with a stiff Dolomite bench located at 120 m of depth.A multi-parameter high resolution monitoring system aimed at characterizing the precursory signs and following collapse itself. It included both geotechnical and geophysical devices as surface leveling measurements and a permanent microseismic network. This one, which data are the principal subject of this thesis, consisted in nine probes equipped with 40 Hz geophones (5 1D and 4 3D), distributed around and directly below the cavern, including one located in the stiff bench.The evolution of the cavern was marked by two major episodes of microseismic activity:- at the beginning of spring 2008, the dissolution restart in the cavern which caused repeated crisis with several thousand events in a few days, this represent a change in the microseismic regime and marked the cavern instability;- in February 2009, following these observations, the owner decided to trigger the collapse by intensive brine pumping in the cavern. During the three days of the operation, more than 30,000 events were recorded (against 60,000 since 2004).The study of the event signature provides essential information for operational monitoring and the discrimination of these two periods. Particularly, while maximal values reached in amplitude, energy and apparent fundamental frequency are quite stable during the 2008 episodes, the rises of this values are important during the collapse period (prior to the peak of activity), allowed us to suppose its imminence. The evolution of the microseism distribution in terms of energy released and occurrence, calculated similarly to the Gutenberg-Richter law, although often difficult to interpret, has been associated with piezometric level rises, and with small accelerations of surface subsidence. During the collapse, the microseismic activity acceleration follows a power law.Microseisms location required the establishment of an appropriate strategy to ensure the quality and the consistency of the results (record selection, calibration, parametric analysis). However, the use of a constant velocity model over all the period was impossible due to the fast and permanent evolution of the environment. Thus, several models were used, according to the a priori known cavern evolution.The event spatiotemporal distributions, thus located, revealed the existence of preferential failure structures and highlight the role of the stiff bench, located at 120 m depth, L'étude des signes précurseurs d'un effondrement brutal au-dessus de cavités souterraines, dont le recouvrement est caractérisé par la présence d'un banc massif et raide, est un problème majeur pour la sécurité publique. Aussi, pour progresser dans la compréhension et l'évolution des mécanismes mis en jeu, une cavité saline, située dans le NE de la France, a été suivie en temps réel, entre 2004 et 2009, jusqu'à son effondrement. Celle-ci a été exploitée par dissolution, jusqu'à atteindre une dimension critique (de l'ordre de 180 m) sous un recouvrement de 180 m, armé d'un banc raide de Dolomie situé à 120 m de profondeur.Un système de mesures multi-paramètres haute résolution visait à caractériser les signes précurseurs ainsi qu'à suivre l'effondrement lui-même. Il comprenait des dispositifs à la fois géotechniques et géophysiques, dont des mesures de nivellement de surface et un réseau permanent d'écoute microsismique. Ce dernier, dont les données font l'objet principal de cette thèse, était constitué de neuf sondes équipées de géophones 40 Hz (5 unidirectionnels et 4 tridirectionnels), réparties autour et à l'aplomb de la cavité, dont une dans le banc raide.L'évolution de la cavité a été marquée par deux épisodes majeurs d'activité microsismique :- au printemps 2008, la reprise de la dissolution dans la cavité a engendré l'apparition de crises répétées avec plusieurs milliers d'événements en quelques jours, traduisant un changement de régime microsismique, marqueur de l'instabilité de la cavité ;- en février 2009, suite à ces observations, l'exploitant a décidé de provoquer l'effondrement, par le rabattement intensif de saumure dans la cavité. Pendant les trois jours d'opération, plus de 30000 événements ont été enregistrés (sur 60000 depuis 2004).L'étude de la signature des événements apporte des renseignements essentiels pour la surveillance opérationnelle et la discrimination de ces deux périodes. En particulier, alors que les valeurs maximales atteintes en amplitude, énergie au capteur et fréquence fondamentale apparente, sont assez stables au cours des crises, les sauts marqués durant l'effondrement, permettent de présumer de son imminence. L'évolution de la distribution des microséismes en termes d'énergie libérée et d'occurrence, calculée de manière similaire à la loi de Gutenberg-Richter, bien que souvent difficile à interpréter, a pu être associée à des hausses du niveau piézométrique, ainsi qu'à de petites accélérations de l'affaissement mesuré en surface. Pendant la période d'effondrement, le nombre d'événements microsismiques augmente en suivant une loi en puissance.La localisation des microséismes a nécessité la mise en place d'une stratégie adaptée pour garantir la qualité et l'homogénéité des résultats (sélection des enregistrements, calibrage, étude paramétrique).Cependant, l'utilisation d'un modèle de vitesse constant sur toute la période s'est révélé impossible, compte tenu de l'évolution rapide et permanente du milieu. Il a donc été entrepris d'établir des modèles de vitesse différents en fonction des périodes d'évolution de la cavité.Les distributions spatio-temporelles des foyers ainsi localisés montrent l'existence de structures préférentielles de rupture et souligne le rôle majeur du banc raide.Croisées avec les autres mesures acquises sur le site, ces résultats ont permis d'établir un scénario probable d'évolution de la cavité et de proposer quelques recommandations pour la surveillance opérationnelle

The Callovo-Oxfordian claystones properties make them reliable as a geological barrier for the confinement of radioactive wastes. In order to optimally predict their behavior, how they respond to various short and long terms loadings has to be studied. Particularly during the exploitation phase, air is continuously ventilated throughout the galleries. The climatic properties of this air are not balanced with those of the rock, and may perturb its hydromechanical (HM) attributes. Thus, assessing the HM response of the rock under hydric loading seems to be a priority.This dissertation begins with laboratory tests to propose an appropriate physical model. Drying tests were studied as they focus on the HM response of samples undergoing hydric loadings. A first 2D isotropic model is proposed, and then enhanced to 3D by considering a transversely isotropic Young modulus. Secondly, experimental results provide relevant data to estimate poroelastic and transport parameters involved in the model. Estimation is achieved according to an inverse procedure, which minimizes the error between measurements and model predictions. Finally, a real-size test is simulated using 2D models: an isotropic plastic one and a transversely isotropic elastic one.Model predictions reproduce well the laboratory tests data. When simulating the in situ behavior, a rather good agreement is obtained between the numerical and experimental results (although using the parameters estimated at the laboratory scale). However, the model highlights a limited influence of plasticity in the laboratory tests, while dissipative phenomena obviously occur in situ. 3D laboratory simulations do not improve the precision of 2D results, but reproduce more experimental data (mass variations, axial and lateral strains). Moreover, the inversion process is more efficient when ran over various kinds of data. Furthermore, stability of the algorithm is improved when adopting a two-phase convergence (simplex, followed by a gradient-like method). Numerical estimates of the parameters are in agreement with the direct experimental measurements obtained through other tests., Les propriétés des argilites du Callovo-Oxfordien les désignent comme une barrière naturelle sûre pour le stockage de déchets radioactifs. Afin d'optimiser la prédiction de leur comportement, leur réponse à diverses sollicitations à court et long termes est étudiée. Notamment, lors de la phase d'exploitation, l'air ventilé dans les galeries n'est pas à l'équilibre hydrique avec la roche et peut perturber ses propriétés hydromécaniques (HM). Il semble alors essentiel de caractériser la réponse HM de la roche à des sollicitations hydriques.La démarche adoptée consiste à proposer un modèle physique adéquat, sur la base d'essais au laboratoire. L'essai de séchage est retenu puisqu'il permet d'étudier la réponse des échantillons en conditions non-saturées. A partir des résultats HM, un modèle élastique 2D isotrope est proposé, puis est élevé à la 3D avec un module de Young isotrope transverse. Ensuite, les données expérimentales servent à estimer certains paramètres poroélastiques et de transfert du modèle. Cette étape est accomplie par procédure inverse (minimisation de l'erreur mesures-calculs). Enfin, une modélisation 2D du comportement in situ est proposée, et compare les prédictions de modèles plastique isotrope et élastique isotrope transverse.Les simulations d'essais au laboratoire reproduisent assez bien les données expérimentales. Pour la modélisation in situ, une bonne corrélation est obtenue entre les prédictions et les mesures, et ce sans ajustement préalable des paramètres. Toutefois, le modèle souligne une influence limitée de la plasticité à l'échelle du laboratoire, alors que les phénomènes dissipatifs sont marqués in situ. Les modélisations 3D au laboratoire ne donnent pas de résultats plus fins qu'en 2D, mais reproduisent plus de données expérimentales (variations de masse, déformations axiales et latérales). De plus, injecter plusieurs types de données dans la formulation inverse permet d'améliorer la précision de l'algorithme. Par ailleurs, une meilleure stabilité de l'algorithme est obtenue en adoptant une convergence en deux étapes (simplex, puis méthode de type gradient). Les estimations numériques des paramètres corroborent les mesures expérimentales obtenues par ailleurs.

My research is focused on the upscaling of reactive- transport processes in homogeneous and heterogeneous porous media. A particular attention is paid to biological reactions and the impact of biofilms on hydrdynamics behavior of the system., Mes différentes activités de recherche qui s'insèrent dans une problématique axée autour du transport multi-échelle en milieu poreux sont détaillées ici au travers de 3 volets: (1) Influence des hétérogénéités sur les processus de transfert (2) Prise en compte des effets de couplage en transport réactif (3) Impact des processus biologiques sur l'hydrodynamique et le transport Un survol des défis qui restent à surmonter et des perspectives à venir de ce travail de recherche concluent le document.

My research is focused on the upscaling of reactive- transport processes in homogeneous and heterogeneous porous media. A particular attention is paid to biological reactions and the impact of biofilms on hydrdynamics behavior of the system.; Mes différentes activités de recherche qui s'insèrent dans une problématique axée autour du transport multi-échelle en milieu poreux sont détaillées ici au travers de 3 volets: (1) Influence des hétérogénéités sur les processus de transfert (2) Prise en compte des effets de couplage en transport réactif (3) Impact des processus biologiques sur l'hydrodynamique et le transport Un survol des défis qui restent à surmonter et des perspectives à venir de ce travail de recherche concluent le document.

Clayey soils can present large volumetric deformations in response of water content change. This phenomenon of shrinkage and swelling of clayey soils is recognized as a costly natural hazard throughout the world. In France, this cost is reported between 1988 and 2007 to 5 million Euros, ranking in second class of the French natural hazards in terms of cost of damage after the floods. The individual masonry buildings with shallow foundations are the most affected by this phenomenon that causes a differential settlement of the building leading to cracks in facades and structural elements, especially in unreinforced masonry elements. The objective of this thesis was to study the vulnerability of the building, against the shrink-swell hazard through an analysis of soil-structure interaction. This work was focused on three major points: hydro-mechanical behavior of clay soils, soil-structure interaction and evaluation of structural damage. The hydro-mechanical behavior of clay soils was considered by the concept of state surface and integrated into a soil-structure interaction model, based on the Winkler model, with increasingly complex approaches: 1D, 2D and 3D by modeling the building behavior respectively by a spring system, the beam element and the plate element. These models of soil-structure interaction are able to calculate the relative deflection of the building, according to the values of imposed suction, mechanical properties of the structure and hydro-mechanical properties of the soil. The relative deflection of the building is then compared to threshold values of the classical damage categories to assess the building damage. Finally a feasibility study was conducted on the development of vulnerability curves adapted to the problem of shrinkage - swelling of clayey soils. These curves represent the average of structural damage versus suction, for each type of building. These curves were developed based on a classification of expansive soils and a building typology outcome from databases of affected buildings. The average damage is calculated by the Monte-Carlo method, taking into account the variability of the building parameters., Les sols argileux peuvent présenter des variations importantes de volume lors d'un changement hydrique, tel une période de sécheresse. Ce phénomène de retrait-gonflement des sols argileux est à l'origine de nombreux préjudices aux bâtis ce qui le situe, après les inondations, au second rang des aléas naturels français en matière de coût des dommages : 5 milliard d'euros entre 1988 et 2007. Les maisons individuelles sont les plus touchées par ce phénomène qui provoque un tassement différentiel du bâti à l'origine de sa dégradation (fissures dans les éléments de maçonnerie non armée en particulier). L'objectif de cette thèse est d'étudier la vulnérabilité des bâtis vis-à-vis de l'aléa retrait-gonflement à travers une analyse de l'interaction sol-structure. Ce travail s'est porté sur les trois grands volets suivants : le comportement hydromécanique des sols argileux, l'interaction sol-structure et l'évaluation des dommages structuraux. Le comportement hydromécanique des sols argileux a été modélisé par le concept de surface d'état et intégré dans un modèle d'interaction sol-structure inspiré du modèle de Winkler, avec des approches de plus en plus complexes : cas unidimensionnel tout d'abord, 2D ensuite en assimilant la structure à une poutre, puis en 3D en représentant la structure par une plaque. Ces modèles d'interaction sol-structure permettent de calculer la déflexion relative d'un bâti, en fonction d'une valeur de succion imposée et des propriétés mécaniques ou hydromécaniques de la structure et du sol d'assise. La déflexion relative du bâti est alors comparée à des valeurs seuils afin d'évaluer le dommage. La dernière partie de cette thèse consiste en une étude de faisabilité pour le développement de courbes de vulnérabilités adaptées à la problématique du retrait gonflement. Ces courbes représentent la moyenne des dommages d'un type de bâti conçu sur un type de sol gonflant pour une valeur de succion imposée. Ces courbes ont été développées à partir d'une typologie des sols gonflants et d'une typologie des bâtis issue des bases de données des maisons sinistrées. La moyenne des dommages est calculée par la méthode de Monte-Carlo, en prenant en compte la variabilité des paramètres du bâti.

International audience

International audience

International audience; The durability of the mechanical improvements brought by lime once the involved earth structures are exposed to long-term hydraulic conditions (long-term water contact and water circulation) is still under discussion. This paper aims at assessing i) the impact of such hydraulic conditions on the mechanical shear strength of a lime-treated silty soil, and ii) the effect of initial conditions (lime content and compaction conditions) on the lime treatment durability. The results showed that water contact leads to a significant decrease in shear strength. The results also indicated that the mechanical performance of soils exposed to water circulation is highly related to the quantity of water passing through the soil specimens and hence to the permeability of the soils: the lower the permeability, the better the durability. Futhermore, it has been observed that a lime content higher than the lime modification optimum (LMO) enables a better homogeneity of the treatment, giving rise to a longer resistance to water circulation.

International audience; One of the main consequences of the nonassociative character of plastic strains in geomaterials is the existence of failure states strictly inside the Mohr-Coulomb plastic limit surface. This point is first emphasized by considering proportional strain loading paths as generalizations of the classical undrained triaxial path. It is shown that the sign of the second-order work is a proper criterion for analyzing these particular failure states. Then, experimental results and theoretical curves (obtained from an incrementally nonlinear constitutive relation) are compared for the case of proportional stress paths in axisymmetric conditions. Main features of the second-order work criterion are identified, such as the existence of a bifurcation domain together with a number of instability cones inside the Mohr-Coulomb surface. Furthermore, decomposing the second-order work into its isotropic and deviatoric parts makes it possible to compare each of the respective contributions to material instability. Finally, a heuristic boundary value problem is simulated via finite element modelling. A spectral analysis of the symmetric part of the stiffness matrix is conducted to extract the first vanishing eigenvalue and its associated eigenvector. It is found that the displacement field related to this eigenvector appears to be very close to the displacement computed just before global numerical breakdown signalling an effective failure. A plausible explanation is that, considering a material point, the flow rule at the boundary of the bifurcation domain almost coincides with the one describing the failure mechanism on the Mohr-Coulomb plastic limit surface.

In coastal areas, reef-builder worms often are bio-engineers by structuring their physical and biological environment. Many studies showed that this engineering role is determined by the densities of the engineer species itself, the highest densities approximately corresponding to the most stable areas from a sedimentological point of view, and hosting the richest and the most diverse benthic fauna. Here, we tested the potential influence of the spatio-temporal dynamics and the spatial fragmentation of one of the largest European intertidal reefs generated by the marine worm Lanice conchilega (Pallas, 1766) (Annelida, Polychaeta) on the associated benthic macrofauna. We demonstrated that the worm densities do have a significant positive role on the abundance, biomass, species richness and species diversity of the benthic macrofauna and that the reef stability also significantly influences the biomass and species diversity. Moreover, the reef fragmentation has significant negative effects on the abundance, biomass and species richness. In addition to L conchilega densities, the stability and the spatial fragmentation of the reef also significantly structure the associated benthic assemblages. This study demonstrates the interest of "benthoscape ecology" in understanding the role played by marine engineer species from a spatial point of view. (C) 2011 Elsevier Ltd. All rights reserved.