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This paper proposes a new interface constitutive model for fully grouted rock-bolts and cable-bolts based on pull-out test results. A database was created combining published experimental data with in-house tests. By means of a comprehensive framework, a Coulomb-type failure criterion accounting for friction mobilization was defined. During the elastic phase, in which the interface joint is not yet created, the proposed model provides zero radial displacement, and once the interface joint is created, interface dilatancy is modeled using a non-associated plastic potential inspired from the behavior of rock joints. The results predicted by the proposed model are in good agreement with experimental results. The model has been implemented in a finite element method (FEM) code and numerical simulations have been performed at the elementary and the structural scales. The results obtained provide confidence in the ability of the new model to assist in the design and optimization of bolting patterns.

For a good management and precise tracks of hydrogen quantities stored in salt caverns, this paper presents a study on hydrogen transport in rock salt during cycling. It provides a novel mathematical–numerical model that couples the cavern thermodynamics with the transport mechanisms of hydrogen in the saturated rock salt in a fully coupled thermo–hydraulic framework. Both the two–phase Darcian percolation and the Fickian diffusion are used to account for hydrogen migration in the interstitial brine of the rock salt. Due to the absence of experimental data, a parametric study is furnished. The effect of cycling within the cavern on the migration mechanisms is discussed in detail. Simulations have confirmed the dependency of the Darcian percolation on the model parameters. However, for similar applications, this dependency might be limited. The value of the Fickian diffusion coefficient affects indirectly the Darcian percolation. The two–phase percolation becomes more of a piston–like for very small values of the diffusion coefficient. On a real–scale typical cavern, and over a period of 40 years, simulations have proven that the quantity of hydrogen lost into the surrounding rock salt is unimportant. Besides, cycling renders this quantity more insignificant.

Power-to-Gas–Oxyfuel, or Electrolysis-Methanation-Oxyfuel, is an advanced concept that addresses some concerns of conventional Power-to-Gas: supply of high-purity CO 2 , release of greenhouse gases to the atmosphere and fate of the O 2 from electrolysis. Due to the intermittent nature of several renewable energy sources, massive storage is needed to balance supply and demand. This paper focuses on the storage phase required for Electrolysis-Methanation-Oxyfuel. Synthetic CH 4 , O 2 and CO 2 have to be stored at different times. Due to the high fluid rates and volumes required, salt caverns are potential candidates. While salt caverns have been used for decades to store CH 4 , storage of CO 2 and O 2 has not been implemented to date. A generic seasonal scenario with a 200 MW oxyfuel unit is investigated. Numerical modelling that couples cavern thermodynamics with the thermomechanical response of the surrounding rock salt has been performed. The results, although exploratory, show that the caverns would be stable as they respect the criteria commonly used for cavern design. Moreover, combined storage of CO 2 and O 2 in the same cavern, rather than independent storage, would reduce the number of caverns needed and the likelihood of phase changes, but it would require separation of the two substances at the ground surface.

In the energy transition context, salt caverns are probably the most promising storage solution that promotes the development of intermittent renewable energies, due to their flexible and high deliverability . However, their design is still challenging since it should account for their entire lifetime, from rapid cycling exploitation to centuries of abandonment. The key to an optimal design is a constitutive model for rock salt that ensures pertinent short and long-term predictions. In this paper, we confront the results of five experimental campaigns conducted on different salts with existing rheological models. This confrontation proved that the studied models are capable of describing laboratory tests, however their predictions for the long term are either too conservative or overly optimistic. In practice, conservative or optimistic approaches do not ensure the optimal design of the facility. For this reason, we propose a new constitutive model that provides pertinent long-term predictions while interpreting satisfactorily short-term and long-term laboratory tests.

Natural gas storage in salt caverns requires fast injection / withdrawal cycles due to the increasing dynamics of the energy market. High rates induce rapid changes in the internal pressure of the stored gas causing important temperature changes susceptible to damage the rock salt mass. To experimentally observe this, the Starfish project aimed to characterize the damage caused by purely thermal stresses at the surface of a large bloc of rock in the salt mine of Varangeville (France). The objective was to determine the type of failure mechanism involved with repeated cooling stages. Since the salt is favourable to the generation of Acoustic Emissions (AE) and the propagation of stress waves, acoustic monitoring was chosen as one of the methods to follow the impact of the salt cooling. In addition to thermal and mechanical sensors , an acoustic monitoring device consisting of 16 ultrasonic sensors was installed on the free surface and in boreholes . It enabled to record and locate a large number of AE (58,426) located with good accuracy (2.5 cm). Those AE can be correlated to the evolution of salt fracturing. Acoustic activity is very intense at the start of each cooling cycle, then decreases with time to reach a very low level (background) after about 15 days. The average localisation depth reached by the AE is about 90 cm during the first cooling period. For subsequent cooling cycles, this depth is limited to 74 cm. These results show that the first cooling period is decisive, as it contains the strongest and deepest acoustic emissions.

Author(s): Blanco-Martin, L; Rouabhi, A; Billiotte, J; Hadj-Hassen, F; Tessier, B; Hevin, G; Balland, C; Hertz, E | Abstract: High frequency cycling of salt caverns is becoming common practice to meet the needs of energy markets and to foster underground energy storage. In the case of rapid cooling, tensile stresses and thermally-induced fractures can appear in the surrounding rock, with potential detrimental consequences to the integrity of the storage project. To further investigate the effects of rapid cycles on the integrity of rock salt, a thermo-mechanical test was performed in a salt mine. It consisted in cooling rapidly several times a salt surface of 10 m2 (ΔT=−20 °C in about 8 h). Extensive monitoring allowed tracking the thermo-mechanical response of the rock, including possible fracture creation and propagation. Although more research is needed, the test demonstrated that tensile fracturing due to rapid cooling is possible. Thermo-mechanical modeling allowed reproducing fairly well the location, orientation and timing of the first fracture; indeed, fractures should be avoided to ensure cavern integrity, and therefore knowledge about the critical zones where fractures could appear is sufficient at the design stage.

© 2017 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences Laboratory pull-out tests were conducted on the following rock bolts and cable bolts: steel rebars, smooth steel bars, fiberglass reinforced polymer threaded bolts, flexible cable bolts, IR5/IN special cable bolts and Mini-cage cable bolts. The diameter of the tested bolts was between 16 mm and 26 mm. The bolts were grouted in a sandstone sample using resin or cement grouts. The tests were conducted under either constant radial stiffness or constant confining pressure boundary conditions applied on the outer surface of the rock sample. In most tests, the rate of displacement was about 0.02 mm/s. The tests were performed using a pull-out bench that allows testing a wide range of parameters. This paper provides an extensive database of laboratory pull-out test results and confirms the influence of the confining pressure and the embedment length on the pull-out response (rock bolts and cable bolts). It also highlights the sensitivity of the results to the operating conditions and to the behavior of the sample as a whole, which cannot be neglected when the test results are used to assess the bolt-grout or the grout–rock interface.

International audience; A new analytical approach able to predict the mechanical behaviour of fully grouted rockbolts subjected to pull-out tests is proposed in this paper. Input parameters of such approach are: bolt radius, bolt's Young modulus, displacement of the free end of the bolt and the constitutive law of the rockbolt-grout joint interface. The limited circumstances under which it is accurate to determine such constitutive law from pull-out tests are also presented. A solution for the load-displacement curve obtained during pullout tests has been developed and is detailed in the case of a tri-linear bond-slip model. Comparison with experimental results obtained via in situ pull-out tests has led to the validation of this approach

La mise en contact d’une roche argileuse avec l’eau entraine l’apparition d’un gonflement qui joue un role important dans le comportement des ouvrages creuses dans ce type de terrain. Cette deformation est marquee par un caractere tridimensionnel et anisotrope et fait intervenir plusieurs mecanismes comme l’adsorption. l’osmose ou la capillarite.Plusieurs travaux de recherche se sont interesses au gonflement et ont souvent ete controverses en raison de la complexite des phenomenes impliques. Cet article s’inscrit dans le cadre de ces recherches et vise a contribuer a la comprehension du gonflement des roches argileuses lorsqu’elles sont confinees et soumises a l’eau. Pour caracteriser le gonflement et identifier les principaux parametres qui le gouvernent, il etait necessaire, en premier lieu, d’aborder le probleme avec une approche experimentale. De nombreux dispositifs ont alors ete mis au point afin de realiser des essais dans differentes conditions de gonflement.Les resultats experimentaux obtenus ont permis le developpement d’un modele rheologique qui prend en consideration le temps, l’anisotropie et le chargement applique.

International audience; The bolt-grout interface of fully grouted rockbolts has been studied with the aim of determining its constitutive law. For this purpose, axial loadings acting on the bar have been considered and theoretical and experimental research conducted. The theoretical investigations link the response of the surrounding materials (bolt, grout and ground) to that of the interface, which is not directly accessible. Pull-out tests have been carried out to obtain experimental information. Combining the theoretical developments with the test results, the interface variables can be determined. This procedure proves that, in order to study the bolt-grout interface accurately, the behaviour of the surrounding materials should be well known. From the available data, a semi-empirical formulation of the interface response is proposed. The tangential behaviour suggests that friction is not the only component to the shear stress. The normal response, which is more difficult to ascertain, depends on the bolt profile.

International audience; This paper deals with a new macroscopic numerical modelling of the mechanical long-term behaviour of ANDRA's underground research laboratory. The study focuses on the GMR gallery, oriented along the minor horizontal principal stress and located at the main level 490m deep. The simulations are made using the finite element method (FEM). Convergence measurements in this gallery exhibit an important dissymmetry between the vertical and horizontal directions, as well as a significant time effect in the vertical trend. In attempts to both understand the phenomena that lie beneath such dissymmetry and reproduce the experimental data, a modification to Lemaître's creep law has been proposed. The new viscoplastic law takes into account the following aspects: rock transverse isotropy, creep behaviour and rock expansion. The excavation history of the GMR gallery has also been considered in the numerical modelling. The numerical results are very satisfactory for the GMR drift. However, the mechanisms of anisotropic shear and expansion on which the new law is based do not lead to an accurate reproduction of the data measured in the galleries oriented in the perpendicular direction. Therefore, a thorough insight into the mechanical behaviour of the rock mass and into the proposed new law is needed before the latter can be applied to the Callovo-Oxofordian layer.

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Dans cet article, nous etudions l’interface barre-scellement du boulonnage/câblage a ancrage reparti. L’application d’un effort de traction sur la barre permet d’examiner le phenomene de decohesion de l’interface. Des etudes experimentales et theoriques ont ete menees, en conditions statiques. Les etudes theoriques sont utiles pour convertir les variables observables dans les materiaux environnants (barre, scellement, terrain) en variables d’interface, non accessibles directement. Les etudes experimentales, effectuees en laboratoire et in situ , permettent de determiner les facteurs les plus influents sur la reponse de l’interface. La combinaison de ces deux etudes constitue une methode d’acces a la reponse de l’interface barre-scellement. Un exemple d’application de la nouvelle methode est detaille pour une configuration en laboratoire. L’analyse de plusieurs interfaces suggere que la reponse tangentielle n’est pas seulement due au frottement et que la reponse radiale depend fortement du profil de la barre.

Shaly formations are the focus of many research programs and consortia sponsored by petroleum companies and/or waste management organizations; given that they act as seals for oil- or gas-bearing reservoirs or as host rock for underground waste disposals, their integrity (e.g., the possible presence of water-bearing fractures) is a critical factor in risk assessment. To model their rheological properties through time, the observed clastic injectites are used as markers of their mechanical evolution. Aptian–Albian marly formations of the Vocontian Basin (southeast France) are the basis of this study; massive turbidite systems associated with large-scale clastic injectite networks have been described in exceptional outcrops. Field data have permitted the identification of early fracturing in the host formation; the injection of sand is an early event, contemporaneous with the deposition of massive sand bodies. The paleocompaction curve has been calculated, and the porosity evolution of the sediments has been restored from sea floor to about 500 m (1640 ft) burial. Then, the original configuration of dikes can be reconstituted. Boundary conditions of various numerical modeling have been derived from this extensive reliable data set. Numerical static simulations of the behavior of marly formations are presented, testing the possible function of heterogeneous lithology, bedrock geometry, or loading by sudden massive sand deposition; they indicate that early fracturing is physically possible in the presented scenarios. The next step will be to simulate in dynamic conditions the opening and filling of some of these cracks by hydrofracturing. We dedicate this chapter to the memory of our colleague and friend, Stephen T. Horseman.

Langer (1984) stated that reliable extrapolation of the creep equations at low deformation rates can be carried out only on the basis of deformation mechanisms. The micromechanisms that govern salt1 INTRODUCTION1.1 Norton-Hoff lawThe mechanical behavior of salt has given rise to abundant literature. When a constant mechanical load is applied to a salt sample, most authors observe: a steady-state strain rate is reached after some time, it is a nonlinear function of the applied stress, it is sensitive to temperature, and no volume change is observed. The main features of such a steady-state behavior are captured by the NortonHoff law, or d dt Ass ne σp .( )Tσ , ( )Q RT Typical values for the constants n and Q/R range from 3 to 6 and from 3,000 to 10,000 K, respectively. The steady-state strain rate d dte( ) is typically bout 10−10 s−1 for a deviatoric stress ( )σ of 10 MPa and temperature (T) of 300 K. This rate is relatively slow, and during most laboratory tests, the applied stress is larger than 10 MPa.

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The hydration of the shale with an aqueous solution induces a swelling deformation which plays animportant role in the behaviour of the structures excavated in this type of grounds. This deformationis marked by a three-dimensional and anisotropic character and involves several mechanismslike adsorption, osmosis or capillarity.Several researches were dedicated to swelling and were often much debated due to the complexity ofthe implied phenomena. The goal of this thesis is therefore to contribute to a better understandingof shale swelling when the rock is confined and hydrated with an aqueous solution. The main partof the work accomplished was related to the Lorraine shale and to the Tournemire shale.To characterize swelling and to identify the main governing parameters, it was necessary to start theissue with an experimental approach. Many apparatus were then developed to carry out tests undervarious conditions of swelling. In order to facilitate the interpretation of the tests and thereafterthe modelling of the behaviour, the experimental procedure adopted consisted of studying first themechanical aspect and then the chemical aspect of swelling.In the mechanical part, swelling was studied by imposing on the sample a mechanical loading whilemaintaining during the tests the same aqueous solution. The principal parameters which were studiedare the effect of the lateral conditions on axial swelling (impeded strain or constant stress) aswell as the influence of the axial stress on radial swelling. The anisotropy of swelling was studiedby carrying out, for different orientations of the sample, tests of free swelling, impeded swelling anduniaxial swelling. These various mechanical tests allowed to study the three-dimensional anisotropicswelling in all the conditions and to select the most appropriate test to be used in the second phaseof the research.The precise analysis performed to explain the mechanisms behind the swelling of an argillaceous rockwhen it is in contact of water showed that the mechanical response is ruled mainly by electrochemicalphenomena which operate between the solution elements and the clay layers. This importantresult oriented the research to develop better the role of the chemistry in the behaviour. Swellingwas therefore analysed by imposing on the sample a chemical loading while maintaining constantthe axial stress. Monovalent and divalent salts which were used with various concentrations arethe sodium chloride (NaCl), the potassium chloride (KCl) and the calcium chloride (CaCl2). Theforeseen objective was to analyze the effect of the chemical path with decreasing or cyclic concentrationsand to highlight the role of the solution normality, the type of salt and the anisotropy onthe axial swelling.The experimental results obtained allowed the development of a new rheological model which takesinto account the time, the anisotropy, the applied loading and the chemistry of the solution. Thismodel was implemented in a finite element code to simulate simple cases and to prove its validity.; La mise en contact d'une roche argileuse avec une solution aqueuse entraîne l'apparition d'un gonflement qui joue un rôle important dans le comportement des ouvrages creus ́es dans ce type de terrain. Cette déformation est marquée par un caractère tridimensionnel et anisotrope et fait intervenir plusieurs mécanismes comme l'adsorption, l'osmose ou la capillarité. Plusieurs travaux de recherche se sont intéressés au gonflement et ont souvent ́été controversés en raison de la complexité des phénomènes impliqués. Cette thèse s'inscrit dans le cadre de ces recherches et vise à contribuer à la compréhension du gonflement des roches argileuses lorsqu'elles sont confinées et soumises à une solution hydratante. L'essentiel des travaux réalisés dans cette thèse a concerné l'argilite de Lorraine et l'argilite de Tournemire. Pour caractériser le gonflement et identifier les principaux paramètres qui le gouvernent, il était nécessaire d'aborder le problème en premier lieu avec une approche expérimentale. De nombreux dispositifs ont alors été mis au point afin de réaliser des essais dans différentes conditions de gonflement. Afin de faciliter l'interprétation des essais et par la suite la modélisation des comportements observés, la démarche expérimentale adoptée a consisté à étudier le gonflement à partir d'une analyse mécanique suivie d'une analyse chimique. Dans la partie mécanique, le gonflement a été étudié en imposant à l'échantillon des sollicitations mécaniques et en maintenant invariante la solution d'hydratation durant les essais. Les principaux points examinés étaient, d'une part, l'effet des conditions aux limites latérales sur le gonflement axial (déplacement nul ou contrainte constante), et d'autre part, l'influence de la contrainte axiale et son historique de déchargement sur le gonflement radial. L'anisotropie du gonflement a été étudiée en effectuant, pour différentes orientations de l'échantillon, des essais de gonflement libre, de gonflement empêché et de gonflement uniaxial. Cet ́éventail d'essais mécaniques a permis d'étudier le gonflement tridimensionnel anisotrope en passant du gonflement maximal au gonflement nul et de choisir le type d'essai le plus approprié à utiliser dans la suite de la recherche. L'analyse précise effectuée pour expliquer les mécanismes qui sont à l'origine du gonflement a montré que le comportement est surtout régi par des phénomènes électrochimiques qui s'opèrent entre les ions de la solution et les feuillets argileux. Ce résultat important nous a conduit à développer plus en détail dans la partie chimique le rôle de la solution aqueuse. Dans cette partie, le gonflement a été dans ce cas étudié en imposant à un échantillon des sollicitations chimiques tout en maintenant constante la contrainte axiale appliquée durant les essais. Les sels monovalents et le sel divalent utilisés à différentes concentrations sont le chlorure de sodium (NaCl), le chlorure de potassium (KCl) et le chlorure de calcium (CaCl2). L'objectif recherché était d'analyser les effets de l'historique du chemin chimique avec des concentrations décroissantes ou des concentrations cycliques et de mettre en évidence, sur le gonflement axial, le rôle de la normalité de la solution, de chaque type de sel, de l'anisotropie et de la contrainte appliquée. Les résultats expérimentaux obtenus ont permis le développement d'un modèle rhéologique qui prend en considération le temps, l'anisotropie, le chargement appliqué et le chimisme de la solution d'hydratation. Ce modèle a été intégré dans un code numérique et des applications sur des cas simples ont été réalisées pour montrer sa validité.