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A sensitivity study is presented to evaluate the influence of different parameters on the simulation of an underground excavation in the Callovo-Oxfordian (COx) argillaceous formation performed in the Meuse/Haute-Marne underground research laboratory. An elasto-viscoplastic constitutive law representing the characteristic behaviour of indurated mudrocks and stiff clays has been employed. It incorporates anisotropy, strain-softening, creep deformations and dependence of permeability on damage. In addition, a non-local formulation, able to simulate localised deformations objectively, has been incorporated in the analyses. The following features affecting the excavation have been studied: initial stress, strength and stiffness anisotropy, strength parameters, hydraulic and hydromechanical parameters, and scale effects. A simulation reported in a companion paper provides the base case for benchmarking. The results are compared in terms of extent and configuration of the excavation fractured zone, vertical and horizontal tunnel convergences, and the development and evolution of pore pressures in the rock. From the comparisons, an enhanced understanding of the hydromechanical mechanisms associated with underground excavations in COx claystone, and other similar argillaceous materials, has been achieved. We are grateful for the financial and technical assistance of the French national radioactive waste management agency (Andra) to the work presented. The technical assistance of Plaxis is also gratefully acknowledged. The first author has been supported by a Conacyt scholarship (Reg. No. 270190).

This work aims at investigating the effect of aleatoric uncertainty of creep rock properties on the stability of an underground structure. This uncertainty relates to the spatial variability of the mechanical parameters representing the time-dependent behavior of geological rock formation due to the change in its mineralogy. The chosen methodology consists of representing the aleatoric uncertainty of rock properties by random fields, written as correlation functions with respect to the spatial correlation length. The adaptation of the well-known Expansion Optimal Linear Estimationmethod (EOLE) is performed to account for the cross-correlation of the random fields of the viscoplastic parameters of the host rock. Then, the Kriging-based reliability analysis is undertaken with respect to the discretized random fields, which allows elucidating the effect of spatial variability. As an application, the proposed approach is chosen to study the stability in the long-term of a deep double-lined drift within the geological disposal facilities (Cigeo project) conducted by the French National Radioactive Waste Management Agency (Andra). The drift will be excavated in Callovo-Oxfordian (COx) claystone (if the Cigeo project is licensed), considered as a potential host rock for the deep geological nuclear waste disposal in France. The results show that the chosen Kriging metamodel for the reliability analysis can be appropriate for the case of high correlation length represented by a moderate number of random variables (up to about 50) after the discretization of random fields. Further, the consideration of aleatoric uncertainty exhibits a lower probability of exceedance in comparison with the case where spatial variability is ignored. Still, more investigations need to be conducted in the future to conclude this observation.

In the 1980s, HADES (High-Activity Disposal Experimental Site) was the first underground research laboratory (URL) dedicated to the study of the geological disposal of radioactive waste in a deep clay formation, the Boom Clay. It was not until the early 2000s, after a siting process, that ANDRA implemented the Meuse/Haute-Marne URL, in the Callovo-Oxfordian formation at a depth of about 500 m in order to develop the Cigéo project (French industrial centre for geological disposal). ANDRA therefore relied heavily on the work carried out in HADES, through numerous co-operation projects (participation in in situ experiments) both between ANDRA and ONDRAF/NIRAS and SCK CEN (EURIDICE) and/or with Mont Terri consortium, and within European projects (CLIPEX, RESEAL, etc.). This was driven by a dual objective: (1) to prepare its own experimental programmes in the Meuse/Haute-Marne underground laboratory (methodology, experimental devices and protocols, etc.); and (2) to acquire general knowledge on the behaviour of argillaceous rocks, in particular in terms of similarity and differences between the various argillaceous rocks. This paper illustrates the contribution of HADES to the ANDRA programme. This concerns the characterization of the claystone behaviour, host rock and swelling clay-based seals (hydromechanical, thermo-hydromechanical, excavation damaged zone, etc.), and the design and the behaviour of underground structures and seals in deep clay formation (constructability, lining/support, etc.).

Demonstrating the feasibility of constructing tunnels in deep clay formations is an important goal of the Belgian RD&D programme on the geological disposal of radioactive waste. In 2002 a major achievement was reached when the HADES Underground Research Laboratory (URL) in Boom Clay was extended with the construction of the Connecting Gallery. This demonstrated that it is feasible to construct galleries in poorly indurated clays using industrial techniques. To monitor the mechanical behaviour of the gallery and assess its stability, strain gauges were embedded in the segmental gallery lining and prisms were installed on the segments. These sensors provide valuable information that will support the design of future galleries. This paper presents 20 years of monitoring data in the Connecting Gallery and a first analysis of these data in terms of Boom Clay behaviour. In addition, the key findings are compared with those of a similar analysis performed by Andra (the French Radioactive Waste Agency) at the Meuse/Haute-Marne URL. The latter URL is excavated in the Callovo-Oxfordian claystone. The comparison identifies general trends and highlights similarities between the behaviour of tunnels in poorly indurated clay (Boom Clay) and in claystone.

This work aims at proposing the methodology on the basis of the extension of the famous reliability analysis, joining the Kriging and Monte Carlo Simulation (AK-MCS) metamodeling technique for analyzing the long-term stability of deep tunnel support constituted by two layers (a concrete liner covered with a compressible layer). A novel active learning function for selecting new training points enriches the Design of Experiment (DoE) of the built surrogate. This novel learning function, combined with an appropriate stopping criterion, improves the original AK-MCS method and significantly reduces the number of calls to the performance function. The efficiency of this modified AK-MCS method is demonstrated through two examples (a well-known academic problem and the case of a deep tunnel dug in the rock working viscoelastic Burgers model). In these examples, we illustrate the accuracy and performance of our method by comparing it with direct MCS and well-known Kriging metamodels (i.e., the classical AK-MCS and EGRA methods).

The sustainability of geotechnical infrastructures is closely linked with their long-time behavior. In fact, there is not a straightforward procedure to predict this behavior, and very often, the back analyses of observed data are the best tool to understand their long-time response. In-situ observations of drifts constructed in the Callovo-Oxfordian (COx) claystone, the potential host formation for geological radioactive waste disposal, in France exhibit a progressive convergence. These convergence measurements with quite significant dispersions reveal a considerable uncertainty of time-dependent behavior of this argillaceous rock that can strongly affect the transmit loading to liners, hence the long term stability of the drift. Consequently, the uncertain quantification of the creep behavior of COx claystone presents an important task before analyzing the safety of the waste disposal system. In this work, this challenge was conducted by using the well-known Bayesian inference technique. For this aim, on the one hand, the effectiveness of the classical and hierarchical Bayesian techniques to quantify the epistemic and aleatoric uncertainties of the time-dependent behavior of the host rock were investigated using synthetic data. On the other hand, we dealt with the uncertain quantification of the Lemaitre parameters that characterize the visco-plastic behavior of COx claystone thanks to the real data of in-situ convergence measurements of drifts.

To assess the operational capacity of human resources in maternal and child health services, in order to provide equitable and sustainable universal health coverage in Benin, the Workload Indicators of Staffing Need (WISN) study was conducted. Method: A total of 487 health facilities and public hospitals were sampled, representing 75% of the public health facilities. Health professionals involved in maternal and child health care were exhaustively included. Results: Overall, 487 health facilities with 3,870 human resources of all categories were evaluated for their workloads. The analysis shows that the country does not have the necessary manpower to handle the workload. The time spent by the health professional on activities changes according to the type of activity. Finally, it is noted that there is work pressure on health professionals which changes according to the type of activity. Discussion: The shortage situation leads to inequity in the distribution of human resources and is a reason for allocative and technical inefficiency. It is observed that qualified human resources devote little working time to the main activities, which explains the observed high morbidity and mortality rates, particularly for mothers and children. In conclusion, the analysis of the results shows that the pressure of work is greater in rural areas than in urban areas for the professional categories most encountered in rural areas and that the health system is fragile in the country.

International audience; The thermo-hydro-mechanical behavior of the host rock is essential while designing an underground radioactive waste disposal repository, and in particular, while considering the long-term safety of the facility. In 2000, the French National Radioactive Waste Management Agency (Andra) started constructing an underground research laboratory located in the Meuse Haute Marne to carry out a research program aiming to demonstrate the feasibility of constructing and operating a radioactive waste disposal facility in the Callovo-Oxfordian claystone, and to optimize its implementation. To study the thermo-hydro-mechanical effects of the early thermal phase on the clay host rock of a deep repository, Andra has performed various in situ heating tests; one of them is called the TED experiment. The aim of the TED experiment was to measure the evolution of the temperature and pore pressure fields around several heaters and to back-analyze the thermo-hydro-mechanical properties of the Callovo-Oxfordian claystone. Thermal conductivity and heat capacity values were determined based on the back-analysis of the in situ measurements and compared to those measured on samples. The in situ experimental data and numerical model confirm the anisotropic behavior of the claystone. The TED experiment results demonstrate the ability of current models to predict the evolution of temperature and pore pressure in the far field of disposal cells.

Callovo-Oxfordian (COx) claystone has been considered as a potential host rock for geological radioactive waste disposal in France (Cigéo project). During the exploitation phase (100 years), the stability of drifts (e.g. galleries/alveoli) within the disposal is assured by the liner, which includes two layers: concrete arch segment and compressible material. The latter exhibits a significant deformation capacity (about 50%) under low stress (

The Meuse/Haute-Marne Underground Research Laboratory (MHM URL) is an outstanding scientific tool that provides reliable data on the behaviour of Callovo-Oxfordian (COx) claystone. More than 10,000 sensors have been installed in the argillaceous formation to measure rock properties and behaviour under several configurations in order to assess coupled processes. Since 2004, data have been acquired continuously through several measurement campaigns –mainly in galleries at the main level, −490 m (clay unit level –, i.e. UA level), but also in a gallery at −445 m [silty carbonate unit level (USC)]. This experiment has increased understanding of the hydro-mechanical behaviour of claystone and highlight various phenomena. The research program carried out in the MHM URL galleries also is dedicated to technology improvement and demonstration issues of several disposal systems. 1 At MHM URL, the principal horizontal major stress ( σ H ) is oriented at NE150° , and the principal vertical stress ( σ v ) is nearly equal to the principal horizontal minor stress ( σ h ) that is oriented NE065° . The ratio σ H ∕ σ h is close to 1.3 and varies with depth and the rheological characteristics of the respective layers. This paper presents the hydro-mechanical coupling (i.e. interaction between the interstitial water and the solid skeleton) during and after excavation work. The influence of the in-situ stress fields on several types of support was studied for a gallery oriented according to the principal minor horizontal stress ( σ h ). This paper presents an analysis of measurements recorded during and after the construction of an experimental gallery, referred to as the GER, from 2013 to 2015. The GER experimental gallery is an 83-m-long tunnel, in which four different supports were tested: sliding arches; shotcrete; compressible wedges; and poured concrete. Sliding arches, shotcrete and compressible wedges constitute the initial supports that were installed during excavation. The poured concrete was set up about 9 months after the section excavation as a final support, first at the bottom and then at the vault of the gallery. Hydrogeological and geotechnical measurements help to describe the hydro-mechanical response of the surrounding rock mass. Experimental results highlight the anisotropy of the loading from the surrounding rock mass and the influence of the stiffness/flexibility of the support.

Anisotropic mechanical properties of the sedimentary Callovo-Oxfordian clay rock were investigated with triaxial compression and extension, cyclic compression, and creep tests. The tested cylindrical samples differ in bedding orientation. The compression was accomplished by increasing axial stress at constant radial stress. The extension was carried out vice versa: radial stress was increased while axial stress was kept constant. Moreover, extension was also achieved by simultaneously increasing radial stress and decreasing axial stress under constant mean stress. Five independent elastic parameters were obtained at different deviatoric stresses during cyclic loading-unloading compressions. The deformation and strength were determined in relation to the load direction inclined to bedding and in relation to the load paths. The claystone exhibits elastoplastic stress-strain behaviour with volume compaction until failure. The strength is dependent on both load path and load direction to the bedding. For a given major load direction, the compressive strength is higher than the extensional one and the lowest strength occurs by extension at constant mean stress. In each load path, the maximum strength values are reached parallel and normal to the bedding, while the minimum occurs at the load orientation of about 45° during compression and of about 30° during extension. The elastic stiffness increases with deviatoric loading due to hardening. The deformability is time dependent.

The paper describes the performance, observations and numerical interpretation of a full-scale in situ heating test conducted on Callovo-Oxfordian (COx) claystone in the Meuse / Haute-Marne (MHM) Underground Research Laboratory (URL) simulating a heat-emitting, high-level radioactive waste disposal concept. In the experiment, five heaters 3 m-long are placed in the axis of a microtunnel excavated in COx claystone to simulate the heat production of radioactive waste. The test is fully instrumented, and attention is focused on the near-field region's thermo-hydro-mechanical (THM) behaviour consisting of the casing surrounding the heater and the host formation (COx claystone). The interpretation of the test is assisted by the performance of a numerical analysis based on a coupled formulation incorporating the relevant THM phenomena. The calculations have used a constitutive law especially developed for this type of material. Initial and boundary conditions for analysis as well as material parameters are determined from a comprehensive field and laboratory experimental programme. The paper presents and discusses the thermal, hydraulic and mechanical observations in COx claystone, casing and an annular air-filled gap between the host formation and the casing. Special attention is also paid to the mechanisms involved in the interface between the rock and the casing. Heating has been applied in two stages; a cooling stage (also applied in steps) completes the experiment. The numerical analysis performed has proved able to represent the progress of the experiment very satisfactorily. By performing the 3D numerical analysis, it has been possible to incorporate anisotropies of material parameters and of in situ stresses. The performance and analysis of the in situ test have significantly enhanced the understanding of a complex THM problem and have proved the capability of the numerical formulation to provide adequate modelling capacity. The technical and financial support of the Agence Nationale pour la Gestion des Déchets Radioactifs (ANDRA) is gratefully acknowledged.

Time-dependent rock behavior can significantly affect the design and the construction method of tunnel support lining. As an innovation, a concrete liner covered with a compressible layer is thus of great interest to reduce the underground space project costs. Indeed, the compressible material usually exhibits very high deformability under oedometric loading (30–60% volumetric deformation under a weak variation in axial stress). This helps to absorb the convergence of the excavated wall of the squeezing rock, and thus limit the transmission of stress to the inner concrete lining. This study firstly aims at deriving a closed-form solution for a deep-circular tunnel excavated within the viscoelastic Burger rock and supported by a double-layer concrete/compressible material. The inner concrete layer is assumed to be linear elastic, while the outer compressible layer is described by a tri-linear elastic model. The analytical solution is derived under the integral equation form. Secondly, the effects of uncertainty of time-dependent mechanical properties of host rock on the failure probability of tunnel for a period of 100 years are studied by introducing the closed-form solution into the well-known Kriging-based reliability analysis AK-MCS (Active learning reliability method combining Kriging and Monte Carlo Simulation) method. Notably, the benefit of the compressible layer is highlighted from the reliability analysis.

The Andra’s (French National Agency for Radioactive Waste Management) Meuse / Haute-Marne Underground Research Laboratory in Bure is currently under extension (4th extension), with the excavation of new galleries having different shapes and support types. The galleries are excavated in the Callovo-Oxfordian (COx) claystone, with a creeping behaviour, at 490 m depth. The continuum rheological model which has been considered (among the available ones) is an elasto-visco-plastic model with the Hoek-Brown failure criterion and the Lemaitre creep law. The choice of the rock parameters to be used for the design studies of the 4th extension (aiming to verify the stability of support systems over a service duration of 20 yr) has been based on two sets, defined in previous studies and calibrations. The in-situ measurements, provided by the R&D division of Andra, of three galleries and a shaft, excavated about 10 yr ago, have been back-analysed with these two sets of parameters. The comparison of results led to the choice of the most suitable set of parameters for the design of the new extension galleries.

In France, a deep geological disposal for high-level radioactive waste (HLW) and intermediate level long life radioactive waste (IL-LLW) called Cigéo is planned to be constructed in a deep Callovo-Oxfordian claystone (COx) formation, if it is authorized. The heat emitted from the waste leads to a temperature increase in the low permeability host porous formation, which induces a pore pressure increase essentially due to the difference between the thermal expansion of the pore water and the solid skeleton. This study aims at assessing the effect of nonlinear behavior of COx, especially creep, on the THM response of the HLW repository. Different approaches, from perfectly MohrCoulomb model and simplified time-dependent models (power and Norton) to an advanced model, have been considered. These approaches lead to common conclusions that (1) the creep reduces the pore pressure increase compared to poro-elastic approach; (2) the nonlinear instantaneous response in the near-field resulting from cell drilling does not affect the THM response in the far field and (3) the thermal load does not induce any supplementary damage of the host rock

Affirmant lors des debats preparatoires a l’adoption de la Constitution du 4 octobre 1958 que « la Republique ne peut etre a la fois une et indivisible et multiple et divisible », Leopold Sedar Senghor entendait mettre en exergue aussi bien le caractere fondamental du principe d’unite que la primaute de l’indivisibilite sur le pluralisme, primaute resultant de leurs « champs d’application respectifs ». Pendant longtemps en effet, « le pluralisme domine la sphere sociale » ou il reste « enferm...

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Nous sommes heureux de présenter ce nouveau numéro des Cahiers de la recherche sur les droits fondamentaux. Il donne aux lecteurs l’occasion de retrouver la teneur des communications faites au colloque « Pouvoirs exceptionnels et droits fondamentaux » organisé par le CRDFED et Gilles Armand à Caen à la fin de l’année 2007. Le lecteur pourra s’apercevoir de ce que les questions posées par un tel sujet n’épuisent certainement pas le sujet, et même, appellent d’autres réflexions. Notamment, émer...

Dans l’un des passages les plus celebres de son œuvre De l’esprit des lois, Montesquieu a pu affirmer « qu’il y a des cas ou il faut mettre, pour un moment, un voile sur la liberte, comme l’on cache les statues des dieux ». Cette affirmation correspond parfaitement a l’etat d’exception au sens classique, « entendu comme un moment pendant lequel les regles de droit prevues pour des periodes de calme sont transgressees, suspendues ou ecartees pour faire face a un peril ». Les droits et les libe...

Depuis que dans des conclusions restees celebres, Bruno Genevois a mis l’accent sur la necessite du « dialogue des juges », le theme n’a cesse d’agiter la pensee des juristes, convaincus que ce dialogue est indispensable dans un univers marque par l’interdependance et la complexite croissantes des systemes juridiques. Le droit des etrangers est un des domaines dans lesquels cet enchevetrement apparait le plus net. Les raisons en sont multiples et biens connues : d’un point de vue externe, dev...

International audience; Continuous field monitoring during drifts excavation at the Meuse/Haute-Marne Underground Research Laboratory showed anisotropic hydromechanical responses, which are mainly evidenced in: (1) pore pressure field around the drifts with zones of marked overpressure; (2) the development of a dissymmetrical fractured zone induced by the excavation. These observations suggest that in addition to the initial stress state, the inherent anisotropy of the Callovo-Oxfordian claystone plays a key role in the response of rock formation. Numerical modelling show that inherent elastic anisotropy is not adequate to fully explain the pore pressure evolution during excavation. This paper aims to show and explain qualitatively and quantitatively the main trends of the excavation induced pore pressure evolution around drifts. First, a qualitative analysis is performed, based on a closed-form solution of elastic fields around an elliptical opening (in order to simulate fractured zone shape), embedded in a transversely isotropic rock. Then, a coupled poro-elasto-plastic analysis is performed, by taking into account a perfect poro-elasto-plastic behavior for both the intact rock and the induced fractured zones with different plastic parameters. It is shown that upon the determination of extension and shape of fractured zone, overpressures induced by the excavation can be well reproduced.

Si le juge administratif exerce un contrôle normal aussi bien sur les décisions d’octroi, de retrait que de suspension de l’agrément des assistants maternels, la décision de suspension se différencie du retrait dans la mesure où il s’agit d’une mesure provisoire, prise dans l’urgence afin de sauvegarder l’intérêt de l’enfant et qui, pour cette raison, a une durée qui ne peut en aucun cas excéder une période de quatre mois, laquelle n’est pas renouvelable. Cependant, il semble que la jurisprudence la plus récente soit marquée par la volonté d’unifier les conditions de la suspension et du retrait de l’agrément des assistants maternels. If the administrative magistrate exercises normal control over decisions of approval, of withdrawal and of suspension of the authorisation of foster parents, the decision concerning suspension differs from that of withdrawal in as far as it is a temporary measure, taken in an emergency in the child’s interest and which, for this reason, can in no case last more than four months and cannot be extended. However, it appears that the most recent case law reveals a wish to standardise the conditions for suspension and withdrawal of the authorisation of foster parents.

In the context of feasibility study for geological disposal of radioactive waste, this work focuses on numerical modeling of hydromechanical response and induced damage zones around an experimental gallery at the underground research laboratory (URL) at Bure in France. A new phase-field method is first proposed by considering two independent damage fields in order to easily describe both tensile and shear cracks. The phase-field method is extended to saturated porous media by incorporating the effect of fluid pressure. The proposed method is implemented in a finite element code and applied to the experimental gallery. The evolutions of hydromechanical responses and induced damaged zones are analyzed in both excavation and post-excavation phases. Numerical results are compared with experimental observations and measurements. It is found that the proposed method is able to well describe the main features of hydromechanical responses and damage processes such as tensile and shear cracked zones.

In France, a deep geological disposal for high level radioactive waste (HLW) and intermediate-level long-lived radioactive waste (ILW-LL) called Cigeo is planned to be constructed in a deep Callovo-Oxfordian claystone (COx) formation. The heat released from the HLW packages leads to a temperature increase in the host rock, which causes a pore pressure increase essentially due to the difference between the thermal expansion of the pore water and the solid skeleton. The low permeability of the COx and its relative rigidity inhibit the discharge of the induced pressure build-up. Moreover, thermal loading also induces thermo-mechanical stresses within the formation. The French National Radioactive Waste Management Agency (Andra) participated in the DECOVALEX-2019 project (Task E) to model the Thermo-Hydro-Mechanical (THM) responses of a benchmark exercise inspired of a HLW repository based on the French concept. This paper aims at studying the THM behavior of the HLW repository by taking into account the inherent spatial variability of the properties of the host rock through thermo-poro-elastic numerical simulations. Only the most influential parameters were selected to perform the spatial variability analysis by using Monte Carlo simulations coupled with the Random Finite Element Method . The selection of the most influential parameters was based on two parametric sensitivity analyses consisting in computing the Sobol indices, which determine the contribution of each input parameter to the overall model output variance. The temporal evolution of the Terzaghi effective stress in the far field is defined as indicator of the influence of each parameter on the THM response.

The French National Radioactive Waste Management Agency (Andra) is in charge of studying the disposal of high-level and intermediate-level long-lived waste (HLW and ILW-LL) in a deep geological repository (Cigéo project) within the host formation is the Callovo-Oxfordian claystone (COx). The heat emitted from waste packages induces a thermo-hydro-mechanical (THM) coupling within the structural elements and the host rock. This study focuses on the behavior of the concrete lining of an ILW-LL cell subjected to THM loading during its construction and operational phases. The mechanical behavior of the host rock is represented by an elasto-visco-plastic model taking into account the anisotropies in stiffness and strength. The coupled THM formulation is based on the Biot theory. Different simulations including full THM coupling and HM coupling with or without creep behavior of COx claystone have been performed to show the effect of the thermal load (generated by the waste packages), of the water seepage and of the creep strain of the host rock on the stress evolution in the concrete liner. The results show the preponderant role of the creep strain of COx claystone on the stress state of the liner during the operational phase, while the effect of the heat loading is moderate and that of the seepage is not significant.

Author(s): Seyedi, DM; Plua, C; Vitel, M; Armand, G; Rutqvist, J; Birkholzer, J; Xu, H; Guo, R; Thatcher, KE; Bond, AE; Wang, W; Nagel, T; Shao, H; Kolditz, O | Abstract: The coupled Thermo-Hydro-Mechanical (THM) behavior of the Callovo-Oxfordian claystone (COx) is of great importance for the design and safety calculations of the high-level radioactive waste disposal project in this potential host rock in France. The heat emitted by the waste causes a pore pressure increase within the surrounding rock essentially due to the differential thermal expansion of the pore water and the solid skeleton. The low permeability of the COx and its relative rigidity inhibits the discharge of the induced pressure build-up. Moreover, thermal loading may provoke thermo-mechanical stresses within the formation due to mechanical confinement by the rigidity of the surrounding host rock. An important research program has been conducted by the French National Radioactive Waste Management Agency (Andra) since 2003 in order to investigate the THM response of the COx under thermal loading, through laboratory tests, in-situ experiments, model development and numerical modeling. Within Task E of the DECOVALEX-2019 project, five research teams investigated upscaling THM modeling from a small-scale in-situ experiment (TED) to a full-scale in-situ experiment (ALC). The upscaling modeling started with a verification test to validate the numerical codes. Then, an interpretative modeling of the TED experiment was performed to calibrate the THM parameters of the COx. Finally, the calibrated THM parameters were used for a blind prediction of the ALC experiment. The modeling teams each adopted a thermo-poro-elastic approach which yielded satisfactory results. The blind prediction of the temperature field showed an overestimation of less than 2 °C which was considered acceptable. On the other hand, pore pressure was well predicted only in the direction parallel to the bedding whereas the slow dissipation of the pore pressure in the direction perpendicular to the bedding was not captured by any of the modeling teams – which remains an open question of the present study.

International audience; Continuous monitoring around drifts excavated in the Underground Research Laboratory (URL) of The French National Radioactive Waste Management Agency (Andra) in Callovo Oxfordian claystone revealed the development of a fractured zone (extensional and shear fractures) induced by the excavation. Moreover, the field monitoring during the excavation showed an anisotropic pore pressure field around the drifts with zones of marked overpressure. For drifts parallel to the horizontal major principal stress, even though the initial stress state in the drift section is quasi-isotropic, the pore pressure evolution and the mechanical response are anisotropic. These observations suggest that the intrinsic anisotropy of the material plays a key role in the response of rock formation. A poroelastic analysis of the pore pressure change induced by drift excavation is performed. The principal objective is to simulate the main trends of the pore pressure evolution with a simple model taking into account the elastic anisotropy of the material. It is shown that depending upon the permeability and the degree of anisotropy of the rock, strong overpressures can be induced by the excavation. Furthermore, it is observed that the distribution of overpressures around drifts depends also on the drifts orientation. Finally, an analysis of the onset of failure shows the key role of the hydro-mechanical coupling on the extension of the failed zone around the drifts.

In the context of radioactive waste disposal, an underground research laboratory (URL) is a facility in which experiments are conducted to demonstrate the feasibility of constructing and operating a radioactive waste disposal facility within a geological formation. The Meuse/Haute-Marne URL is a site-specific facility planned to study the feasibility of a radioactive waste disposal in the Callovo-Oxfordian (COx) claystone. The thermo-hydro-mechanical (THM) behaviour of the host rock is significant for the design of the underground nuclear waste disposal facility and for its long-term safety. The French National Radioactive Waste Management Agency (Andra) has begun a research programme aiming to demonstrate the relevancy of the French high-level waste (HLW) concept. This paper presents the programme implemented from small-scale (small diameter) boreholes to full-scale demonstration experiments to study the THM effects of the thermal transient on the COx claystone and the strategy implemented in this new programme to demonstrate and optimise current disposal facility components for HLW. It shows that the French high-level waste concept is feasible and working in the COx claystone. It also exhibits that, as for other plastic clay or claystone, heating-induced pore pressure increases and that the THM behaviour is anisotropic.

Thermal effects on the Callovo-Oxfordian and Opalinus clay rocks for hosting high-level radioactive waste were comprehensively investigated with laboratory and in situ experiments under repository relevant conditions: (1) stresses covering the range from the initial lithostatic state to redistributed levels after excavation, (2) hydraulic drained and undrained boundaries, and (3) heating from ambient temperature up to 90 °C–120 °C and a subsequent cooling phase. The laboratory experiments were performed on normal-sized and large hollow cylindrical samples in various respects of thermal expansion and contraction, thermally-induced pore water pressure, temperature influences on deformation and strength, thermal impacts on swelling, fracture sealing and permeability. The laboratory results obtained from the samples are consistent with the in situ observations during heating experiments in the underground research laboratories at Bure and Mont-Terri. Even though the claystones showed significant responses to thermal loading, no negative effects on their favorable barrier properties were observed.

The Callovo-Oxfordian claystone (COx) is considered as a potential geological formation to host an industrial radioactive waste repository in France. A detailed understanding of the thermo-hydro-mechanical (THM) behavior of the COx is a key issue for design of different repository structures and the safety calculations of the project. More particularly, numerical modeling of induced fracture networks around drifts excavated at the main level of the Andra’s Meuse/Haut-Marne Underground Research Laboratory (M/HM URL) and short and long term behavior of the COx around these drifts are of great interest. Several constitutive models have been developed/used in the framework of the R&D and simulation programs of Andra. A model benchmark exercise has been launched since 2012 to provide an overall view of the developed models regarding the in situ observations. In this view, two series of test cases, respectively at material point scale and at drift excavation scale are defined. Different kinds of constitutive models based on the elasto-visco-plasticity concept, continuum damage mechanics, the rigid block spring method and two-scale computational homogenized model (CHM) are used within this exercise. The obtained results show that accounting for material anisotropy and strain localization treatment techniques can improve the obtained results when elasto-visco-plastic models are used. Damage mechanics based approaches and methods accounting for discontinuities through discrete elements provide also interesting insights especially when fracturing processes must be modeled. However, more efforts are necessary to improve the robustness of these kinds of approaches in the complex context of COx response to excavation works.

This paper addresses the microstructure change induced by swelling for natural stiff Teguline clays. The predominant clay mineral measured by X-ray diffractometry was identified to be illite and no swelling clay minerals were found. Significant swelling occurs upon wetting, illustrating the process of suction release from a nearly fully saturated condition. Mercury intrusion porosimetry (MIP) and scanning electron microscopy were used to identify the change in microstructure with swelling during wetting. It is found that the soil swelling mainly leads to an increase of macropores (0.15–350 μm), and a slight decrease of micropores (0.006–0.15 μm) and inaccessible pores (350 μm). Furthermore, swelling was found to occur in the direction perpendicular to the bedding plane, indicating an anisotropic swelling behaviour. The creation and development of cracks during wetting were also investigated. It appears that most cracks caused by swelling have the size of macropores (0.15–350 μm) identified by the MIP test. These findings call enough attention to the significant change in microstructure by wetting-induced swelling that can strongly influence the thermohydromechanical properties of stiff clays.

International audience; Production of energy from nuclear power plants generates high-level radioactive nuclear waste, harmful during dozens of 1000 years. Deep geological disposal of nuclear waste represents a reliable solutions for its safe isolation. Confinement of radioactive wastes relies on the multi-barrier concept in which isolation is provided by a series of engineered (canister, backfill) and natural (host rock) barriers. Few underground research laboratories have been built all over the world to test and validate storage solutions. The drilling of disposal drifts may generate cracks, fractures/strain localisation in shear bands within the rock surrounding the gallery especially in argillaceous rocks. These degradations affect the hydro-mechanical properties of the material, such as permeability, e.g., creating a preferential flow path for radionuclide migration. Hydraulic conductivity increase within this zone must remain limited to preserve the natural barrier. In addition, galleries are currently reinforced by different types of concrete supports such as shotcrete and/or prefab elements. Their purpose is twofold: avoiding partial collapse of the tunnel during drilling operations and limiting convergence of the surrounding rock. Properties of both concrete and rock mass are time dependent, due to shotcrete hydration and hydro-mechanical couplings within the host rock. By the use of a hydro-mechanical coupled finite-element code with a second-gradient regularization, this paper aims at investigating and predicting support and rock interactions (convergence and stress field). The effect of shotcrete hydration evolution, spraying time, and use of compressible wedges is studied to determine their relative influence.

This paper is devoted to the study of the Thermo-Hydro-Mechanical (THM) responses of a porous rock with low permeability under thermal loading in the context of deep geological disposal of radioactive waste. To this aim, numerical simulations of a benchmark exercise of a hypothetical high-level radioactive waste (HLW) repository were performed. This benchmark exercise considered as a host formation the Callovo-Oxfordian claystone (COx), which has been selected for a deep geological disposal in France. Within the framework of the DECOVALEX-2019 project, five modelling teams (Andra, LBNL, NWMO, Quintessa, UFZ/BGR) adopted a thermo-poro-elastic approach and proposed different 3D representations of the HLW repository. The differences between the teams consisted mostly in the simplification of the geometrical model and the interpretation of the boundary conditions. Numerical results for temperature, pore pressure , and effective stress evolution in the far field (i.e., at the mid-distance of two HLW cells) were compared between the teams, to quantify the impact of modelling simplifications/assumptions for the assessment of the HLW repository. The THM behaviour of the COx formation in the near field (i.e., excavation damaged zone around the HLW cells) is not the objective of this study. Moreover, plane strain conditions were considered and evaluated in comparison to 3D modelling. Key parameters influencing the THM responses of the HLW repository were assessed by both mono- and multi-parametric analyses. Spatial variability analyses of THM parameters were also carried out to study the influence of the spatial correlation length on the Terzaghi effective stress and to estimate its probability distribution. The conclusions of this study provide reliable numerical techniques for modelling large-scale deep geological disposals and deduce the main behavior of the HLW repository.

This study is part of numerical simulations performed on an in situ heating test conducted by the French National Radioactive Waste Management Agency (Andra) at the Meuse/Haute-Marne Underground Research Laboratory (URL) to study the thermal-hydromechanical behavior of the host Callovo-Oxfordian COx claystone in quasi real conditions, through the international research project DECOVALEX. The emphasis is put on the pore pressure increase generated by the heat released from high level radioactive waste and the consequence on the damage evolution of the host rock. A phase-field method is proposed to describe the evolution of damaged zones around the heating borehole. Both tensile and shear cracks are taken into account. The evolution of damage is coupled with temperature variation, rock deformation, and fluid pressure change. Moreover, the structural anisotropy of elastic properties, permeability, and heat conductivity of the host rock is taken into account. Numerical results are compared with in-situ measurements.

Within the context of deep geological radioactive waste disposal, the French National Radioactive Waste Management Agency (Andra) is conducting a research program including in-situ experiments at the Meuse/Haute-Marne Underground Research Laboratory (MHM URL), which aims to demonstrate the feasibility of constructing and operating a High Level Waste (HLW) disposal facility in the Callovo-Oxfordian (COx) claystone formation and to improve it. ALC1604 experiment is an in-situ heating test reproducing a full-scale HLW disposal cell. Heating devices were placed in the last 15 m of a 25 m long steel cased micro-tunnel to mimic the heat emitted by the HLW packages. The present experiment allows to study the response of the cell and the surrounding rock under thermal loading. More specifically, this experiment studied the thermo-mechanical (TM) behavior of the steel sleeve, equipped with strain gauges, displacement sensors, temperature sensors, etc., and monitored the evolution of the annular space (the gap between the sleeve and the rock). It also studied the thermo-hydro-mechanical (THM) behavior of the near/far field rock through pore pressure and temperature measurements installed in peripheral boreholes. The TM response of the steel sleeve and the THM response of the surrounding rock are numerically reproduced and the chosen THM parameters are compared with previous small-scale in-situ experiments conducted at the MHM URL in order to improve the reliability of the material parameters of the COx. The lessons learned from this experiment has provided valuable feedback towards implementing new full-scale heating experiments consistent with a new benchmark concept. DECOVALEX is an international research project comprising participants from industry, government and academia, focusing on development of understanding, models and codes in complex coupled problems in sub-surface geological and engineering applications; DECOVALEX-2019 is the current phase of the project. The authors appreciate and thank the DECOVALEX-2019 Funding Organizations Andra, BGR/UFZ, CNSC, US DOE, ENSI, JAEA, IRSN, KAERI, NWMO, RWM, SÚRAO, SSM and Taipower for their financial and technical support of the work described in this report. The statements made in the report are, however, solely those of the authors and do not necessarily reflect those of the Funding Organizations. The experimental work presented in this article has received funding from the European Atomic Energy Community's Seventh Framework Program under Grant Agreement n◦269905, the LUCOEX project. The financial support is gratefully acknowledged.

This paper summarises the numerical and experimental studies of brittle, hollow, cylindrical particles, called shells. It addresses the influence of shell properties both at the particle and assembly scales. Extreme compressibility has been recorded in the oedometer tests. Due to the large internal porosity of the shell, the breakage phenomena lead to highly compressive deformations with a significant stress dissipation. Using the Discrete Element Method (DEM), we have investigated in depth the micro-mechanical phenomena governing this macroscopic response. By quantifying the breakage and separating the double-porosity of the material, the foundations of a future constitutive model have been established throughout a simple prediction model applicable to the engineering practice.

Author(s): Xu, H; Rutqvist, J; Plua, C; Armand, G; Birkholzer, J | Abstract: We apply thermoporoelasticity and a sequentially coupling technique for modeling thermally-driven coupled Thermo-Hydro-Mechanical (THM) processes in tight claystone. A THM benchmark case with a corresponding analytic solution for thermoporoelasticity under a constant heat loading verifies the model. Thereafter, two in situ heating experiments are simulated for model validation: a smaller-scale heating experiment (TED experiment) and a larger-scale experiment (ALC experiment) in Callovo-Oxfordian (COx) claystone at the Meuse/Haute-Marne underground research laboratory in France. The model exhibits good performance to match the observed temperature and pore pressure evolution for the smaller-scale TED experiment. For the larger-scale ALC experiment, general trends of thermal-pressurization are captured in the modeling, but pressure is underestimated at some monitoring points during cool-down. This indicates that the THM response in the field may be affected by the variability of rock's properties or irreversible or time-dependent mechanical processes that are not included in the current thermoporoelastic model. The main contributions of this work are as follows: (1) we verify and validate the numerical simulator, TOUGH-FLAC, to be a valuable coupled THM modeling tool; (2) prove that the laboratory determined material parameters can be used as reference values for upscaling experiments. However, to better identify and quantify THM processes with modeling of in situ tests, more emphasize should be dedicated to obtaining high-quality mechanical deformation data.

International audience; In this study, we analyzed the influence of the excavation size and the sequence of excavation on the convergence evolution in drifts excavated in Callovo-Oxfordian claystone. The drifts, which are part of the Underground Research Laboratory of the French National Radioactive Waste Management Agency (ANDRA), had diameters ranging between 0.7 m and 6.3 m. The measurements showed an anisotropic convergence with the maximum and minimum values in horizontal and vertical directions. Using a semi-empirical law, convergence evolution was fitted independently for each drift. The results show that the values for the parameters describing the time-dependent properties of the system rock-support depended upon the time elapsed for the support installation and the rate of excavation. For drifts following the same sequence of excavation, these parameters did not depend upon the size of the excavation. Finally, the analysis of a drift cross section enlargement showed that the convergence evolution was more isotropic and that the values for the parameters describing the time-dependent properties were lower, suggesting that overexcavation could limit the delayed response of the ground.

International audience; Within the framework of feasibility studies for a reversible, deep geological repository of high-and intermediate-level long-lived radioactive waste (HLW, IL-LLW), the French National Radioactive Waste Management Agency (Andra) is investigating the Callovo-Oxfordian (COx) formation near Bure (northeast part of France) as a potential host rock for the repository. The hydro-mechanical (HM) behaviour is an important issue to design and optimise different components of the disposal such as shaft, ramp, drift, and waste package disposal facilities. Over the past 20 years, a large number of laboratory experiments have been carried out to characterise and understand the HM behaviours of COx claystones. At the beginning, samples came from deep boreholes drilled at the ground surface with oil base mud. From 2000 onwards, with the launch of the construction of the Meuse/Haute-Marne Underground Research Laboratory (MHM URL), most samples have been extracted from a large number of air drilled boreholes in the URL. In parallel, various constitutive models have been developed for modelling. The thermohydro-mechanical (THM) behaviours of the COx claystones were investigated under different repository conditions. Core samples are subjected to a complex HM loading path before testing, due to drilling, conditioning and preparation. Various kinds of effects on the characteristics of the claystones are highlighted and discussed, and the procedures for core extraction and packaging as well as a systematic sample preparation protocol are proposed in order to minimise the uncertainties on test results. The representativeness of the test results is also addressed with regard to the in situ rock mass.

International audience; The Callovo Oxfordian clay-rock (COx) is studied in France for the disposal of radioactive waste, because of its extremely low permeability. This host rock is governed by a hydromechanical coupling of high complexity.This paper presents an experimental study into the mechanisms of water uptake in small, unconfined, prismatic specimens of COx, motivated by the comprehension of cracking observed during concrete/COx interface sample preparation. Water uptake is monitored using both x-ray tomography and neutron radiography, the combination of these imaging techniques allowing material deformation and water arrival to be quantified respectively.Given the speed of water entry and crack propagation, relatively fast imaging is required: 5 minute x-ray tomographies and ten-second neutron radiographies are used. In this study, pairs of similar COx samples from the same core are tested separately with each imaging technique. Two different orientations with respect to the core are also investigated. Analysis of the resulting images yields with micro-and macro-scale insights into hydro-mechanical mechanisms to be obtained. This allows the cracking to be interpreted as a rapid breakdown in capillary suction (supposed large both to drying and rebound from in-situ stress state) due to water arrival, which in turn causes a loss of effective stress, allowing cracks to propagate with ease, which in turn deliver water further into the material.

This study focuses on highly compressible granular material incorporated in novel tunnel-lining technology, precisely, the prefabricated tunnel segments called voussoirs. The material composed of hollow, brittle, tube-shaped particles were designed such that the crushing of the constituent particles results in high material compressibility. This paper is essentially dedicated to discrete-element simulations that involve both the breakage of the particles at micro scale and the resulting effects on macro scale. Firstly, a 3D model was proposed in order to adequately reflect the complex geometry and the breakage manner. In applied strategy, the tube-shaped particle is modelled as a cluster of bonded, rigid, sphero-polyhedral sectors. Then, the identification of the parameters that control the mechanical response and the strength of the particles is presented using a radial compression test. This step was supported by laboratory experimental tests. Finally, six assemblies of cluster under oedometric loading were studied by means of Discrete Element numerical simulations. We analysed the influence of the sample size on the evolution of particles breakage and void ratios. This analysis resulted in the definition of new framework for void ratio and a model capable of predicting breakage as a function of the strains.

Les epoux B. demandent au tribunal de condamner le conseil general de l’Eure a reparer le prejudice moral subi par eux-memes et par leur fille ainee a l’occasion du suicide de leur fille cadette. Cette derniere, confiee a l’aide sociale a l’enfance du departement a la suite de fugues repetees, s’etait enfuie de l’hopital ou elle etait soignee apres une tentative de suicide. Violee lors de cette fugue par des pensionnaires d’un autre foyer departemental de l’enfance, elle se suicide apres avoir ete auditionnee dans le cadre de cette affaire. Le rapporteur public, apres avoir rejete la prescription quadriennale invoquee par le defendeur, conclut a la responsabilite du conseil general de l’Eure et demande au tribunal de le condamner.