[en] The model presented in this paper is an adaptation of a model developed at the LaEGO for modelling poro-mechanical behaviour of argilites type rocks, allowing to account for anisotropy. (authors)

[en] Document available in extended abstract form only. Understanding the mechanisms controlling the advective movement of gas and its potential impact on the repository and host rock is important to both performance assessment and the long-term prediction of the repositories evolution. In a clay-based geological disposal facility (GDF), four primary phenomenological models can be defined to describe gas flow: (i) gas movement by diffusion and/or solution within interstitial fluids along prevailing hydraulic gradients; (ii) gas flow in the original porosity of the fabric, commonly referred to visco-capillary flow; (iii) gas flow along localised dilatant pathways (micro-fissuring) which may or may not interact with the continuum stress field; and (iv) gas fracturing of the rock similar to that performed during hydrocarbon stimulation exercises. To investigate which mechanism(s) control the advective movement of gas, two independent experimental studies on Callovo-Oxfordian clay-stone (COx) have been undertaken at the British Geological Survey (BGS) and Laego-Ensg Nancy. A bespoke triaxial apparatus, christened the stress path permeameter (SPP), was designed and constructed at the BGS. The SPP was specifically manufactured to be able to resolve very small volumetric (axial and radial) strains potentially associated with the onset of gas flow. To this end, three pressure-balanced dash-pots were located around the mid-plane of the sample, providing a continuous record of subtle variations in sample diameter during testing. Axial strain was recorded using a digital micrometer. Experiments were performed on preserved test material with a start saturation of 96%. At the start of testing the sample was loaded to the in situ conditions at Bure with a confining pressure of 12.5 MPa, axial stress of 13 MPa and a pore pressure of 4.5 MPa. The initial stage of testing was designed to re-saturate the sample fully and lasted 47 days. The sample exhibited a negative volumetric strain due to swelling. A constant head hydraulic tests was subsequently performed in order to both remove any residual gas from the sample and to define the baseline hydraulic properties of the sample; this stage of testing lasted 79 days. Gas testing began on Day 131, with a constant-flow pressure ramp that raised injection pressure from 4.5 to 9.5 MPa over a 35 day period. Pressure was held constant for 25 days and no indication of gas flow was seen. Therefore a second pressure ramp of 22 days duration was initiated, raising gas injection pressure to 10 MPa. Pressure was held constant for 26 days and again no evidence of gas flow was seen. A final pressure ramp raised gas injection pressure to 10.5 MPa over a 19 day period. Therefore it took a total of 128 days to carefully raise injection pressure from in situ levels to that necessary to initiate gas flow. Gas migration was seen to result in an accelerated dilation at the midplane that cannot be described by the mechanical response of a change in effective stress. The sample behaviour suggests that gas has migrated along dilational pathways. Marked deformation occurred following the onset of gas flow with a total of 42 microns of length dilation occurring and an average radial dilation of approximately 15 microns. This represents a total volumetric strain of 0.035 % or a 71 μl change in sample volume. During the remainder of the gas tests, the radial strain trace exhibited the same functional form as that for the outflow of gas from the sample, providing conclusive proof that gas flow is accompanied by dilation of the COx. A complimentary study performed at Laego-Ensg Nancy used a 38 mm diameter and 76 mm length sample of COx, which was fully saturated under an isotropic stress of 12 MPa close to the in situ state of stress for 4 months. Axial and radial strains were measured using strain gauges glued to the sample and gas and water fluxes and pressures were also monitored. An initial gas pressure of 4 MPa was applied to the sample for 24 days. The pressure downstream of the sample initially decreased and then stabilised after ten days, with axial strains stabilising four days later. On Day 25, gas pressure was increased to 6 MPa, at which point the downstream pressure suddenly increased to 4.2 MPa. Thereafter, back-pressure decreased steadily without showing any conspicuous sign of stabilising. In parallel, axial and lateral strains increased rapidly and appeared to stabilize by Day 35. This was followed by an acceleration of axial strain up to Day 42. Alongside these accelerating strains, upstream and downstream gas pressures dropped suddenly, which seems to indicate that the sample underwent micro-cracking. These observations show that the onset of gas migration is described by model (iii); corresponding to gas micro-fissuring of the saturated sample. The maximum pressure that was reached seems lower than that conventionally measured, and the micro-fissuring phase corresponds to an acceleration of the axial and lateral strains of the sample until failure. In summary, data from these two experimental studies clearly shows that as gas starts to move through the Callovo-Oxfordian clay-stone, the sample undergoes mechanical dilation. Under in situ conditions, the onset of dilation is a necessary precursor for the advective movement of gas

[en] Research on the effect of temperature changes on the behaviour of geo-materials has become increasingly important in recent years. This growing interest is partially due to the recent development of high-level nuclear waste disposals. Because of the complex influence of temperature in these areas, it is necessary to understand the effects of temperature on rock-like materials and use the appropriate constitutive equations to numerically model these phenomena. In this paper, a thermoplastic/viscoplastic constitutive model is developed for this purpose. The model includes thermal softening, the evolution of the yield functions with temperature, and the effects of temperature on the time-dependent behaviour. The model performance is demonstrated by some simple test cases on Tournemire and Bure clayey rocks including triaxial compression tests and creep tests under constant temperatures. The numerical results are discussed using experimental data, which demonstrate that the model can reproduce the overall behaviour of this type of materials under deviatoric loads and non-isothermal conditions. (authors)

[en] Document available in extended abstract form only. In order to describe rocks behavior with constitutive models able to represent the degradation of the material, a regularization method is used to limit the influence of the spatial discretization. The recent development of the regularization method called the second gradient of dilation in the finite element software Code-Aster (developed by EDF-R and D) allows an objective numerical description of coupled problem for dilating geo-materials in post localized calculations. In the second gradient of dilation method, an additional parameter must be determined with regard to the more classical models. This coefficient sets the thickness of numerical shear bands that appear in post localized states. It also rules the slope of the stress-strain curve which is directly connected to the energy dissipated during the degradation of the material. The aim of the work performed on clays extracted from the EDF site of Sisteron in France was to determine this coefficient for the material taking into account the experimental data available. The idea is to establish a link between the numerical shear bands, which result from the diffusion of the plastic strain in the mesh, and the experimental induced structure that appears for non-zero confining pressures in tri-axial tests. Experimental tri-axial compression tests have been carried out in 2011 by the LaEGO on macroscopic samples (76*38 mm) from the clay of Sisteron. These tests have been achieved for different confining pressures (0, 2, 5 and 10 MPa). The constitutive model used for this approach is the associated Drucker-Prager model with a linear softening evolution. This model was chosen for its simplicity and the small number of parameters governing the slope after the peak strength. Obviously, this model can reproduce only roughly the behavior of the material but the goal is essentially to define a methodology which could be reproduced with more complex models like the L and K model. The methodology followed throughout this work is described in the following. - The first step is the classical approach without regularization method on a material point, in order to settle the numerical constitutive model on experimental results and determine a set of parameters subsequently used as input data for the non-local approach. - Then, a characteristic length (bandwidth) is chosen, according to the size of the sample and the spatial discretization of the mesh. In our case, this length is taken equal to 1 cm with about 6 mesh elements in the bandwidth. - A theoretical indicator is then used to determine an analytical ratio representing the coefficient of regularization (coefficient to determine) out of the characteristic length squared. This theoretical factor is extracted from the resolution of a 1D analytical problem of a dilatant shear band using the tangent stiffness matrix of the problem. Ratios are calculated for different slopes after the peak strength and according to the chosen characteristic length, the coefficient of regularization to use in non-local computations can be deduced. - Non-local computations are conducted with the corresponding values of that coefficient. Numerical results can be confronted to experimental data in the stress-strain curve and shear bands can be observed. The methodology initiated in this work seems to give first good results. It allows for a given material and a given mesh to determine the coefficient of regularization taking into account the behavior of the material considered. However, the methodology used must be reproduced with different slopes and different characteristic lengths to determine which unique couple better fits the experimental data. The prospects for this work concern the transfer of the experience acquired: - on more complex constitutive models (as L and K model for Callovo-Oxfordian clays); - taking into account the non-uniqueness of bifurcated solutions obtained; - to underground applications on the research laboratory of Andra. (authors)

[en] The present work focuses on a new numerical model for the fully coupled hydro-mechanical analysis of groundwater flows through palustric saturated media. In particular, the presence and eventual propagation of fluid-driven fractures is accounted for within a non regularized cohesive zone model. In this paper, the fracture propagation is considered as a reactivation process: the fracture already exists and evolves (i.e. opens or closes) on a pre-defined path initially constrained. The Talon-Curnier constitutive law is considered for the fracture interfaces and its expression has been adapted to the hydro-mechanical coupling related to the fracture evolution. The fluid pressure inside the fracture is governed by the lubrication equation. The momentum-stress balance equations involving fluid flow and deformation of the solid porous matrix are derived within the framework of the generalized Biot theory. The extended finite element method (XFEM) is preferred to a standard finite element spatial discretization in order to easily handle the presence and evolution of discontinuities in the porous medium. A set of four Lagrange multipliers is introduced to prevent spurious oscillations of the numerical solution at the interface. Comparisons between numerical results and theoretical solution assess the validity of the model presented in this paper. In addition, the hydro-mechanical interactions between neighboring fractures and the effects of the permeability of the porous medium are investigated. We also demonstrate the capability of our model to handle non-planar fracture paths. (authors)

[en] This session gathers 30 articles (posters) dealing with: the three Dimensional analyses of combined gas, heat and nuclide transport in a repository considering coupled thermo-hydro geomechanical processes; the experimental study on the thermo-hydro-mechanical behaviour of boom clay; hydraulic in-situ measurements in the Opalinus clay in the frame of a heater test performed at the Mont Terri URL; the hydro-mechanical behaviour of natural boom clay in controlled-suction tests; a constitutive approach to address the thermal and hydric impacts in the concept of deep radioactive waste repositories; the numerical analysis on stability of boom clay tunnel by shield construction; a thermo-hydro-mechanical model for clay in unsaturated conditions; the 3D modelling of TER experiment accounting for fully anisotropic thermo-poro-elastic behaviour; the hydro-mechanical modeling of shaft excavation in Meuse/Haute-Marne laboratory; the modelling of drying damage in engineered and natural clay barriers for nuclear waste disposal; the elasto-viscoplastic behaviour of Meuse/Haute-Marne argillite: laboratory tests and modelling; the long-term behaviour of a lime treated soil under percolation conditions; the stress redistribution and hydro-mechanical effects due to excavation and drilling operations in TER experiment; a thermodynamic model on swelling of bentonite buffer and backfill materials; the 3D analysis of a heating test in the Opalinus clay; the THM analysis of a 'mock-up' laboratory experiment using a double-structure expansive model; the measurement of the effect of re-confinement on rock properties around a slot; a laboratory Study of desaturation - re-saturation effects on a clay-stone; the deformation induced by dissolution of salts in porous media; the bentonite swelling pressure in pure water and saline solutions; the mineralogy and sealing properties of various bentonites and smectite-rich clay materials; the evaluation of the geochemical processes occurring in the Opalinus clay formation subjected to a ventilation test; a Soil structure considerations in description of compacted and natural clay behaviour; the hydro-mechanical behaviour of Tunisian clayey soil used as discharge site of acidic waste; the Consolidation and rebound properties of Opalinus clay: a long-term, fully-drained test; the multidimensional modeling of a poro-elastic medium: identification of the behaviour of a clay formation from a stochastic representation of piezometric fluctuations; various approaches for the comprehension of the time-dependent behaviour of Callovo-Oxfordian argilite; a new approach of estimating the influence of drilling mud on the borehole pressure history; the thermo-chemical-hydro-mechanical modelling: contributions to the assessment of the long term behaviour of a nuclear waste disposal in a deep clay formation; and the impact of thermal load on the far field and galleries of a repository

[en] This document brings together the abstracts of the 39 presentations given at this meeting days on uranium, organized by the French geological society, and dealing with: 1 - Prospective study of the electronuclear technological transition; 2 - The front-end of the nuclear cycle: from the molecule to the process; 3 - Geophysics: recent changes; 4 - Use of well logging in uranium exploration; 5 - Genetical classification of thorium deposits; 6 - Genetical nomenclature of uranium sources; 7 - Uranium deposits linked to a Proterozoic discordance - retrospective; 8 - The use of spectral analysis techniques in uranium exploration: real-time mapping of clay alteration features; 9 - Development of functionalized silk-screened carbon electrodes for the analysis of uranium trace amounts; 10 - Study of the actinides solvation sphere in organic environment; 11 - Thermodynamic of uraniferous phases of interest for the nuclear cycle; 12 - Heap leaching of marginal minerals at Somair: from lab studies to the production of 700 t of uranium/year; 13 - Agglomeration phenomenology and role of iron in uranium heap leaching; 14 - Chloride uranyl complexes up to 300 deg. C along the saturation vapour curve: Raman spectroscopy analysis and metallogenic consequences; 15 - Weathering systems in the Shea Creek deposit (Athabasca, Canada): vertical variability of argillaceous weathering; 16 - Weathering systems in the Shea Creek deposit (Athabasca, Canada): contribution of irradiation defects in clays to the tracing of past uranium migrations; 17 - Uranium concentrations in mineralizing fluids of the Athabasca basin: analytical and experimental approach; 18 - Paleo-surfaces and metallic rooting: the autochthonous uranium of pre-Athabasca paleo-alterites, Canada; 19 - Distribution of argillaceous parageneses in the Imouraren deposit - Niger; 20 - Heat flux and radioelements concentration (U, Th, K) of precambrian basements: implications in terms of crust growth mechanisms, paleo-temperature, and metallogenic provinces; 21 - Magmatic-hydrothermal transition in the Roessing pegmatite: implications for uranium mineralisation; 22 - Deformation and partial fusion of a Archean-paleo-Proterozoic crust: implication on uraniferous ores mobilization and deposition, Torngats orogenesis, Ungava bay; 23 - Black chert pebbles of the Pongola basin conglomerates (∼2, 9 Ga - South Africa): a potential uranium source?; 24 - origin and evolution of detrital pyrites in meso-Archean conglomerates (3.08-2.64 Ga) of South Africa: uranium source or trap?; 25 - Experimental study of U(VI) carbonates with respect to 3 parameters: pH, carbonate concentration, temperature, using vibrational (Raman, FTIR, ATR) and optical (UV-visible) spectroscopy; 26 - Nature and significance of the contact between the Abbabis gneiss complex and the meta-sedimentary sequences of the Damara orogenic belt; 27 - Metallogenic potentialities of Proterozoic orogenic belts accreted to Archean basements: the Damara/Lufilien orogen - Namibia and Zambia; 28 - Contribution of the Geological Exploration to the development of the KATCO ISR mine - Chu-Sarysu basin, Kazakhstan; 29 - Remarks about some remarkable events which occurred during the Francevillien formation; 30 - Geochemical signature of different mineral phases obtained by ICP-MS laser ablation (trace elements and rare earths): Application Uranium deposits; 31 - Role of fluids and irradiation in complex pegmatite euxenite/zircon assemblies from Norway and their U-Pb geochronological consequences; 32 - Mechanical modeling of rupture around metamictic minerals; 33 - Helium diffusion in apatite: Effect alpha recoil-linked damages; 34 - Rare earth spectra in uranium oxides: a marker of the uranium deposit type; 35 - Rare earths: tracers of uranium behaviour during acid sulphated hydrothermal weathering - the Guadeloupe example; 36 - What metallogenic model for the Kiggavik-Andrew Lake trend? Nunavut, Canada; 37 - Uranium mobility in the Southern Armorican system; 38 - Uranium Clusters: Models for Environmentally Relevant Species; 39 - Uranium speciation in Nopal I opals - Sierra Pena Blanca, Mexico