Andra performs a wide range of in-situ experiments at its Meuse/Haute-Marne Underground Research Laboratory (MHM URL). The purpose of these experiments is to study the feasibility of a radioactive ...waste repository in the Callovo-Oxfordian claystone formation (COx). An important research program has been conducted by Andra since 2005 to investigate THM response of the COx to a thermal load through laboratory and in situ experimentations. A step-by-step approach is followed, which starts with small scale heating boreholes (TED experiment) and extends to full-scale (ALC experiment). Modelling and interpretation of the TED and ALC experiments are conducted in the context of the Task E within the DECOVALEX-2019 framework. DECOVALEX-2019 is a multidisciplinary, co-operative international research effort focused on modelling coupled Thermal-Hydraulic-Mechanical-Chemical (THMC) processes. Based on the TED experiment measurements, the THM parameters of the COx are calibrated through a fully-coupled THM model using COMSOL. Then, the ALC experiment is successfully blind predicted and interpretatively modelled using the calibrated THM parameters of the COx and the proposed coupled THM model.
Background
To minimize measurement uncertainties and create seamless procedures between tests and simulations for the characterization and prediction of damage in large scale structures, a system ...capable of monitoring the quantities of interest at different scales throughout the test is required.
Objective
The aim of this work is to develop a multiview DIC framework at varying scales in which kinematic fields are expressed on a
unique
mesh.
Methods
A three-point flexural test was performed on a concrete beam and the images acquired by three different cameras were used to perform DIC calculations.
Results
Displacement and strain fields were measured using mono and multiview implementations; their associated uncertainties were assessed. Damage initiation and growth within the sample was quantified based on the standard displacement uncertainty.
Conclusion
The reported results show that the proposed method reduced the associated displacement uncertainties. The onset and propagation of damage was successfully quantified.
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.
Usually, the vulnerability of structures is treated considering only one single hazard, for example either seismic hazard or ground instability. However, historical monuments, cultural heritage ...structures or old masonry structures can be affected, over the past centuries of existence, by a succession of different hazards. The objective of this paper was to quantify the changes in the seismic vulnerability of a given structure previously damaged by quasi-static differential settlements. In view of this, a soil-structure model of the masonry building is constructed using TREMURI software by putting springs at the base of the building to account for the soil behaviour. Classical empirical relationships are used for setting the mechanical properties of these foundation springs. The chosen equations are valid for both static and dynamic situations. The soil-structure model is first submitted to differential settlements with maximum magnitudes ranging from 5 to 25 cm. Then, the damaged structures are submitted to a set of time-histories. Fragility curves taking into consideration permanent differential settlements are finally obtained, using a modified regression technique accounting for the presence of residual drift due to the prior static loading.
The work presented herein aims at characterizing and modeling fracturing (i.e., initiation and propagation of cracks) in a clay-rich rock. The analysis is based on two experimental campaigns. The ...first one relies on a probabilistic analysis of crack initiation considering Brazilian and three-point flexural tests. The second one involves digital image correlation to characterize crack propagation. A nonlocal damage model based on stress regularization is used for the simulations. Two thresholds both based on regularized stress fields are considered. They are determined from the experimental campaigns performed on Lower Watrous rock. The results obtained with the proposed approach are favorably compared with the experimental results.
Sedimentary geomaterials such as rocks frequently exhibit cross-anisotropic properties and their behaviour depends on the direction of loading with respect to their microstructure. As far as material ...rupture is concerned, localised deformation in shear band mode appears generally before cracks and material failure. The influence of cross-anisotropy on the shear strain localisation remains an important issue and is investigated in the present study. To do so, a constitutive elastoplastic cross-anisotropic model that includes anisotropy both on the elastic and plastic characteristics is defined. For the plastic part of the model, the anisotropy of a strength parameter is introduced with a microstructure fabric tensor. Then, the fractures are modelled with finite element methods by considering the development of shear strain localisation bands and an enriched model is used to properly reproduce the shear banding. The cross-anisotropy influence on shear banding is studied through numerical applications of small and large-scale geotechnical problems that engender fractures. The two considered applications are a plane-strain biaxial compression test and an underground gallery excavation. The numerical results provide information about the influence of cross-anisotropy on the appearance and development of shear bands. It has been noticed, among other observations, that the material strength vary with the loading direction and that the development and the shape of the excavation fractured zone that develops around a gallery is strongly influenced by the material anisotropy.
A poromechanical model is developed to identify how chemical reactions of carbonation may impact the mechanical behaviour of wellbore cement in the context of CO
2 storage. The model enables the ...evaluation of pore overpressure, porosity and solid-skeleton strain evolutions during the carbonation process. The major chemical reactions occurring within cement and their consequences on the volumes of dissolved cement matrix and precipitated carbonate are identified. This information is imported into a poromechanical model and the risk of damage is estimated through the calculation of the free energy stored within the solid matrix. A semi-analytical solution is proposed and applied to a simplified 1D cement carbonation example. The risk of damage of the cement structure submitted to intrusion of aqueous CO
2 is estimated. A set of parametric studies is carried out to investigate the effect of medium permeability and effective diffusion coefficient on the damage risk.
Since 2000, the French National Radioactive Waste Management Agency （ANDRA） has been constructing an Underground Research Laboratory （URL） at Bure （east of the Paris Basin） to perform experiments in ...order to obtain in situ data necessary to demonstrate the feasibility of geological repository in the Callovo- Oxfordian claystone. An important experimental program is planned to characterize the response of the rock to different drift construction methods, Before 2008, at the main level of the laboratory, most of the drifts were excavated using pneumatic hammer and supported with rock bolts, sliding steel arches and fiber shotcrete. Other techniques, such as road header techniques, stiff and flexible supports, have also been used to characterize their impacts. The drift network is developed following the in situ major stresses. The parallel drifts are separated enough so as they can be considered independently when their hydromechanical （HM） behaviors are compared. Mine-by experiments have been performed to measure the HM response of the rock and the mechanical loading applied to the support system due to the digging and after excavation. Drifts exhibit extensional （mode I） and shear fractures （modes II and III） induced by excavation works. The extent of the induced fracture networks depends on the drift orientation versus the in situ stress field. This paper describes the drift convergence and deformation in the surrounding rock walls as function of time and the impact of different support methods on the rock mass behavior. An observation based method is finally applied to distinguish the instantaneous and time-dependent parts of the rock mass deformation around the drifts.
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