Search

International audience

Three classes of experiments are considered in this paper to provide information for two artificially prepared Boom clay fabrics: mercury intrusion/extrusion tests; main wetting/drying paths; and water inflow/outflow transient (permeability) tests. These tests, which are usually treated separately, are joined in a common reference frame to provide information about the morphology of the porous medium and factors influencing Boom clay unsaturated hydraulic states with reference to water retention curves and relative water permeability values. The main objective is to interpret mercury intrusion porosimetry results in order to define an entrance pore size region at ca 130 to 180 nm separating intra-aggregate and inter-aggregate zones. This pore size region is further associated to a delimiting zone in the retention curve separating regions of ‘intra-aggregate governing suction’ at gravimetric water contents lower than 13–15% (gravimetric water content is not affected by mechanical effects) and ‘inter-aggregate governing suction’ (gravimetric water content is sensible to mechanical actions). This water content is further used to define a threshold zone around a relative water permeability of kw/kws=0.01 delimiting a zone of greater water relative permeability from others that present a restricted flow in a generalised Darcian sense. All these results are consistent with the existence of two main pore size regions: an intra-aggregate porosity with quasi-immobile water that is little affected by loading processes and an inter-aggregate porosity for which the loading mechanism results in a reduction of interconnected macropores affecting free water. Testing results show that intra-aggregate water represents between 54 and 59% of the total volume of water in soil in a low-porosity packing compacted at a dry unit weight of 16.7 kN m-3, whereas it corresponds to ca 28 and 38% in the case of a high-porosity packing compacted at a dry unit weight of 13.7 kN m-3.

The main purpose of this paper is to analyse the convergence measurements of the ALC1604 in situ heating test carried out in the Callovo-Oxfordian claystone formation (COx) in the Meuse/Haute-Marne underground research laboratory (MHM URL). The concept of the test consists of horizontal micro-tunnel, equipped with a steel casing. The micro-tunnel is excavated in the direction of the horizontal principal major stress (σH). In situ observations showed anisotropic convergence with the maximum and minimum values in the horizontal and vertical directions, respectively. Coupled THM numerical analyses have been carried out to provide a structured framework for interpretation, and to enhance understanding of THM behaviour of Callovo-Oxfordian claystone. However, a special mechanical constitutive law is adopted for the description of the time-dependent anisotropic behaviour of the COx. The simulation of the test using this enhanced model provides a satisfactory reproduction of the THM long-term anisotropic convergence results. It also provides a better understanding of the observed test response.

The paper presents an interpretation of the full-scale ALC1604 in situ heating test carried out in Callovo-Oxfordian claystone (COx) in the Meuse/Haute-Marne underground research laboratory (MHM URL). The MHM URL is a site-specific facility planned to study radioactive waste disposal in the COx. The thermo-hydro-mechanical (THM) behaviour of the host rock is significant for the design of the underground radioactive waste disposal facility and for its long-term safety. When subjected to thermal loading, the Callovo-Oxfordian claystone of low permeability (~10-20-10-21 m2) exhibits a strong pore pressure response that significantly affects the hydraulic and mechanical behaviour of the material. The observations gathered in the in situ test have provided an opportunity to examine the integrated thermo-hydro-mechanical (THM) response of this sedimentary clay. Coupled THM numerical analyses have been carried out to provide a structured framework for interpretation, and to enhance understanding of THM behaviour of COx. Numerical analyses have been based on a coupled theoretical formulation that incorporates a constitutive law specially developed for this type of material. The law includes a number of features that are relevant for a satisfactory description of the hydromechanical behaviour. By performing the numerical analysis, it has been possible to incorporate anisotropy of material parameters and of in situ stresses. The performance and analysis of the in situ tests have significantly enhanced the understanding of a complex THM problem and have proved the capability of the numerical formulation to provide adequate predictive capacity.

International audience; The environmental conditions play an important role in the stability of rock cliffs. In fact, in several cases the weather-induced mechanisms have been considered as the triggering factor of instabilities. Daily and seasonal temperature fluctuations can generate internal stress; high enough to create and propagate cracks in the most superficial zone of rock cliffs. An experimental program has been developed to evaluate the damage induce in a limestone, due to natural thermal cycles. A numerical constitutive model is proposed and implemented in Code_Bright in order to be able to reproduce the observed phenomena .

International audience

International audience; The Callovo-Oxfordian claystone (COx) is considered as a potential geological formation to host an industrial radioactive waste repository in France, thanks to its favorable characteristics for radioactive waste containment, as it has a very low hydraulic conductivity, small molecular diffusion and significant retention capacity for radionuclide. A deep 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. Several constitutive models have been developed/used in the framework of the R&D and simulation programs of Andra. These models aim to reproduce the THM behavior of COx under different repository situations and for different structures. A model benchmark exercise has been launched since 2012 to provide an overall view of the developed models, their basic assumptions, their mathematical descriptions, variables and parameters, and to investigate the consequences of these basic assumptions on the calculations results regarding to the experimental observations. Three main constitutive model families are considered; namely, visco-elasto-plastic models, damagemechanics based and computational homogenized (CHM) ones. Nine teams using different models have been participated to this benchmark exercise.

Boom and Ypresian clays are being studied in Belgium in connection with the design of a repository for radioactive waste. Within this context, thermal impact may play an important role on the behaviour of these low-permeability clays. To evaluate this impact, heating pulse tests on intact borehole samples were carried out using an axi-symmetric and constant volume heating cell with controlled hydraulic boundary conditions. Attention is focused on the time evolution of temperature and pore water pressure changes along heating and cooling paths -i.e., pore pressure build-up during quasi-undrained heating and later dissipation to the applied hydraulic boundary conditions. A coupled thermo-hydro-mechanical finite element program was used in a first stage to determine thermal parameters by back-analysis and then to simulate selected experimental results on Boom clay

Boom Clay is being studied in Belgium in connection with the design of a repository for radioactive waste. Within this context, thermal impact may play an important role on the behaviour of this low-permeability clay. To evaluate this impact, heating pulse tests on intact borehole samples were carried out using an axi-symmetric and constant volume heating cell with controlled hydraulic boundary conditions. Attention is focused on the time evolution of temperature and pore water pressure changes along heating and cooling paths –i.e., pore pressure build-up during quasi-undrained heating and later dissipation to the applied hydraulic boundary conditions–. A coupled thermo-hydro-mechanical finite element program was used in a first stage to determine thermal parameters by back-analysis and then to simulate the experimental results.