Statistical analyses of pressure signals, hydrogeologic characterization and evolution of Excavation Damaged Zone (claystone sites of Mont Terri and Tournemire)

We present statistical analyses of pore pressure and other signals, aimed at characterizing the properties of a geologic porous medium and, particularly, of the Excavation Damaged Zone ("EDZ") around underground galleries. The purpose is not only to identify the material properties, but also to quantify their evolution during excavation (creation of an EDZ). The methods are applied to two Underground Research Laboratories ("URL’s") in claystone sites: Mont Terri in Switzerland (gallery Ga98) and Tournemire in France (gallery Ga03). This work is part of the LP 14 experiment, an international research program of the Mont Terri Consortium, aimed at assessing the isolation properties of claystone as a potential geologic repository for radioactive waste (LP 14 experiment: Long term Pressure experiment, phase 14)

Salt precipitation and trapped liquid cavitation in micrometric capillary tubes.

International audienceLaboratory evidence shows that the occurrence of solid salt in soil pores causes drastic changes in the topology of the porous spaces and possibly also in the properties of the occluded liquid. Observations were made on NaCl precipitation in micrometric cylindrical capillary tubes, filled with a 5.5 M NaCl aqueous solution and submitted to drying conditions. Solid plug-shaped NaCl (halite) commonly grows at the two liquid-air interfaces, isolating the inner liquid column. The initially homogeneous porosity of the capillary tube becomes heterogeneous because of these two NaCl plugs, apparently closing the micro-system on itself. After three months, we observed cavitation of a vapor bubble in the liquid behind the NaCl plugs. This event demonstrates that the occluded liquid underwent a metastable superheated state, controlled by the capillary state of thin capillary films persisting around the NaCl precipitates. These observations show, first, that salt precipitation can create a heterogeneous porous medium in an initially regular network, thus changing the transfer properties due to isolating significant micro-volumes of liquid. Second, our experiment illustrates that the secondary salt growth drastically modifies the thermo-chemical properties of the occluded liquid and thus its reactive behavior

Statistical Analyses of Pore Pressure Signals in Claystone During Excavation Works at the Mont Terri Underground Research Laboratory

In many countries (such as Belgium, Germany, France, Japan, Switzerland, and United Kingdom), deep argillaceous formations are considered as potential host rocks for geological disposal of high-level and intermediate-level long-lived radioactive wastes. Some of these countries are investigating the suitability of high compacted clay-rich rocks at depths down to around 500 m below the ground surface. The general disposal concept comprises a network of drifts and tunnels linked to the surface by shafts and ramps, all artificially ventilated. Research is ongoing in Underground Research Laboratories, like the Mont Terri site in the Swiss Jura, to assess and ensure the safety of the repositories for the full decay life of the radioactive waste, i.e. the capacity of the hypothetical repository toprevent the migration of radionuclides towards the biosphere.[...

In-Pore stress by drying-induced capillary bridges inside porous materials.

International audienceWe present here some evidences that capillary liquid bridges are able to deform micrometric cylindrical pores by tensile stress. Brine-soaked filter membranes are submitted to drying conditions leading to NaCl precipitation inside the 5-10 μm pores. A close examination demonstrated that two forms of NaCl crystallites are successively generated. First, primary cubic crystals grow, driven by the permanent evaporation. When this angular primary solid gets near the pore wall, while the evaporation makes the pore volume to be partly invaded by air, capillary liquid can bridge the nowsmall gap between the halite angles and the pore wall. In a second step, these small capillary bridges are frozen by a secondary precipitation event of concave-shaped NaCl. The proposed interpretation is that the liquid capillary bridges deform the host matrix of the membrane, and the situation is fossilized by the growth of solid capillary bridges. A quantitative interpretation is proposed and the consequences towards the natural media outlined

Bayesian inversion of a chloride profile obtained in the hydraulically undisturbed Opalinus Clay: mass transport and paleo-hydrological implications.

International audienceThe BDB-1 deep inclined borehole was drilled at the Mont Terri rock laboratory (Switzerland) and enabled to acquire elevant data on porewater composition through the Opalinus Clay (OPA) and its bounding formations. Petrophysical measurements were carried out and included water content, water accessible porosity and grain density determination. Conservative anion profiles were obtained by aqueous leaching and out diffusion experiments performed on drillcore samples, and revealed to be consistent with previous studies carried out at the rock laboratory level. Diffusive properties were also investigated using three experimental setups: cubic out diffusion, radial diffusion and through diffusion. These transport parameters were used as a priori values in a Bayesian inversion using a Markov Chain Monte Carlo method to interpret the chloride profile in the Opalinus Clay. Based on a Peclet number analysis using the transport parameters formerly acquired, a purely diffusive scenario enabled specifying the paleohydrogeological evolution of the Mont Terri site from the folding and thrusting of the Jura Mountains to present time and transport parameters

Hydrochimie et geochimie isotopique des saumures petrolieres du Trias et du Dogger dans le bassin de Paris

CNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Origin of Cl− and High δ37Cl Values in Radiocarbon Dated-Fracture Groundwaters at the Tournemire URL (France)

International audienc