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Paul Wersin - One of the best experts on this subject based on the ideXlab platform.
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multicomponent diffusion in a 280 m thick Argillaceous Rock sequence
Applied Geochemistry, 2018Co-Authors: Paul Wersin, Martin Mazurek, Thomas Gimmi, Peter Altepping, Marek Pekala, Daniel TraberAbstract:Abstract Diffusion is the main transport mechanism in many Argillaceous formations. In this study, tracer and ion profiles in a 280 m thick clay-rich sequence were simulated by single component and multicomponent diffusion modelling. Drillcores from this sequence originating from a deep borehole in Schlattingen (NE Switzerland) had been previously extensively analysed in terms of porewater chemistry, mineralogy and diffusion parameters. In particular, data from high-pressure core squeezing had enabled to obtain depth profiles of major solutes and water tracers over the entire sequence. The hydrogeological conditions at the site were constrained in the model by the analogy of the nearby site at Benken. In a first step, a simple single component diffusion (SCD) model was set up to simulate the profiles of conservative tracers (δ2H, δ18O, Cl−), to check reasonable boundary conditions for the adjacent aquifers and to estimate characteristic diffusion times. Based on these findings, a multicomponent diffusion (MCD) model considering explicitly diffusion in the electrical double layer (EDL) and the “free” water and a chemical equilibrium model was used to simulate the diffusion of major cations (Na+, Ca2+, Mg2+, K+, Sr2+) and anions (Cl−, SO42−, HCO3−). The SCD modelling resulted in a good match of the measured water tracer and chloride profiles in spite of the uncertainty in the conditions regarding the surrounding aquifers. Diffusion times of 0.5–1 Ma were deduced which are in the same range as those postulated previously for the Benken site. Using the same type of boundary conditions, a reasonably good fit of the measured major cation and anion data could be obtained with the MCD model. The results were not sensitive to uncertainties inherent in the MCD model, such as the extent of surface charge screening by fixed cations or the thickness of the EDL. This supports the robustness of the model approach as long as key features such as anion exclusion are captured. Overall, the suitability of the MCD model for simulating cation and anion fluxes in Argillaceous Rocks over large distances and long timescales could be established. The results also support the validity of squeezing data from drillcores as proxy for in-situ porewater data.
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constraining porewater chemistry in a 250 m thick Argillaceous Rock sequence
Chemical Geology, 2016Co-Authors: Paul Wersin, Catherine Lerouge, Martin Mazurek, Urs Mader, Thomas Gimmi, Daniel Rufer, Daniel TraberAbstract:The geochemistry of an Argillaceous Rock sequence from a deep borehole in NE-Switzerland was investigated. The focus was to constrain the porewater chemistry in low permeability Jurassic Rocks comprising the Liassic, the Opalinus Clay formation, the „Brown Dogger‟ unit and the Effingen Member (Malm). A multi-method approach including mineralogical analysis, aqueous and Ni-ethylenediamine extraction, squeezing tests and pCO2 measurements as well as geochemical modelling was applied for this purpose. A consistent dataset was obtained with regard to the main solutes in the porewaters. A fairly constant anionaccessible porosity of 50% of the total porosity was deduced for all analysed samples which displayed variable clay-mineral contents. Sulphate concentrations were shown to be constrained by a sulphate-bearing phase, presumably by celestite or a Sr-Ba sulphate. Application of a simple equilibrium model, including cation exchange reactions, calcite and celestite equilibrium showed good agreement with squeezing data, indicating the suitability of the modelling approach to simulate porewater chemistry in the studied Argillaceous Rocks. The modelling highlighted the importance of correct determination of the exchangeable cation population. The analysis corroborates that squeezing of the studied Rocks is a viable and efficient way to sample porewater.
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geochemical modelling of bentonite porewater in high level waste repositories
Journal of Contaminant Hydrology, 2003Co-Authors: Paul WersinAbstract:The description of the geochemical properties of the bentonite backfill that serves as engineered barrier for nuclear repositories is a central issue for performance assessment since these play a large role in determining the fate of contaminants released from the waste. In this study the porewater chemistry of bentonite was assessed with a thermodynamic modelling approach that includes ion exchange, surface complexation and mineral equilibrium reactions. The focus was to identify the geochemical reactions controlling the major ion chemistry and acid-base properties and to explore parameter uncertainties specifically at high compaction degrees. First, the adequacy of the approach was tested with two distinct surface complexation models by describing recent experimental data performed at highly varying solid/liquid ratios and ionic strengths. The results indicate adequate prediction of the entire experimental data set. Second, the modelling was extended to repository conditions, taking as an example the current Swiss concept for high-level waste where the compacted bentonite backfill is surrounded by Argillaceous Rock. The main reactions controlling major ion chemistry were found to be calcite equilibrium and concurrent Na-Ca exchange reactions and de-protonation of functional surface groups. Third, a sensitivity analysis of the main model parameters was performed. The results thereof indicate a remarkable robustness of the model with regard to parameter uncertainties. The bentonite system is characterised by a large acid-base buffering capacity which leads to stable pH-conditions. The uncertainty in pH was found to be mainly induced by the pCO(2) of the surrounding host Rock. The results of a simple diffusion-reaction model indicate only minor changes of porewater composition with time, which is primarily due to the geochemical similarities of the bentonite and the Argillaceous host Rock. Overall, the results show the usefulness of simple thermodynamic models to describe porewater chemistry of expandable clays although significant uncertainties with regard to the effects of swelling and physico-chemical properties of the interstitial water remain.
Antonio Gens Sole - One of the best experts on this subject based on the ideXlab platform.
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elastoplastic modelling of a ventilation test in Argillaceous Rock
COMPLAS XIII : proceedings of the XIII International Conference on Computational Plasticity : fundamentals and applications, 2015Co-Authors: Benoit Garitte, Antonio Gens SoleAbstract:A full scale ventilation field test has been performed in a 10 m section of a 1.3m diameter unlined tunnel excavated in the Mont Terri underground laboratory. The tunnel has been excavated in Opalinus clay, a stiff strongly-bedded overconsolidated clay of Middle Jurassic age found in the Jura Mountains of Northern Switzerland. The test involved several stages of wetting and drying under controlled conditions and was fully instrumented with pore pressure, relative humidity and displacement sensors [1]. Coupled hydromechanical analyses have been performed taking into account the specific features of the test, especially the vapour migration phenomena and the conditions in the boundary between air and clay. The mechanical behaviour of the Opalinus clay has been simulated by an elastoplastic model in order to capture the potential irreversibility of deformations caused by ventilation. The results of the calculations match quite closely the field test observations such as the existence of two different zones around the tunnel: a desaturation zone reaching only about 50 cm inside the clay and a larger zone, extending 2.5-3m from the tunnel wall, in which the Opalinus clay is under suction. Also, displacements close to the tunnel follow closely the changes of the relative humidity of the air in the tunnel; it compresses when ventilation involves dry air and it exhibits extension when wetting occurs. Although displacements are modest, it can be observed that the net effect of the full ventilation history is a net compression indicating a degree of irreversibility in the clay behaviour. Such irreversibility is well reproduced by the elasto-plastic coupled analysis (see Figure).
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anisotropic failure criterion for an Argillaceous Rock formulation and application to an underground excavation case
COMPLAS XIII : proceedings of the XIII International Conference on Computational Plasticity : fundamentals and applications, 2015Co-Authors: Miguel A Manica, Antonio Gens Sole, Jean Vaunat, Daniel RuizAbstract:Because of their limited strength, an important issue in underground excavations in Argillaceous Rocks is the generation of a damaged zone around the cavity caused by the process of excavation itself. Field observations show that often the extent and features of the damaged zone are affected by the anisotropic nature of the material concerning especially the failure conditions of the Rock. This is especially apparent in cases where the in situ stress is quasi-isotropic where the non-uniform configuration of the damaged zone can only be ascribed to the anisotropic properties of the material. In this contribution, a cross-anisotropic extension of an elastoplastic constitutive model is described, based on a non-uniform scaling of the stress tensor. The Mohr-Coulomb yield condition is employed, although this concept can be applied to any other stress-based criterion. It has as main advantage the possibility of being incorporated into an already implemented constitutive model with only minor modifications. The resulting constitutive model has been applied to the coupled hydromechanical simulation of an excavation of a horizontal tunnel in the underground research laboratory at Bure (France). The orientation of the tunnel ensures that the transverse in situ stress state is nearly isotropic. The tunnel excavation has been intensely monitored and the nature and extension of the damaged zone have been studied by a variety of field techniques. As the Figure shows, the analysis performed using the elastoplastic model incorporating the anisotropic failure criterion is able to reproduce the observed geometry of the damaged zone. The anisotropy of convergence measurements is also matched satisfactorily. a) b) Excavation damaged zone a) Observed [1] b) Computed REFERENCES [1] G. Armand, F. Leveau, C. Nussbaum, R. de La Vaissiere, A. Noiret, D. Jaeggi, P. Landrein, C. Righini,. “Geometry and properties of the excavation-induced fractures at the Meuse/Haute- Marne URL drifts”, Rock Mechanics and Rock Engineering, 47, 21-4 (2014). .
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thermo hydro mechanical response of an Argillaceous Rock experimental results and modelling
X International Conference on Computational Plasticity, 2009Co-Authors: Benoit Garitte, Jean Vaunat, Antonio Gens SoleAbstract:B. Garitte*, Jean Vaunat† and Antonio Gens† * International Center for Numerical Methods in Engineering (CIMNE) Universidad Politecnica de Cataluna Campus Norte UPC, 08034 Barcelona, Spain e-mail: benoit.garitte@upc.edu † Department of Geotechnical Engineering and Geosciences Universidad Politecnica de Cataluna Campus Norte UPC, 08034 Barcelona, Spain email: jean.vaunat@upc.edu email : antonio.gens@upc.edu
Benoit Garitte - One of the best experts on this subject based on the ideXlab platform.
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elastoplastic modelling of a ventilation test in Argillaceous Rock
COMPLAS XIII : proceedings of the XIII International Conference on Computational Plasticity : fundamentals and applications, 2015Co-Authors: Benoit Garitte, Antonio Gens SoleAbstract:A full scale ventilation field test has been performed in a 10 m section of a 1.3m diameter unlined tunnel excavated in the Mont Terri underground laboratory. The tunnel has been excavated in Opalinus clay, a stiff strongly-bedded overconsolidated clay of Middle Jurassic age found in the Jura Mountains of Northern Switzerland. The test involved several stages of wetting and drying under controlled conditions and was fully instrumented with pore pressure, relative humidity and displacement sensors [1]. Coupled hydromechanical analyses have been performed taking into account the specific features of the test, especially the vapour migration phenomena and the conditions in the boundary between air and clay. The mechanical behaviour of the Opalinus clay has been simulated by an elastoplastic model in order to capture the potential irreversibility of deformations caused by ventilation. The results of the calculations match quite closely the field test observations such as the existence of two different zones around the tunnel: a desaturation zone reaching only about 50 cm inside the clay and a larger zone, extending 2.5-3m from the tunnel wall, in which the Opalinus clay is under suction. Also, displacements close to the tunnel follow closely the changes of the relative humidity of the air in the tunnel; it compresses when ventilation involves dry air and it exhibits extension when wetting occurs. Although displacements are modest, it can be observed that the net effect of the full ventilation history is a net compression indicating a degree of irreversibility in the clay behaviour. Such irreversibility is well reproduced by the elasto-plastic coupled analysis (see Figure).
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Accounting for anisotropic effects in the prediction of the hydro-mechanical response of a ventilated tunnel in an Argillaceous Rock
Journal of Rock Mechanics and Geotechnical Engineering, 2013Co-Authors: Alain Millard, Alex Bond, Shigeo Nakama, Chengyuan Zhang, Jean-dominique Barnichon, Benoit GaritteAbstract:In order to investigate the hydro-mechanical (HM) and chemical perturbations induced in an Argillaceous formation by forced ventilation during the operational period of a nuclear waste repository, a specific experiment has been performed in a tunnel, at Mont Terri Underground Research Laboratory (URL) in Switzerland. This experiment has been selected in the international project DECOVALEX for model validation and the numerical simulation of this ventilation experiment (VE) is the object of the present paper. Since the Argillaceous Rock exhibits anisotropic properties, particular attention is given to the evaluation of the effects of various anisotropic features on the predicted results. In situ measurements such as relative humidity (RH), global water mass extracted, pore water pressure, water content, and relative displacements are compared to predictions using both isotropic and anisotropic parameters. Water permeability anisotropy is shown to be the most influencing parameter by far, whereas in situ stress anisotropy has an effect only during the excavation phase. The anisotropy for mechanical parameterization has also some influence, in particular through HM couplings. These HM couplings have the potential to be very significant in terms of providing confidence in describing the experimental observation, and should be considered for further investigation.
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thermo hydro mechanical response of an Argillaceous Rock experimental results and modelling
X International Conference on Computational Plasticity, 2009Co-Authors: Benoit Garitte, Jean Vaunat, Antonio Gens SoleAbstract:B. Garitte*, Jean Vaunat† and Antonio Gens† * International Center for Numerical Methods in Engineering (CIMNE) Universidad Politecnica de Cataluna Campus Norte UPC, 08034 Barcelona, Spain e-mail: benoit.garitte@upc.edu † Department of Geotechnical Engineering and Geosciences Universidad Politecnica de Cataluna Campus Norte UPC, 08034 Barcelona, Spain email: jean.vaunat@upc.edu email : antonio.gens@upc.edu
Daniel Traber - One of the best experts on this subject based on the ideXlab platform.
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multicomponent diffusion in a 280 m thick Argillaceous Rock sequence
Applied Geochemistry, 2018Co-Authors: Paul Wersin, Martin Mazurek, Thomas Gimmi, Peter Altepping, Marek Pekala, Daniel TraberAbstract:Abstract Diffusion is the main transport mechanism in many Argillaceous formations. In this study, tracer and ion profiles in a 280 m thick clay-rich sequence were simulated by single component and multicomponent diffusion modelling. Drillcores from this sequence originating from a deep borehole in Schlattingen (NE Switzerland) had been previously extensively analysed in terms of porewater chemistry, mineralogy and diffusion parameters. In particular, data from high-pressure core squeezing had enabled to obtain depth profiles of major solutes and water tracers over the entire sequence. The hydrogeological conditions at the site were constrained in the model by the analogy of the nearby site at Benken. In a first step, a simple single component diffusion (SCD) model was set up to simulate the profiles of conservative tracers (δ2H, δ18O, Cl−), to check reasonable boundary conditions for the adjacent aquifers and to estimate characteristic diffusion times. Based on these findings, a multicomponent diffusion (MCD) model considering explicitly diffusion in the electrical double layer (EDL) and the “free” water and a chemical equilibrium model was used to simulate the diffusion of major cations (Na+, Ca2+, Mg2+, K+, Sr2+) and anions (Cl−, SO42−, HCO3−). The SCD modelling resulted in a good match of the measured water tracer and chloride profiles in spite of the uncertainty in the conditions regarding the surrounding aquifers. Diffusion times of 0.5–1 Ma were deduced which are in the same range as those postulated previously for the Benken site. Using the same type of boundary conditions, a reasonably good fit of the measured major cation and anion data could be obtained with the MCD model. The results were not sensitive to uncertainties inherent in the MCD model, such as the extent of surface charge screening by fixed cations or the thickness of the EDL. This supports the robustness of the model approach as long as key features such as anion exclusion are captured. Overall, the suitability of the MCD model for simulating cation and anion fluxes in Argillaceous Rocks over large distances and long timescales could be established. The results also support the validity of squeezing data from drillcores as proxy for in-situ porewater data.
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constraining porewater chemistry in a 250 m thick Argillaceous Rock sequence
Chemical Geology, 2016Co-Authors: Paul Wersin, Catherine Lerouge, Martin Mazurek, Urs Mader, Thomas Gimmi, Daniel Rufer, Daniel TraberAbstract:The geochemistry of an Argillaceous Rock sequence from a deep borehole in NE-Switzerland was investigated. The focus was to constrain the porewater chemistry in low permeability Jurassic Rocks comprising the Liassic, the Opalinus Clay formation, the „Brown Dogger‟ unit and the Effingen Member (Malm). A multi-method approach including mineralogical analysis, aqueous and Ni-ethylenediamine extraction, squeezing tests and pCO2 measurements as well as geochemical modelling was applied for this purpose. A consistent dataset was obtained with regard to the main solutes in the porewaters. A fairly constant anionaccessible porosity of 50% of the total porosity was deduced for all analysed samples which displayed variable clay-mineral contents. Sulphate concentrations were shown to be constrained by a sulphate-bearing phase, presumably by celestite or a Sr-Ba sulphate. Application of a simple equilibrium model, including cation exchange reactions, calcite and celestite equilibrium showed good agreement with squeezing data, indicating the suitability of the modelling approach to simulate porewater chemistry in the studied Argillaceous Rocks. The modelling highlighted the importance of correct determination of the exchangeable cation population. The analysis corroborates that squeezing of the studied Rocks is a viable and efficient way to sample porewater.
Thomas Gimmi - One of the best experts on this subject based on the ideXlab platform.
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multicomponent diffusion in a 280 m thick Argillaceous Rock sequence
Applied Geochemistry, 2018Co-Authors: Paul Wersin, Martin Mazurek, Thomas Gimmi, Peter Altepping, Marek Pekala, Daniel TraberAbstract:Abstract Diffusion is the main transport mechanism in many Argillaceous formations. In this study, tracer and ion profiles in a 280 m thick clay-rich sequence were simulated by single component and multicomponent diffusion modelling. Drillcores from this sequence originating from a deep borehole in Schlattingen (NE Switzerland) had been previously extensively analysed in terms of porewater chemistry, mineralogy and diffusion parameters. In particular, data from high-pressure core squeezing had enabled to obtain depth profiles of major solutes and water tracers over the entire sequence. The hydrogeological conditions at the site were constrained in the model by the analogy of the nearby site at Benken. In a first step, a simple single component diffusion (SCD) model was set up to simulate the profiles of conservative tracers (δ2H, δ18O, Cl−), to check reasonable boundary conditions for the adjacent aquifers and to estimate characteristic diffusion times. Based on these findings, a multicomponent diffusion (MCD) model considering explicitly diffusion in the electrical double layer (EDL) and the “free” water and a chemical equilibrium model was used to simulate the diffusion of major cations (Na+, Ca2+, Mg2+, K+, Sr2+) and anions (Cl−, SO42−, HCO3−). The SCD modelling resulted in a good match of the measured water tracer and chloride profiles in spite of the uncertainty in the conditions regarding the surrounding aquifers. Diffusion times of 0.5–1 Ma were deduced which are in the same range as those postulated previously for the Benken site. Using the same type of boundary conditions, a reasonably good fit of the measured major cation and anion data could be obtained with the MCD model. The results were not sensitive to uncertainties inherent in the MCD model, such as the extent of surface charge screening by fixed cations or the thickness of the EDL. This supports the robustness of the model approach as long as key features such as anion exclusion are captured. Overall, the suitability of the MCD model for simulating cation and anion fluxes in Argillaceous Rocks over large distances and long timescales could be established. The results also support the validity of squeezing data from drillcores as proxy for in-situ porewater data.
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constraining porewater chemistry in a 250 m thick Argillaceous Rock sequence
Chemical Geology, 2016Co-Authors: Paul Wersin, Catherine Lerouge, Martin Mazurek, Urs Mader, Thomas Gimmi, Daniel Rufer, Daniel TraberAbstract:The geochemistry of an Argillaceous Rock sequence from a deep borehole in NE-Switzerland was investigated. The focus was to constrain the porewater chemistry in low permeability Jurassic Rocks comprising the Liassic, the Opalinus Clay formation, the „Brown Dogger‟ unit and the Effingen Member (Malm). A multi-method approach including mineralogical analysis, aqueous and Ni-ethylenediamine extraction, squeezing tests and pCO2 measurements as well as geochemical modelling was applied for this purpose. A consistent dataset was obtained with regard to the main solutes in the porewaters. A fairly constant anionaccessible porosity of 50% of the total porosity was deduced for all analysed samples which displayed variable clay-mineral contents. Sulphate concentrations were shown to be constrained by a sulphate-bearing phase, presumably by celestite or a Sr-Ba sulphate. Application of a simple equilibrium model, including cation exchange reactions, calcite and celestite equilibrium showed good agreement with squeezing data, indicating the suitability of the modelling approach to simulate porewater chemistry in the studied Argillaceous Rocks. The modelling highlighted the importance of correct determination of the exchangeable cation population. The analysis corroborates that squeezing of the studied Rocks is a viable and efficient way to sample porewater.