Reactive and non-reactive transport modelling in partially water saturated argillaceous porous media around the ventilation experiment,Mont Terri

At Mont Terri Underground Research Laboratory （URL） Switzerland, a specific experiment has been per- formed in a tunnel, in order to investigate the hydro-mechano-chemical （HMC） perturbations induced in the argillaceous formation by forced ventilation. This experiment has been selected in the international project DECOVALEX to be used for process model development and validation. The numerical simula- tion of the geochemical response to the ventilation experiment （VE） is the object of the present paper, focusing on the transport of chloride as a conservative species and sulphate as a reactive species. Uti- lising the validated hydro-mechanical （HM） results from earlier steps of the DECOVALEX task, reactive and non-reactive transport models, incorporating the current understanding of the geochemistry at the site, were successfully constructed for the whole experimental period. The associated parametric and process uncertainty analyses clearly demonstrate that the basic HM understanding must be sound. How- ever, to demonstrate this degree of robustness, the explicit inclusion of process representations of water desaturation, liquid vaporisation, species exclusion porosity, and redox processes, is required.

Approaches for representing hydro-mechanical coupling between sub-surface excavations and argillaceous porous media at the ventilation experiment, Mont Terri

At the Mont Terri Underground Research Laboratory （Switzerland）, a field-scale investigation has been conducted in order to investigate the hydro-mechanical and chemical perturbations induced in the argilla- ceous formation by forced ventilation through a tunnel. This experiment has been selected to be used for processing model development and validation in the international project DECOVALEX-2011. The con- ceptual and mathematical representation of the engineered void, which itself forms a major part of the experiment and is not simply a boundary condition, is the subject of this paper. A variety of approaches have been examined by the contributors to DECOVALEX and a summary of their findings is presented here. Two major aspects are discussed. Firstly, the approaches for the treatment of the surface condition at the porous media/tunnel interface are examined, with two equivalent but differing formulations successfully demonstrated. Secondly, approaches for representing the tunnel with associated air and water vapour movement, when coupled with the hydro-mechanical （HM） representation of the porous medium, are also examined. It is clearly demonstrated that, for the experimental conditions of the ventilation experiment （VE） that abstracted physical and empirical models of the tunnel, can be used successfully to represent the hydraulic behaviour of the tunnel and the hydraulic interaction between the tunnel and the surrounding rock mass.

A diagnostic experiment of the influence of CO_2on winter wheat

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Accounting for anisotropic effects in the prediction of the hydro-mechanical response of a ventilated tunnel in an argillaceous rock

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 vali- dation 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 displace- ments 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.

Analysis of hydro-mechanical processes in a ventilated tunnel in an argillaceous rock on the basis of different modelling approaches

In this paper, a modelling benchmark exercise from the DECOVALEX-2011 project is presented. The bench- mark is based on the performance and results of a laboratory drying test and of the ventilation experiment （VE） carried out in the Mont Terri Underground Rock Laboratory （URL）. Both tests involve Opalinus clay. The work aims at the identification, understanding and quantification of mechanisms taking place during the ventilation of a gallery in argillaceous host rocks on one hand and at investigating the capacity of different codes and individuals to reproduce these processes on the other hand. The 4-year in situ VE took place in a 1.3 m diameter unlined tunnel and included two resaturation-desaturation cycles. The test area was equipped with over one hundred sensors （including the global water mass balance of the system, relative humidity （RH）, water content, liquid pressure, relative displacement and concentration of some chemical species） to monitor the rock behaviour during ventilation. The laboratory drying experiment, carried out before the VE, was designed to mimic the in situ conditions. The work was organized in a progressive manner in terms of complexity of the computations to be performed, geared towards the full hydro-mechano-chemical （HMC） understanding of the VE, the final objective. The main results from the modelling work reported herein are that the response of the host rock to ventilation in argillaceous rocks is mainly governed by hydraulic processes （advective Darcy flow and non-advective vapour diffu- sion） and that the hydro-mechanical （TM） back coupling is weak. A ventilation experiment may thus be regarded as a large scale-long time pump test and it is used to determine the hydraulic conductivity of the rock mass.

A thermo-hydro-mechano-chemical formulation for modeling water transport around a ventilated tunnel in an argillaceous rock

Argillaceous rocks are being considered as potential host rocks for deep geological disposal. For the research work in DECOVALEX-2011, 5 participant research teams performed simulations of a labora- tory drying test and a ventilation experiment for Mont Terri underground laboratory built in argillaceous rock formation. Our study starts with establishing a coupled thermo-hydro-mechano-chemical （THMC） processes model to simulate water transport in rock around the ventilated tunnel. Especially in this THMC formulation, a three-phase and two-constituent hydraulic model is introduced to simulate the processes which occur during tunnel ventilation, including desaturation/resaturation in the rock, phase change and air/rock interface, and to explore the Opalinus clay parameter set, It can be found that water content evolution is very sensitive to intrinsic permeability, relative permeability and capillary pressure in clay rock. Water loss from surrounding rock is sensitive to the change of permeability in clay which is induced by excavation damaged zone. Chemical solute transport in the rock near ventilation experiment tunnel is simulated based on the coupled THMC formulation. It can be estimated that chemical osmotic flow has little significance on water flow modeling. Comparisons between simulation results from 5 teams and experimental observations show good agreement. It increases the confidence in modeling and indi- cates that it is a good start for fully THMC understanding of the moisture transportation and mechanical behavior in argillaceous rock.