The Swiss program for the deep-geological disposal of radioactive waste: Status of site selection and concept demonstration

Peer Reviewe

Numerical Implementation of a Critical State Model for Soft Rocks

This paper details the basic tasks for the numerical implementation of a simple elasto-plastic critical state model for bonded materials (i.e. soft rocks-hard soils) into the finite element program SNAC developed at the University of Newcastle in Australia. The first task described focusses on the derivation of the incremental constitutive relationships used to represent the mechanical response of a bonded/cemented material under saturated conditions. The second task presents how these stress-strain relations can be numerically integrated using an explicit substepping scheme with automatic error control. The third task concentrates on the verification of the substepping algorithm proposed. The model used to represent the saturated mechanical response of a bonded material combines the modified Cam clay with the constitutive relationships for cemented materials proposed in Gens & Nova (1993), but incorporates some flexibility on the degradation law adopted. The role of suction and other relevant aspects of unsaturated behaviour are also discussed at the end of the paper

Performance of the Opalinus Clay under thermal loading: experimental results from Mont Terri rock laboratory (Switzerland)

The final publication is available at Springer via http://dx.doi.org/10.1007/s00015-016-0258-8The paper presents an overview of the behaviour of Opalinus Clay under thermal loading as observed in three in situ heating tests performed in the Mont Terri rock laboratory: HE-B, HE-D and HE-E. The three tests are summarily described; they encompass a broad range of test layouts and experimental conditions. Afterwards, the following topics are examined: determination of thermal conductivity, thermally-induced pore pressure generation and thermally-induced mechanical effects. The mechanisms underlying pore pressure generation and dissipation are discussed in detail and the relationship between rock damage and thermal loading is examined using an additional in situ test: SE-H. The paper concludes with an evaluation of the various thermo-hydro-mechanical (THM) interactions identified in the heating tests.Peer ReviewedPostprint (author's final draft

Thermal conductivity of argillaceous rocks: determination methodology using in situ heating tests

This study focuses on the characterisation of thermal conductivity for three potential host rocks for radioactive waste disposal. First, the heat conduction process is reviewed on the basis of an analytical solution and key aspects related to anisotropic conduction are discussed. Then the existing information on the three rocks is summarised and a broad uncertainty range of thermal conductivity is estimated based on the mineralogical composition. Procedures to backanalyse the thermal conductivity on the basis of in situ heating tests are assessed and a methodology is put forward. Finally, this methodology is used to estimate the impact of experimental uncertainties and applied to the four in situ heating tests. In the three potential host rocks, a clear influence of the bedding planes was identified and anisotropic heat conduction was shown to be necessary to interpret the observed temperature field. Experimental uncertainties were also shown to induce a larger uncertainty on the anisotropy ratio than on the equivalent thermal conductivity defined as the geometric mean of the thermal conductivity in the three principal directions

Thermo-hydro-mechanical response of an argillaceous rock: experimental results and modelling

This extended abstract presents the key features of a THM analysis carried out to analyze the thermo-hydro-mechanical response of a mudstone under thermal loading. The analysis was performed in parallel with a large scale heating test. The good agreement observed between the measurements and the numerical results provides an incomparable validation of the model.Peer ReviewedPostprint (published version

Modelling of a deep excavation in a stiff clay

This extended abstract presents an interpretation of the response of a mudstone during the excavation of a shaft at high depths (500m). Instrument layout and numerical model are described. A very good agreement is observed between the field measurements and computed values.Peer ReviewedPostprint (published version

In situ behaviour of a stiff layered clay subject to thermal loading: Observations and interpretation

The paper presents an interpretation of an in situ heating test carried out on Opalinus clay in the Mont Terri underground laboratory. Opalinus clay is a stiff, strongly bedded, Mesozoic clay of marine origin. When subjected to thermal loading, saturated stiff clays exhibit 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 clay behaviour. Numerical analyses have been based on a coupled theoretical formulation that incorporates a constitutive law especially developed for this type of material. The law includes degradation of bonding by damage. By performing three-dimensional computations, it has been possible to incorporate anisotropy of material parameters and of in situ stresses. The 3D simulation has proved able to furnish a satisfactory representation of the development of the in situ test and of the main observed patterns of behaviour. A sensitivity analysis has also been carried out to examine the potential effect of various key or uncertain parameters. The critical examination of test observations and the results of the numerical analyses have allowed the classification, by differing degrees of significance, of the various coupled phenomena present in the proble

In situ behaviour of a stiff layered clay subject to thermal loading: Observations and interpretation

George Stephenson Medal 2008, atorgada per la Institution of Civil Engineers del Regne UnitThe paper presents an interpretation of an in situ heating test carried out on Opalinus clay in the Mont Terri underground laboratory. Opalinus clay is a stiff, strongly bedded, Mesozoic clay of marine origin. When subjected to thermal loading, saturated stiff clays exhibit 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 clay behaviour. Numerical analyses have been based on a coupled theoretical formulation that incorporates a constitutive law especially developed for this type of material. The law includes degradation of bonding by damage. By performing three-dimensional computations, it has been possible to incorporate anisotropy of material parameters and of in situ stresses. The 3D simulation has proved able to furnish a satisfactory representation of the development of the in situ test and of the main observed patterns of behaviour. A sensitivity analysis has also been carried out to examine the potential effect of various key or uncertain parameters. The critical examination of test observations and the results of the numerical analyses have allowed the classification, by differing degrees of significance, of the various coupled phenomena present in the problem.Peer ReviewedAward-winningPostprint (published version

Applications of multiphysical geomechanics in underground nuclear waste storage

Deep geological disposal in suitable host rocks is the favoured strategy for the storage and disposal of heat-emitting high level nuclear waste. A rational design of repositories requires a good understanding of the interacting thermo-hydro-mechanical phenomena that occur in the engineered barrier and adjacent rock. To this end, a multiphysical formulation is described that allows the performance of coupled THM analyses capable of reproducing observed phenomena. The formulation and computer code is applied to the simulation of two large scale tests: a mine-by test involving the excavation of a shaft in an argillaceous rock and a large-scale high- temperature heating test in fractured rock

3D Interpretation of an in situ heating test in the callovo-oxfordian mudstone

In order to improve the understanding of the thermo-hydro-mechanical (THM) behaviour of the Callovo-Oxfordian Clay, an in situ heating test (TER experiment) has been realized by ANDRA at Meuse/Haute Marne URL during the last years. In this experiment, one power-control heater has been placed in a horizontal borehole and several heating phases realized at distinct levels of power. Around this heating borehole, 32 temperature sensors, 5 water pressure sensors and 2 extensometers were placed in 8 different boreholes. This abstract presents the interpretation works performed in parallel by running 3D THM simulations.Peer ReviewedPostprint (published version