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

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

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

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

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

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

Elastoplastic modelling of a ventilation test in argillaceous rock

A full scale field test to evaluate the effects of ventilation in a tunnel excavated in Opalinus clay has been performed in the underground laboratory of Mont Terri in Switzerland. The test involved several stages of wetting and drying under controlled conditions. To aid interpretation, coupled hydromechanical analyses have been performed taking into account the specific features of the test, especially the conditions in the boundary between air and clay. An elastoplastic model has been used to describe the mechanical behaviour of the rock. The results have revealed 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. Observed ventilation effects on Opalinus clay have been modest and reduced to zones quite close to the tunnel

Predictive modelling of an excavation test in indurated clay

This abstract presents the predictive hydromechanical (HM) modelling of an excavation performed in Opalinus clay in the Mont Terri underground laboratory.Peer ReviewedPostprint (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.Peer ReviewedPostprint (author’s final draft