Thermo-Hydro-Mechanical analysis of a Callovo – Oxfordian clay
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The main objectives of the Thesis are as follows: (i) to observe and investigate the response of an argillaceous soft rock, the COX clay to heating and cooling during the TED experiment; (ii) to analyse THM processes taking place in the rock around the heaters and to compare the modelling results with the field measurements for validation of the models; and (iii) to characterize THM properties of the COX clay by means of sensitivity analyses. In order to attain these objectives various 3D simulations have been performed. A 3D simulation has allowed the incorporation of anisotropic material properties and anisotropic in situ stress state. Considering that the thermal conductivity of the material does not change, because in low permeability media the only significant heat transport mechanism is heat conduction, a series of purely thermal analyses have been performed to find the value of thermal conductivity that achieves the closest agreement with measured temperatures. The aim of these analyses is the interpretation of the temperature field obtained during the heating experiment and the obtainment of the thermal parameters to analyse the temperature change in the TED experiment. Afterwards, a series of coupled THM analyses have been performed in order to reproduce the entire experiment and to study the influence of the main THM parameters of the COX clay. The pore pressure response to thermal loading increases with temperature increase due to the differential thermal expansion of the water and the solid; but when the temperature increase rate diminishes, the established pore pressure gradient is dissipated at a velocity depending on the permeability of the medium. A pore pressure analysis has been performed in order to evaluate the interplay between temperature and pore pressure, as well as to study the influence of the bedding plane on the pore pressure. A sensitivity analysis has also been carried out to assist in the interpretation of the test and to achieve an enhanced understanding of the phenomena involved.