Numerical Analysis of the Thermo-Hydromechanical Behaviour of Underground Storages in Hard Rock

Understanding the thermal impact on the hydro-mechanical behavior of the host rock is one important issue in the design of underground storages for the high level radioactive wastes. Increasing temperature inevitably affects the rock mass stability with the generation of overpressure and associated mechanical affects. Consequently, it is essential that the designer of an underground storage has appropriate knowledge of the coupled thermal and hydromechanical behaviour of the rock mass. In this paper, an in situ thermal-hydromechanical test is studied. This test consists to heat the host rock by one heating element of 3 meters length with two successive supplied heating powers: 275W and 915W. In the test, the temperature in the storage was increased up to 100° C with a monitor system equipped approximately 50 temperature, pore water pressure and deformation/displacement sensors in order to investigate the response of argillites in different heating phases. The Mohr-Coulomb constitutive model and the FLAC3D numerical code are used for prediction and interpretation of the measurements. The evolutions of temperature, pore-water pressure and strain during heating phases and cooling phase have been simulated and compared with in situ measurements. The good concordance between the numerical simulations and measurement data allow us to identify the in situ THM parameters of argillite and understand the coupled phenomena observed in the experiment.