Treatment and exploitation of time series of pressure and temperature obtained in the experimental argillaceous site of Tournemire
Titre du congrès :Clays in natural and engineered barriers for radioactive waste confinement
Ville du congrès :Tours
Date du congrès :14/03/2005
Compacted argillaceous semi-permeables are potential geological formations for the deep repository of radioactive wastes, due to their very low permeability and to their capacity of radionuclide retention. In this framework, IRSN develops its own research programmes in its experimental station of Tournemire (Aveyron, France). This laboratory is located in a century-old tunnel crossing an argillite formation 250m thick from Toarcian and Domerian.
Since 1990, 18 boreholes have been realized with the aim of acquiring among others, the hydraulic characteristics of the argillaceous formation and of its bounding aquifers. Seven boreholes, equipped with twenty sensors, have been followed for the pressure and temperature of the pore and fracture waters with an acquisition each half of an hour. The barometric pressure and temperature in the tunnel were also recorded in the same period.
The aim of this work was to treat all of these time series by means of mathematical tools with the goal of extracting signals emitted at the massif scale and likely to inform us about its global hydraulic functioning. This information will be compared to that acquired, at the very local scale, by hydraulic tests.
From an instrumentation point of view, temperature measurements obtained by thermistance have required a correction that has demonstrated a strong instability to low frequencies and have not allowed their full exploitation. In the future, it is recommended to use platinum probes. All the data were submitted to a multiple treatment including: spectral and correlation analyses, 1/f noise analysis, continuous wavelets analyses, simple and crossed multi-resolution analyses, and at last, reconstructed attractors analyses. The analysis of borehole pressure and temperature data has revealed the influence of Earth tides (fig. 1) in the unfractured semi-permeable and its bounding aquifers constituted by the Carixian and Aalenian formations