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Article Dans Une Revue The Geological Society, London, Special Publications Année : 2007

Temperature-induced evolution of the elastic and magnetic anisotropy in argillite samples from Bure underground research laboratory, eastern France

C. David
J. Colombier
  • Fonction : Auteur

Résumé

Abstract The influence of temperature on magnetic and elastic properties of the Callovo-Oxfordian argillite formation, host of the French underground research laboratory for studying radioactive waste repository, has been investigated following two types of experiments. In the first experiment, rock samples were heated at 95 °C in an oven for 41 days, and in the second, heating–cooling cycles at increasing maximum temperatures were applied. Magnetic susceptibility and P-wave velocity measurements were conducted to investigate the effect of heating not only on the absolute values but also on the anisotropy. Whereas little variation was observed in the first experiment, the results of the heating–cooling cycles showed that different stages can be identified in the evolution of P-wave velocity and magnetic susceptibility with maximum temperature applied. At temperatures below 200 °C, the velocity increases sharply whereas the magnetic susceptibility remains unchanged: this is interpreted as being the result of mineralogical transformations, probably associated with dewatering of the clays. Above 200 °C, a large increase in susceptibility associated with a levelling off (or even a decreasing trend) of the velocity results from the competition between thermal cracking processes and another kind of mineralogical transformation affecting both properties. A magnetic mineralogical study showed that the main ferromagnetic mineral present is magnetite. An interesting result of the study is that in the temperature range investigated, the elastic properties are enhanced and the anisotropy is increased by raising the temperature, which has important consequences for the seismic monitoring of the storage site.

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P. Robion, C. David, J. Colombier. Temperature-induced evolution of the elastic and magnetic anisotropy in argillite samples from Bure underground research laboratory, eastern France. The Geological Society, London, Special Publications, 2007, 284 (1), pp.57-69. ⟨10.1144/SP284.5⟩. ⟨hal-03480610⟩

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