The hygro-mechanical behaviour of Tournemire argillite was studied by measuring the deformation induced by a desiccation process. The used non-invasive method called "Digital Image Correlation" (DIC) enables easily the measurements of strain fields during a physical transformation. A set of samples taken from the Tournemire site was submitted to a desaturation process in an oven at five temperatures: 40°C; 80°C, 105°C, 150°C and 200°C. Strain results have shown that the observed deformation mechanisms are mainly controlled by the rock heterogeneities (inducing strain localizations). The microcracks induced by desiccation were parallel to the bedding planes and located at the interface between non-clayey grains/heterogeneities (here calcite nodules) and the clay matrix. After a few hours of heating, a closure of these microcracks associated with a decrease of strain localizations was observed.

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