Sur la sensibilité à l'EAU des argillites

Growing interest has been devoted to claystones in the framework of research about radioactive waste disposal at great depth. Claystones are weak rocks with significant sensitivity to changes in water content. Various evidences of damage induced either by stress application or by changes in water content have been observed. This paper describes some experimental evidences of damage induced in claystone during oedometer compression tests carried out on specimens of the Callovo-Oxfordian claystone coming from the deep underground research laboratory excavated by the French agency of radioactive waste management close to the city of Bure (East of France). Specimens were not completely saturated due to extraction and trimming. First evidence of damage is obtained when resaturating specimens previously brought back close to and above in-situ stress conditions: swelling is also observed, even under stress higher than the in- situ one. Enhanced swelling is also observed on saturated samples submitted to compression, the higher the stress, the higher the swelling. Swelling is interpreted by the generation of cracks and the mobilisation within them of swelling due to the hydration of the smectites included in the clay matrix. Such cracks may either be due to drying, wetting or to compression. Cracks enhance swelling, evidencing the coupling between damage and swelling, an illustration of the water sensitivity of claystones.