Suction effects in deep Callovo-Oxfordian claystone

International audienceAn experimental program aimed at investigating suction effects in a specimen of Callovo-Oxfordian claystone extracted at great depth (479 m) was carried out. A specimen that was saturated in an oedometer with limited swelling exhibited significant swelling and desaturation upon quick unloading at constant water content. The microstructure after unloading was compared to the initial one based on mercury intrusion porosimetry measurements. Since the pore size distribution curves before and after loading appeared to be comparable in the range of pore sizes covered by mercury intrusion (entrance diameter between 363.6 µm and 5.5 nm), it was concluded, based onmicrostructure considerations, that swelling occurred in pores with diameter smaller than 5.5 nm, from a water transfer within the clay matrix from inter-platelets to intra-platelets pores. This mechanism might occur when excavating galleries in areas of the Excavation damaged zone that support instantaneous unloading sequences, as a first desaturation process prior to subsequent evaporation due to the ventilation of galleries