Experimental study of the hydro-mechanical behaviour of the Callovo-Oxfordian argillite

Various laboratory experiments were carried out in the framework of the MODEX-REP project on the Callovo-Oxfordian argillite core samples taken from the Meuse/Haute-Marne Underground Research Laboratory (MHM-URL) in Eastern France to provide basic data for modelling the hydro-mechanical response of the argillite to shaft sinking. The short-term mechanical behaviour of the argillite was investigated by means of uniaxial and triaxial compression tests, whereas the long-term behaviour was studied by uniaxial creep and relaxation tests. Some influence factors such as material anisotropy, scale effect, water content and sample origin were examined. Permeability of the argillite was determined on wet and dry specimens parallel and perpendicular to the bedding plane by using gas under different confining pressures. With regard to the short-term mechanical behaviour, scale and anisotropy effects were observed. The compressive strength and the failure strain of the air-dried specimens are about two times higher than those of the saturated ones. No lower creep limit, no significant scale effect and no significant anisotropy effect on the pure creep behaviour for the argillite were found. The long-term mechanical behaviour of the investigated region of the argillaceous formation is relatively homogeneous. The gas permeability parallel to the bedding plane is about one order of magnitude higher than that perpendicular to the bedding and decreases with increasing confining pressure and water content.