A laboratory investigation of thermally induced pore

1 pressures in the Callovo-Oxfordian Claystone 2 3 M. Mohajerani, P. Delage, J. Sulem, M. Monfared, A.M. Tang, B. Gatmiri 4 5 1. Ecole des Ponts ParisTech, UR Navier/CERMES, 6-8 av. B. Pascal, F 77455 Marne la Vallée cdx 2 6 2. ANDRA, Châtenay Malabry 7 8 9 International Journal of Rock Mechanics and Mining Sciences, 2012, vol. 52, 112-121, 10 doi:10.1016/j.ijrmms.2012.02.012. 11 12 13 Abstract 14 In the framework of research into radioactive waste disposal, it was decided to investigate the 15 thermally induce pore pressure occurring in the Callovo-Oxfordian claystone, a possible host 16 rock in which the ANDRA underground laboratory of Bure (East of France) has been 17 excavated. Thermal pore pressures appear in low permeability soils and rocks because the 18 thermal expansion coefficient of water is significantly higher than that of the solid grains 19 (Campanella and Mitchell; 1968 [1], Ghabezloo and Sulem; 2009 [2]). This phenomenon has 20 clearly been observed in various in-situ heating tests conducted in Opalinus claystone in the 21 Mont-Terri Underground Research Laboratory (URL) in Switzerland (HE-D test) and in 22 Callovo-Oxfordian (COx) claystone in the Bure URL in France (TER test, Wileveau and Su; 23 2007 [3]) 24 The processes of coring, transportation, storage and specimen trimming induce some 25 desaturation in the sample. Due to the very low permeability (10 m) of the COx claystone, 26 a long period of time is necessary to properly resaturate the sample, a mandatory condition to 27 satisfactorily investigate thermal pressurisation. Particular emphasis was hence put on the 28 previous saturation procedure that was carried out under in-situ effective stress condition. 29 Thermal pressurization has been investigated by performing undrained heating tests while 30 measuring pore pressures changes in a specially adapted thermal isotropic compression cell. 31 Special care was devoted to calibration procedures to account for the effects of the system on 32 the pore pressure measurements. The thermal pressurization coefficient measured appeared to 33 change with temperature, mainly because of the changes with temperature of both the water 34 thermal expansion coefficient of water and the drained compression coefficient of the 35 claystone. 36 37