The thermal volume changes of the Callovo-Oxfordian claystone
Résumé
There are quite few data available about the thermal behaviour of claystones while their knowledge becomes necessary to better understand the behaviour of exothermic high-level radioactive waste confining systems during the thermal phase. In this paper, some aspects of the thermomechanical response of the Callovo-Oxfordian claystone, a possible host rock for radioactive waste in France, were investigated by using a new isotropic hollow cylinder isotropic cell. The short drainage path permitted in this device (half the thickness of the hollow cylinder) allows in low permeability materials a good saturation (conducted here under stress conditions close to in-situ) in a reasonably short time. It also ensures enhanced drainage conditions and reasonable homogeneity in pore pressure during drained isotropic compression and heating tests. The thermomechanical experimental programme conducted here evidenced a plastic contraction of the claystone during drained heating under in-situ stress conditions, like in normally consolidated soils. Previous loading induced a dilating-contracting response comparable to that of overconsolidated clays. Finally, whereas the elastic response appeared to be temperature independent, the plastic compressibility investigated through a drained isothermal isotropic compression test at 80°C increased compared to that at 25°C. These first results should be confirmed by further thermomechanical investigation on claystones.