An original constitutive law for Callovo-Oxfordian argillite, a two-scale double-porosity material

As in Biot's theory, Biot's tensor in the proposed stress state equation of Callovo-Oxfordian argillite weighs in a hydro-mechanical coupling term the pressure variation in the interparticle pores. Because of the particular microstructure of Callovo-Oxfordian argillite, Biot's tensor cannot be determined by a classic triaxial “change in pore” pressure poromechanical test. An original methodology is proposed to determine this tensor, which uses the monitoring of the length variation of a sample during a free-drying. Biot's tensor is found to be almost isotropic, with a Biot's coefficient equal to 0.84.