Characterization of the transversely isotropic behaviour of the callovo-oxfordian claystone in thermo-hydro-mechanical experiments

Thermo-hydro-mechanical (THM) couplings in the behavior of the Callovo- Oxfordian claystone were investigated in a laboratory study. We measured the transversely isotropic response of the claystone to mechanical, hydraulic and thermal loads. Parameters in drained and undrained conditions are evaluated. Given the low permeability of the material (in the order of 10-21 m2), the achievement of specimen saturation and pore pressure equilibrium during tests requires generally long durations. An adapted transient step loading procedure, presented by Braun et al. (2019), was applied for isotropic tests in drained and undrained conditions, and under thermal and mechanical loading. Various material parameters were determined. We evidenced a ratio between strains perpendicular and parallel to bedding around with a value around 3 for drained hydromechanical loadings and undrained thermal loading. In undrained compression, a ratio of around 2 was evidenced. For drained thermal loading, this ratio was slightly smaller than 1.