Numerical modelling of the hydro-mechanical behaviour of unsaturated COx

This paper presents a modified Biot's model for describing the hydromechanical behaviour of the Callovo-Oxfordian Argillite (COx) Claystone. The COx Claystone exhibits significant deformation during water desaturation/resaturation, and the standard Biot's model is unable to predict the large shrinkage/swelling of the material. The authors then introduced an additional swelling/shrinkage law to simulate large deformations upon changes in water content. This added deformation law is calibrated against the difference between measurements from laboratory tests and predictions from the standard Biot's model. The plastic-damage model, developed by Fichant et al. for concrete, is used to describe the mechanical behaviour of the solid skeleton of the COx Claystone. In particular, the stress-strain relation is described in a damage-based model, while the plastic behaviour relies on the Nadai criterion. The validation of the proposed model is performed by numerical simulation of (a) uniaxial compression tests under different relative humidities of 32, 44 and 76%; (b) triaxial compression tests at confining stresses of 0, 2, 6 and 12 MPa under relative humidity of 90%; (c) free deformation desaturation-resaturation paths; (d) resaturation swelling tests under a constant axial load; and (e) axial swelling pressure tests. Comparison of the results from the aforementioned numerical simulations with experimental data demonstrates the capability of the proposed model to describe accurately the hydromechanical behaviour of the COx Claystone.