ROCK TUNNELS | DEEP REPOSITORY R&D FOR RADIOACTIVE WASTE


7 6 5


4 3 2


1 0


1200 1250 1300 1350 1400 1450 1500 1550 Dry density [Kg m-3


] 1600


Experimentation results Simulation results


Bernachy-Barbe et al. 2020


Top, figure 7: Experimental (Bernachy-Barbe et al. 2020) and simulation results for constant volume swelling pressure tests on bentonite pellets/powder mixture


Centre, figure 8: Experimental (LAEGO-ENSG for Andra) and simulations results for odometer test on backfill material


Bottom, figure 9: Three-linear elastic law employed for the compressible lining


This aspect of the model does not allow


regularising the problem of strain localisation associated with softening. Further work using a non-local model as a regularisation technique has been presented by Mánica et al. (2022), for 2D applications. But the huge computational resources required by


0.8


0.75 0.7


0.65 0.6 0.55 0.5


0.45 0.4 100 101 102 Vertical stress [kPa] 103 104


Experimentation results Simulation results


these techniques in large 3D geometries make its application currently impracticable for the problem under consideration. For this reason, the local model presented by Mánica et al. (2017) is employed at this stage. Considerations about the representativeness of the solution obtained using this model are discussed. The model assumes that the total strain increment


can be decomposed into elastic, plastic and creep strain increments. The first two are described within the framework of elasto-plasticity, and for the latter there is an additional time-dependent element employed. The Mohr–Coulomb criterion is adopted for both


yield and failure limits. Strain–stress relation is given by a generalised cross-anisotropic Hooke’s law type (with five independent elastic parameters). Strength anisotropy is included through a non-uniform scaling of the stress tensor (Manica et al. 2016). After reaching the yield limit, an isotropic non-linear


hardening/softening mechanism is considered. The evolution of strength parameters is controlled by the equivalent plastic strain. Friction angle varies in a piecewise manner. Cohesion


Young’s modulus { 4 2 0 0 0.1 0.2 0.3 Strain [-] 26 | February 2025 0.4 0.5 0.6


E = 100 MPa E = 3 MPa


E = 100 MPa for for for ɛ ≤ 0.015


< ɛ ≤ 0.515 ɛ > 0.515


varies in parallel with the friction angle. Creep strain rates are higher at higher deviatoric stresses, and decrease as creep strains accumulate over time. Finally, the increase of permeability with irreversible


strains is incorporated into the model by including a dependency of the intrinsic permeability on the equivalent plastic strain. The model was validated by reproducing and


comparing results of triaxial and creep laboratory tests on COx claystone (Manica et al. 2017). It has also been shown to reproduce, in the context of a Transverse Action benchmark programme, the extension and shape of the EDZ in a 5m-diameter drift in the Meuse/ Haute- Marne Underground Research Laboratory (MHM- URL) at Bure (Seyedi et al. 2017). For the simulations presented in this paper, the host


rock parameters have been completed by parameters obtained from more recent laboratory and field data.


Stress [MPa]


Void ratio [-]


Swelling pressure [MPa]


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