Thermal impact on the excavation damage zone around a supported drift using the 2nd gradient model

The temperature increase induced by radioactive waste decay generates
the thermal pressurisation around the excavation damage zone (EDZ),
and the excess pore pressure could induce fracture re-opening and propagation.
Shear strain localisation in band mode leading to the onset
of micro/macro cracks can be always evidenced before the fracturing
process from the lab experiments using advanced experimental devices,
hence the thermal effects on the rock behaviour around the EDZ could
be modelled with the consideration of development of shear bands. A
coupled local 2nd gradient model with regularisation technique is implemented,
considering the thermo-hydro-mechanical (THM) couplings in
order to well reproduce the shear bands. Furthermore, the thermo-poroelasticity
framework is summarized to validate the implemented model.
The discrepancy of thermal dilation coefficient between solid and fluid
phases is proved to be the significant parameter leading to the excess
pore pressure. Finally, an application of a heating test based on Eurad
Hitec benchmark exercise with a drift supported by a liner is studied. The
strain localisation induced by thermal effects is properly reproduced. The
plasticity and shear bands evolutions are highlighted during the heating,
and the shear bands are preferential to develop in the minor horizontal
principal stress direction. Different shear band patterns are obtained with
changing gap values between the drift wall and the liner. A smaller gap
between the wall and the liner can limit the development of shear bands.