This study focuses on assessing the effect of short- and long-term nonlinear deformation (plasticity and creep) on the thermo-hydro-mechanical (THM) responses of Callovo-Oxfordian (COx) claystone, considered as the host formation for the geological radioactive waste disposal in France, if it is licensed. The temperature increase due to heat emitted from the waste package induces a pore pressure rise in low permeability porous rocks such as the COx claystone, due to the difference in the thermal expansion coefficients between water and the argillaceous skeleton. This phenomenon has been evidenced by laboratory and in situ heating experiments. Recently, the key THM phenomena taking place around the high-level radioactive waste (HLW) repository based on the French concept, have been investigated using a thermoporoelasticity approach. In this paper, certain nonlinearities observed in the mechanical behaviour of the COx claystone have been considered in the evaluation of these THM processes. Three numerical simulations (thermoporoelastic, thermoporoelastoplastic and thermoporoelastoviscoplastic) are performed using Comsol Multiphysics code, in which the time-dependent behaviour of the COx is described by a power law whereas the elastoplastic behaviour is modelled by a strain hardening with a Hoek-Brown criterion and a non-associative flow rule. The role of elastoplastic and viscoplastic parts of deformations on the temperature, pore pressure and stresses time evolution in the far-field, is highlighted.

中文翻译：

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短期和长期非线性行为对 COx 粘土岩热孔隙力学加压的影响

本研究重点评估短期和长期非线性变形（塑性和蠕变）对 Callovo-Oxfordian (COx) 粘土岩热-水-机械 (THM) 响应的影响，该粘土岩被认为是地质放射性的宿主地层。如果获得许可，可在法国进行废物处理。由于水和泥质骨架之间的热膨胀系数不同，废物包散发的热量导致温度升高，导致低渗透性​​多孔岩石（例如COx粘土岩）的孔隙压力升高。这种现象已被实验室和原位加热实验所证实。最近，基于法国概念的高放放射性废物（HLW）储存库周围发生的关键 THM 现象已使用热孔隙弹性方法进行了研究。在本文中，在评估这些 THM 过程时考虑了 COx 粘土岩机械行为中观察到的某些非线性。使用 Comsol Multiphysics 代码执行三种数值模拟（热孔弹性、热孔弹塑性和热孔弹粘塑性），其中 COx 的时间相关行为由幂律描述，而弹塑性行为则通过采用 Hoek-Brown 准则的应变硬化来建模，非关联流规则。强调了变形的弹塑性和粘塑性部分对远场温度、孔隙压力和应力时间演化的作用。