The aim of this paper is to investigate the long-term hydro-mechanical behaviour of a highly heterogeneous MX80 bentonite pellet/powder mixture (80/20 in dry mass), which is one of the candidate sealing materials in deep geological repositories. In spite of the operational advantages related to the use of the mixture, structural heterogeneities resulting from the installation process constitute a matter of concern and require special approaches to describe adequately the material behaviour during hydration. In this study, a double structure formulation taking into account the initial structural heterogeneity of the material as well as damage to pellets upon wetting is proposed. The formulation is applied to the modelling of a 1/10 mock-up of Sealex large-scale tests. Hydraulic and mechanical parameters are determined from an extensive laboratory programme carried out on a single pellet of bentonite and on the pellet/powder mixture. To ensure an adequate analysis of the test, the initial heterogeneous structural distribution of the material is determined by image analysis of microfocus X-ray computed tomography observations. The model allows the anisotropic swelling behaviour of the mixture to be satisfactorily reproduced when accounting for the spatial variation of the material's initial porosity. In particular, the long-term (decade) hydro-mechanical behaviour of the mixture can be well described. Detailed analysis of the modelling results demonstrates the existence of dry density gradients at the long term and their influence on swelling pressure anisotropy.

中文翻译：

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考虑初始结构异质性，对膨润土粒料/粉末混合物的长期水力学行为进行建模

本文的目的是研究高度异质的MX80膨润土颗粒/粉末混合物（以干质量计为80/20）的长期流体力学行为，该混合物是深层地质储层中的候选密封材料之一。尽管与使用混合物相关的操作优势，但安装过程中产生的结构异质性仍是一个令人关注的问题，并且需要采取特殊方法来充分描述水合过程中的材料性能。在这项研究中，提出了一种双重结构配方，其中考虑了材料的初始结构异质性以及润湿时对颗粒的损害。该公式适用于Sealex大规模测试1/10模型的建模。液压和机械参数是根据对单个膨润土颗粒和颗粒/粉末混合物进行的广泛实验室程序确定的。为了确保对测试进行足够的分析，通过微焦点X射线计算机断层扫描观察的图像分析来确定材料的初始异质结构分布。当考虑材料初始孔隙率的空间变化时，该模型可以令人满意地再现混合物的各向异性膨胀行为。特别地，可以很好地描述混合物的长期（十年）水力力学性能。对模型结果的详细分析表明，长期存在干密度梯度及其对膨胀压力各向异性的影响。