Abstract The swelling properties of compacted bentonite have typically been studied by means of hydro-mechanical models. The question of how these properties are affected by changes in its chemical composition has been given much less attention. However, cation exchange reactions in montmorillonite interlayer or changes in salinity are known to affect the swelling properties of bentonite. In this paper, a hydro-chemo-mechanical (HCM) model is proposed to study the effects of reactive transport processes on the long-term evolution of swelling pressure of compacted bentonite under confined and partially saturated conditions. The HCM model is implemented in iCP, an interface between Comsol Multiphysics and PHREEQC and is calibrated using available experimental data. At the constitutive level, the hydro-mechanical Barcelona Basic model is extended to include the effects of cation exchange reactions between interlayer and bulk water, changes in salinity, and montmorillonite dissolution in highly alkaline environments. The geochemistry of bentonite is based on an advanced reactive transport model that couples solute transport by diffusion and advection with chemical reactions. An application case is presented to demonstrate the main HCM model features and its ability to predict long-term changes in bentonite swelling pressure. The performance of the sealing system for closure of the repository for radioactive waste in France is simulated under unsaturated and isothermal conditions over a period of 50,000 years. The HCM interactions of MX-80 bentonite with other near-field materials such as concrete and claystone are simulated to predict the evolution of the swelling pressure of the seal. The results show the potential of the proposed model for the performance assessment of repository components. Overall, the model predicts limited impact of geochemical alteration on the swelling pressure of the bentonite seals, which is mainly driven by cation exchange reactions between the Na-rich bentonite, the Ca-rich claystone, and the calcium and alkalis from concrete porewater.

中文翻译：

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膨润土膨胀长期演变的水化学力学模型

摘要 压实膨润土的溶胀特性通常通过水力学模型进行研究。这些特性如何受其化学成分变化影响的问题很少受到关注。然而，已知蒙脱石夹层中的阳离子交换反应或盐度的变化会影响膨润土的溶胀性能。在本文中，提出了一种水化学机械 (HCM) 模型来研究反应输运过程对密实和部分饱和条件下压实膨润土膨胀压力长期演变的影响。HCM 模型在 iCP 中实现，iCP 是 Comsol Multiphysics 和 PHREEQC 之间的接口，并使用可用的实验数据进行校准。在构成层面，水力机械巴塞罗那基本模型扩展到包括夹层和大量水之间的阳离子交换反应、盐度变化和高碱性环境中蒙脱石溶解的影响。膨润土的地球化学基于先进的反应迁移模型，该模型将通过扩散和平流的溶质迁移与化学反应相结合。提供了一个应用案例，以展示 HCM 模型的主要特征及其预测膨润土膨胀压力长期变化的能力。在 50,000 年的时间里，在不饱和和等温条件下模拟了法国放射性废物处置库封闭系统的性能。模拟 MX-80 膨润土与其他近场材料（如混凝土和粘土岩）的 HCM 相互作用，以预测密封件膨胀压力的演变。结果显示了所提出的模型对存储库组件的性能评估的潜力。总体而言，该模型预测地球化学蚀变对膨润土密封膨胀压力的影响有限，这主要是由富钠膨润土、富钙粘土岩以及混凝土孔隙水中的钙和碱之间的阳离子交换反应驱动的。