Abstract Bentonite is considered for engineered barriers in radioactive waste geological repositories due to its low permeability, swelling pressure and radionuclide retention properties. The French concept favors the use of bentonite under granular form - pellets and crushed pellets mix - for an easier building of plugs and seals relatively to bricks. However, this introduces a significant degree of macroscopic initial heterogeneity (at several scales) that is expected to disappear via mass redistribution during resaturation in order to obtain homogeneous hydraulic and mechanical performance. This also may have practical effects on the reliability of results from tests with small volumes of bentonite compatible with the time scales manageable at the laboratory. In this study, isochoric swelling pressure tests at various densities and sample sizes were carried out and evidenced bias mainly due to the size of the cell compared to the size of the pellets, although the average density is equivalent, pointing towards incomplete homogenization. Large-scale swelling pressure tests, however, converged towards values previously measured for more finely grained materials. Local pressure measurements also evidenced some stress heterogeneities that do not seem to disappear at medium time-scales. These stress heterogeneities could be correlated to local density variations of the final state assessed using destructive measurements and X-ray computed tomography.

中文翻译：

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观察到 MX-80 膨润土在颗粒/粉末形式下水合后的不均匀性

摘要 膨润土因其低渗透性、膨胀压力和放射性核素保留特性而被认为是放射性废物地质处置库中的工程屏障。法国的概念倾向于使用颗粒形式的膨润土 - 颗粒和粉碎的颗粒混合物 - 相对于砖更容易建造塞子和密封件。然而，这引入了显着程度的宏观初始异质性（在几个尺度上），预计在再饱和期间通过质量重新分布消失，以获得均匀的水力和机械性能。这也可能对与实验室可管理的时间尺度兼容的少量膨润土的测试结果的可靠性产生实际影响。在这项研究中，进行了各种密度和样品尺寸的等容溶胀压力测试，并证明了偏差主要是由于与颗粒尺寸相比，电池的尺寸，尽管平均密度是相等的，表明均质化不完全。然而，大规模溶胀压力测试趋向于先前为更细粒度材料测量的值。局部压力测量还证明了一些应力异质性，这些异质性似乎在中等时间尺度上不会消失。这些应力异质性可能与使用破坏性测量和 X 射线计算机断层扫描评估的最终状态的局部密度变化相关。指向不完全同质化。然而，大规模溶胀压力测试趋向于先前为更细粒度材料测量的值。局部压力测量还证明了一些应力异质性，这些异质性似乎在中等时间尺度上不会消失。这些应力异质性可能与使用破坏性测量和 X 射线计算机断层扫描评估的最终状态的局部密度变化相关。指向不完全同质化。然而，大规模溶胀压力测试趋向于先前为更细粒度材料测量的值。局部压力测量还证明了一些应力异质性，这些异质性似乎在中等时间尺度上不会消失。这些应力异质性可能与使用破坏性测量和 X 射线计算机断层扫描评估的最终状态的局部密度变化相关。