Abstract In a geological repository, the disposal of radioactive waste will result in the creation of engineering voids. Bentonite is commonly proposed as a sealing material as a result of its high swelling capacity. As the bentonite expands, the non-uniform development of porewater pressure and its coupling to total stress within the bentonite, may impair homogenisation. In this study we present results from five laboratory tests performed on sodium- and calcium-based bentonites to examine their swelling potential and capacity to homogenise over extreme bentonite-to-void ratios. Results demonstrate that even under these extreme ratios, the bentonite is able to swell and ultimately fill each void, creating a small swelling pressure. The swelling pressure development is spatially complex and time-consuming, and does not appear to be influenced by friction. Instead, it is characterised by plastic yielding of the clay with 70%–80% of the volume change associated with clay expansion adjacent to the void. This leads to heterogeneity illustrated by the presence of persistent differential stresses and the non-uniform distribution of moisture contents. Increases in the moisture content were measured but did not always correlate with the development of swelling pressure. This disequilibrium of the system is likely a reflection of the test durations and the slow evolution in the rates of change in swelling and porewater pressure beyond 130 days. Given the length of the experimental tests presented here, the time required to achieve full homogenisation of the clay is likely to be many years, if it occurs at all. Gravity segregation was also present in horizontal tests, further impairing clay homogenisation. However, as presented in this paper, it is possible to define functional relationships describing the bentonite swelling potential across engineering voids of differing size. This information will assist in establishing a safety case for bentonite usage in geological radioactive waste disposal.

中文翻译：

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空隙空间封闭过程中的膨润土均质化

摘要 在地质处置库中，放射性废物的处置会导致工程空隙的产生。由于膨润土的高膨胀能力，膨润土通常被提议作为密封材料。随着膨润土的膨胀，孔隙水压力的不均匀发展及其与膨润土内总应力的耦合可能会损害均质化。在这项研究中，我们展示了对钠基和钙基膨润土进行的五项实验室测试的结果，以检查它们的膨胀潜力和在极端膨润土与空隙率下均质的能力。结果表明，即使在这些极端比例下，膨润土也能够膨胀并最终填充每个空隙，从而产生很小的膨胀压力。膨胀压力的发展在空间上复杂且耗时，并且似乎不受摩擦的影响。相反，它的特征是粘土的塑性屈服，70%–80% 的体积变化与空隙附近的粘土膨胀有关。这导致了不均匀性，表现为持续的差异应力的存在和水分含量的不均匀分布。测量了水分含量的增加，但并不总是与膨胀压力的发展相关。系统的这种不平衡可能反映了测试持续时间以及超过 130 天的膨胀和孔隙水压力变化率的缓慢演变。鉴于此处介绍的实验测试的长度，实现粘土完全均化所需的时间可能需要很多年，如果发生的话。水平测试中也存在重力偏析，进一步损害了粘土的均质化。然而，如本文所述，可以定义描述不同尺寸工程空隙中膨润土膨胀潜力的函数关系。该信息将有助于建立膨润土在地质放射性废物处置中的使用安全案例。