Abstract The FEBEX “in situ” test was performed at an underground laboratory in Grimsel (Switzerland) with the aim of studying the behaviour of components in the near-field of a nuclear waste repository. A gallery of 2.3 m in diameter was excavated through the granite and two heaters, simulating the thermal effect of the wastes, were placed inside, surrounded by a barrier of highly-compacted bentonite blocks. In 2015, after 18 years of operation, the experiment was dismantled. Some of the bentonite samples taken were tested in the laboratory to characterize, among others, their physical state and determine their permeability and swelling capacity. There were significant changes in water content and dry density across the bentonite barrier: their distribution was radial around the axis of the gallery, with the water content decreasing from the granite towards the axis of the gallery and the dry density following the inverse pattern. The swelling capacity of the samples was related to their position in the barrier. In the internal, drier part of the barrier an increase of the swelling capacity with respect to the reference bentonite was detected, whereas the samples from the external part swelled less than expected. This was attributed to the different salinity of the samples. The hydraulic conductivity was mainly related to the dry density of the samples and decreased with respect to the reference bentonite. This decrease was not related to the position of the samples and could be related to the microstructural reorganization of the bentonite during the 18-year operation –which brought about an average decrease in the pore size– and to the low hydraulic gradients applied to determine the permeability of the samples retrieved.

中文翻译：

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在屏障条件下压实膨润土 18 年后的水力和力学性能

摘要 FEBEX“原位”测试是在格里姆塞尔（瑞士）的一个地下实验室进行的，目的是研究核废料储存库近场中组件的行为。穿过花岗岩挖出一个直径为 2.3 m 的走廊，并在里面放置了两个加热器，模拟废物的热效应，周围环绕着高度压实的膨润土块。2015年，在运行18年后，该实验被拆除。所取的一些膨润土样品在实验室进行了测试，以表征其物理状态并确定其渗透性和溶胀能力。整个膨润土屏障的含水量和干密度发生了显着变化：它们的分布围绕廊道轴线呈放射状，含水量从花岗岩向廊道轴线递减，干密度遵循相反的模式。样品的溶胀能力与其在屏障中的位置有关。在隔离层内部较干燥的部分，检测到相对于参考膨润土的溶胀能力增加，而外部部分的样品溶胀程度低于预期。这归因于样品的不同盐度。水力传导率主要与样品的干密度有关，相对于参考膨润土有所降低。