The FEBEX in situ test provided bentonite samples that had been submitted to the conditions of the engineered barrier of a nuclear waste repository for 18 years. These samples can be considered quite evolved from the microstructural point of view (aged, matured) when compared with samples prepared in the laboratory under shorter and more usual time scales. The barrier, composed of bentonite blocks, was hydrated with granitic groundwater under natural conditions while it was submitted to the thermal gradient generated by a heater mimicking the waste canister. Some of the samples were drilled between two bentonite blocks, therefore they were crossed along by an interface. The gas permeability of samples with and without interface was tested in the laboratory under different triaxial boundary conditions.

Samples with an interface drilled in the inner part of the barrier (i.e. closer to the heater and consequently drier) had higher gas permeability than samples of similar accessible void ratio (related to dry density and water content) with no interface, and it was necessary to apply higher confining pressures to reduce or suppress gas flow in them. Both observations point to the interface as a preferential pathway for gas flow in this kind of samples. In contrast, wetter samples drilled along interfaces of the external part of the barrier (which had very low accessible void ratio, because of the high saturation), had permeabilities similar to those corresponding to the same accessible void ratio in the reference, untreated bentonite. This would prove the healing of the interfaces between blocks as a result of full saturation. The importance of the testing boundary conditions, particularly with respect to confinement, on gas transport processes was also highlighted.

FEBEX原位测试提供了膨润土样品，这些样品已经在核废料处置库的工程屏障条件下提交了18年。与在更短和更常见的时间尺度上在实验室中制备的样品相比，从微观结构的角度（陈旧，成熟）可以认为这些样品是相当进化的。由膨润土块组成的屏障在自然条件下与花岗岩地下水水合，同时受到模拟废物罐的加热器产生的热梯度的影响。一些样品是在两个膨润土块之间钻的，因此它们被一个界面穿过。在不同的三轴边界条件下，在实验室中测试了带界面和不带界面的样品的透气性。

在隔离层内部（即更靠近加热器并因此更干燥的位置）钻有界面的样品比没有界面的相似可及空隙率（与干密度和水含量有关）的样品具有更高的透气性。施加更高的围压以减少或抑制其中的气体流动。两种观察都指出界面是这类样品中气体流动的优先途径。相反，沿屏障外部部分的界面（由于饱和度高而具有非常低的可及孔隙率）钻出的湿润样品的渗透率类似于未处理的膨润土中与参照中相同的可及孔隙率相对应的渗透率。这将证明由于完全饱和而修复了块之间的界面。