Abstract During the long-term evolution process of the geological repository, the gas permeability evolution of the buffer material is critical to its sealing performance evaluation. The purpose of this study is to investigate the gas permeability evolution of unsaturated GMZ bentonite under the coupled effect of stress-saturation gradient-gas pressure. First, the samples were held at different relative humidities and frees-swelling conditions to simulate the in-situ saturation gradient. The results show that the water absorption (or loss) of bentonite can affect its water content, dry density and porosity, further affecting its gas permeability characteristics. The evolution of the gas permeability is influenced by the coupling of these factors, which is between 10−19 and 10−15 m2. During the first cycle of low confining pressure, the results show that the values of the gas permeability are very close, despite the large difference in water contents. Further analysis found that in addition to the water content, the change in pore structure (pore volume) also affects the gas permeability. The effects of the two basically offset each other, and as a result, the change in gas permeability is not very clear. After undergoing a cyclic loading and unloading, the evolution of gas permeability strictly follows the water content relationship between the samples. Therefore, the water content plays a predominant role at this stage. In addition, the microscopic image (after permeability tests) shows that the bentonite sample possesses a dense pore structure at high water content, that graininess is strong at low water content, and that a large number of pores exist. Regarding the effect of the gas pressure, it is found that the effect of gas pressure on the gas permeability is more evident at low water content. Gas does not adhere to the pore walls as liquid does, and the slippage of gases along the pore walls gives rise to an apparent dependence of permeability on pressure.

中文翻译：

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水力-机械耦合作用下压实GMZ膨润土透气性的实验室研究

摘要 在地质处置库长期演化过程中，缓冲材料的气体渗透率演化对其密封性能评价至关重要。本研究的目的是研究在应力-饱和梯度-气压耦合作用下不饱和GMZ膨润土的气体渗透率演化。首先，将样品保持在不同的相对湿度和自由膨胀条件下以模拟原位饱和梯度。结果表明，膨润土的吸水（或失水）会影响其含水量、干密度和孔隙率，进而影响其透气特性。气体渗透率的演变受这些因素的耦合影响，在 10-19 和 10-15 m2 之间。在第一个低围压循环中，结果表明，尽管水含量差异很大，但气体渗透率的值非常接近。进一步分析发现，除了含水量外，孔隙结构（孔隙体积）的变化也会影响气体渗透率。两者的影响基本相互抵消，因此透气性的变化不是很明显。经过循环加载和卸载后，气体渗透率的演变严格遵循样品之间的含水量关系。因此，水含量在这个阶段起主导作用。此外，显微图像（渗透性测试后）表明，膨润土样品在高含水量时具有致密的孔隙结构，在低含水量时颗粒感强，并且存在大量孔隙。关于气体压力的影响，发现低含水量时气体压力对气体渗透率的影响更为明显。气体不像液体那样粘附在孔壁上，气体沿着孔壁滑移导致渗透率明显依赖于压力。