To ensure the performance efficiency and long-term operational safety of the engineering barrier in deep geological repositories, it is of great importance to investigate gas migration behavior in the water-saturated bentonite subjected to decay heat generated by the nuclear waste. In this work, experimental investigations were conducted to find out influences of multi-step thermal cycles on variations of the effective gas permeability, gas breakthrough pressure and microstructure of the bentonite specimens. A temperature range of 20–60 °C was selected and each temperature step was kept constant for at least 3–4 days to allow the gas flow to be equilibrated. Results show that effective gas permeability increases with heating, while decreases with cooling. The effective gas permeability decreases from 7.9 × 10⁻²³ to 2.01 × 10⁻²³ m² for the specimen tested under a constant injection pressure of 1.52 MPa after experienced one to three thermal cycles. Meanwhile, the gas breakthrough pressure for GMZ bentonite after experiencing three thermal cycles was 2.43 MPa. Microstructural observations by the MIP tests and paraffin-coated tests indicate that the heating-cooling cycles induce decreases of void space, resulting from the shrinkage of the bentonite matrix. Decrease of macro-pores and a little increase of micro-pores induced by the thermal cycles applied could make it difficult for gas to break through the bentonite matrix. The interfacial effect is the dominant gas breakthrough mechanism for specimens experienced thermal cycles.

为了确保深层地质库中工程屏障的性能效率和长期运行安全性，研究受核废料产生的衰变热作用的水饱和膨润土中的气体迁移行为至关重要。在这项工作中，进行了实验研究以发现多步骤热循环对膨润土样品的有效气体渗透率，气体穿透压力和微观结构变化的影响。选择的温度范围为20–60°C，每个温度步骤至少要保持3–4天保持恒定，以使气流平衡。结果表明，有效气体渗透率随加热而增加，而随冷却而降低。有效气体渗透率从7.9×10 ^-23降低在经历一到三个热循环后，在1.52 MPa的恒定注射压力下测试的样品的最大^应力为2.01×10 ^-23  m ²。同时，经历三个热循环后的GMZ膨润土的气体穿透压力为2.43 MPa。通过MIP试验和石蜡涂层试验进行的微观结构观察表明，加热和冷却循环会导致膨润土基质收缩，从而导致空隙空间减少。施加的热循环引起的大孔的减少和微孔的少量增加可能使气体难以穿透膨润土基质。对于经历热循环的样品，界面效应是主要的气体突破机理。