AbstractThe corrosion of waste canisters in the deep geological disposal facilities (GDFs) for highâlevel radioactive waste (HLRW) can generate gas, which escapes from the engineered barrier system through the interfaces between the bentonite buffer blocks and the host rock and those between the bentonite blocks. In this study, a series of water infiltration and gas breakthrough experiments were conducted on granite and on graniteâbentonite specimens with smooth and grooved interfaces. On this basis, this study presents new insights and a quantitative assessment of the impact of the interface between clay and host rock on gas transport. As the results show, the water permeability values from water infiltration tests on granite and graniteâbentonite samples (10â19â10â20 m2) are found to be slightly higher than that of bentonite. The gas permeability of the mockâup samples with smooth interfaces is one order of magnitude larger than that of the mockâup with grooved interfaces. The gas results of breakthrough pressures for the granite and the graniteâbentonite mockâup samples are significantly lower than that of bentonite. The results highlight the potential existence of preferential gas migration channels between the rock and bentonite buffer that require further considerations in safety assessment.