Bentonite or Sand bentonite mixtures are often considered as a promising candidate as buffer material for isolation of high-levelradioactive waste in a deep geological repository (DGR).Under the synergic effect of heat from radioactive decay and moisture infiltration from the host rock, the buffer material experiences changes in thermo-hydro-mechanical properties, which affect the performance of the buffer material.The design and safety assessment of DGR solicits commanding knowledge about the coupled heat and moisture transfer occurring in such systems. Given this, the present numerical study is intended to analyze the suitability of sand bentonite mixtures as buffer material, considering its response to the thermohydraulic conditions prevailing in a DGR. The relevance of vapor transport during the coupled heat and moisture transfer processes are also analyzed. The study provides a better understanding of the factors influencing the coupled heat and moisture transfer phenomena and sheds light on the long term prediction of the performance of a DGR.