Abstract: In order to study the effect of different stemming materials and stemming lengths on the burn cut blasting of hard rock tunnels，based on engineering examples，a three-dimensional numerical model was established using ANSYS/LS-DYNA simulation software to compare and analyze five different blockage conditions. Based on the numerical model calculation results，qualitative analysis was conducted on the expansion of blasting cracks in the cutting area，and quantitative analysis was conducted on the stress situation of typical rock parts. The results indicate that，firstly，the free surface rock is mainly subjected to tensile stress to generate cracks，and the blockage of the blast hole prolongs the overall action time of the explosion load，resulting in a denser number of cracks on the free surface. Secondly，the surrounding rock near the air section between the explosive and the stemming material is first crushed by the explosive stress wave and then subjected to multiple transformations between tensile and compressive stresses，causing the crack to be amplified. Due to the ″ gas wedge″ effect of the explosive gas，the crack almost penetrates the model cross-section. Thirdly，after the blockage of the blast hole，the stress value of the explosive gas acting on the rocks around the explosive section is significantly increased，which is 1. 31 - 2. 34 times higher than the peak stress of the rock around the explosive section when it is not blocked. The blockage of the blast hole increases the compressive stress value of the explosive gas when it continues to play a stable role by 3. 70 - 4. 70 times. Finally，when using gun mud and water as blockage materials，the rock-breaking effect of a burn cut with a stemming length of 40 cm is better than that of a burn cut with a stemming length of 60 cm. The research results can provide a theoretical basis for optimizing the parameters of burn-cut blasting in hard rock tunnels.

Key words: drilling and blasting method, hard rock tunnel, burn cut, blast-hole stemming, numerical simulation