Optimization of the matching relationship between the stemming length and minimum burden in cut blasting of large-diameter long-hole stopes

Cut blasting, in which new surfaces and relief space for subsequent blasting are created, is one of the most critical steps in the establishment of large-diameter long-hole (LDL) stopes. To reduce the damage to the chamber roof caused by stemming recoil and improve the rock breaking effect, 15 groups of small-scale model tests with minimum burdens of 3, 4, 5, 6, and 7 cm and stemming lengths of 0, 2, 4, 5, 6, and 7 cm were designed to optimize the matching relationship between the stemming length and minimum burden. First, through the model tests, values were obtained for ten evaluation indexes related to the total mass of fragments, crate size, fragment size, fragmentation energy consumption, and stemming recoil area. Then, the normal cloud combination weighting method was used to combine six subjective and objective weighting methods, and combined weights were obtained. Finally, the test schemes were optimized according to the Euclidean distance and similarity. The test results showed that the best blasting scheme involves a burden of 5 cm and a stemming length of 5 cm, followed by that involving a burden of 4 cm and a stemming length of 4 cm, and the optimal stemming length is approximately equal to the minimum burden. A field test of LDL stope cut blasting was conducted, with a stemming length of 2.2 m and a minimum burden of 2.2 m in the boreholes. The highly satisfactory field blasting effect indicates that the stemming length and minimum burden are reasonable. Ten indexes were obtained and normalized for each of the eight test schemes. Six weighting methods were used to obtain the respective weights, and the normal cloud combination weighting method was used to obtain more reasonable weights.The optimal scheme was that involving a burden of 5 cm and a stemming length of 5 cm, followed by that involving a burden of 4 cm and a stemming length of 4 cm. The optimal stemming length was approximately equal to the minimum burden.An on-site cut blasting test was conducted of the N10#S stope in the Fankou Mine. The upper part of the explosive packs exhibited a stemming length of 2.2 m, and the lower part exhibited a burden of 2.2 m. The highly favorable field blasting effect proves that the above stemming length and minimum burden are reasonable.