Easer Hole Design Method Based on the Principle of Minimum Burden at the Hole Bottom and Its Application in Tunnel Blasting

Current tunnel blasting hole layouts are mostly designed based on a two-dimensional plane at the workface, without considering the distribution of the minimum burden at the bottom of the blast holes. This results in a significant number of residual holes at the bottom, reducing excavation efficiency. To address this issue, this study proposes an easer hole design method based on the principle of minimum burden at the hole bottom. The method involved the arithmetic distribution for the minimum burden at the bottom of easer holes, using the difficulty of rock breaking as the design principle for hole positioning. Through theoretical analysis, numerical simulation, and field tests, it is proposed that the minimum burden at the bottom of the holes should increase progressively with the initiation sequence, and the relationship between burden distribution and blasting effect was investigated. This study indicates that using the new design principle achieves better blasting results than the model with an evenly distributed burden. When the control ratio of the minimum burden at the bottom of each row of easer holes is 1.3, an average residual hole depth of 36.7 cm and a maximum damage volume of 4.638 m3 can be achieved, yielding the best overall blasting effect. The application of this blasting scheme in the field significantly improved the residual hole problem, reducing the average residual hole depth to 39.5 cm, which is a 43.4% reduction compared to the previous scheme. Additionally, the utilization rate of blast holes in the new scheme increased to 91.3%, an improvement of 11.0% over the previous scheme. This study provides new insights and methods for tunnel blasting hole layout design, offering significant engineering application value.