Quantitative analysis of surrounding rock damage induced by different blast hole types in drift blasting

To quantify the impact of blast hole types on drift surrounding rock damage, on-site sequential blasting tests were conducted in the slightly weathered gabbro. High-frequency ground-penetrating radar (GPR) measured sidewall damage after cut, auxiliary, and contour hole blasting, obtaining their damage contribution data. To acquire damage data at all typical locations, a 3D LS-DYNA numerical model for sequential blasting-induced damage was established. Model reliability was verified by GPR data. Since rock mass damage in numerical simulations is typically characterized by a damage factor (which can take on multiple values), a correlation was established between the measured damage and the values of this factor obtained from the simulations. Cumulative damage characteristics and evolution laws at different locations were revealed. Results show: 1) GPR-measured damage depth matches the simulated depth at a damage factor of 0.3, set as the rock mass damage threshold. 2) Surrounding rock damage depth at the hole bottom plane is 55.7%–63.7% of that at the hole collar plane, with severe damage depth accounting for 58.4% and 70.2% of the two planes, respectively. 3) Within 0.8 m from the hole collar, sidewall damage is caused by the combined action of auxiliary and contour holes, with auxiliary holes’ contribution reaching a maximum of 37.1%; between 0.8 and 1.08 m, the contribution of auxiliary holes decreases, and damage becomes dominated by contour holes; beyond 1.08 m, damage is primarily attributable to contour holes. Vault damage is primarily induced by contour holes, while floor damage is caused by cut and bottom holes, with the maximum cut hole contribution at 22.1%. The findings provide references for surrounding rock damage control and blast hole parameter optimization in the slightly weathered gabbro.