The significant size of blasting blocks in super-large cross-section hard rock caverns will have a profound impact on blasting construction efficiency and process connectivity. Engineering practice has demonstrated that the horizontal structural planes within the rock are among the primary factors contributing to the large blasting block size in hard rock caverns. To investigate the mechanism by which the horizontal structure of a hard rock mass affects the propagation of blasting energy, a hole layout optimization method tailored for complex jointed rock masses is proposed. Using the blasting construction of the middle step in a specific super-large hard rock chamber with a particular cross-section as the engineering background, a three-dimensional blasting model of the rock mass with horizontal joints is established through numerical simulation, based on the RHT model. The LS-DYNA finite element analysis software was employed to elucidate the coupling mechanism between structural planes and blasting energy, as well as the influence of hole distribution patterns on block size distribution. The results indicate that blasting-induced damage and fractures preferentially propagate along the weak surface of the structure. The reflection and superposition of stress waves at the structural surface facilitate the preferential development of radial fractures along vertical or nearvertical structural planes, thereby delaying energy release. The plum blossom-shaped hole distribution ensures more uniform energy distribution through multi-directional stress interference, inhibiting the formation of dominant through-fractures and resulting in a honeycomb-like fracture structure. This effectively reduces the incidence of blasting large blocks and significantly enhances the uniformity of block size distribution. Finally, the validity and feasibility of the conclusion were confirmed through field tests. This study offers a theoretical foundation and practical guidance for controlling the blasting block size in hard rock masses characterized by prominent horizontal structural planes.

To mitigate blasting vibration during the excavation of a drainage tunnel located 2.30~3.10 m beneath an existing tunnel, an optimized blasting scheme using millisecond blasting by electronic detonators and a subsection in blasting holes was implemented. The field blasting scheme was initially adjusted based on the conventional blasting situation near the existing tunnel. This involved optimizing hole position parameters and reducing the number of holes. Before the formal blasting in the underpass section, a single-hole blasting test was then conducted near the excavation face to capture the vibration waveform and geological information. Using the linear superposition method, the vibration waveform of various delay intervals was analyzed to select the optimal delay interval. To further improve blasting performance and reduce the vibration of the cut blasting, the first blasting in the cut area was performed by using the subsection blasting in the hole. Field tests and calculations determined that the optimal delay times were 5 ms for the same row of cut holes or spreader holes, 40 ms between rows, and 3 ms for contour holes. The new blasting scheme was implemented and optimized in the field. When the drainage tunnel was excavated at a footage of 1.5 m through the existing tunnel, the maximum vibration of the road surface monitoring point at a distance of 3.10 m directly above was maintained below 4.0 cm/s, ensuring structure safety. Using electronic detonators for precise initiation and sectional blasting successfully controlled site vibration, protected adjacent structures, and provided valuable insights for similar future projects.