During underground powerhouses blasting excavation, extended inter-hole delay times are commonly employed to safeguard critical structures like rock-anchored beams by preventing blast vibration peak superposition. This method, however, results in elevated boulder rates. To address this issue, vibration control and fragmentation optimization studies were conducted using millisecond blasting techniques. Using the linear superposition principle for blast vibrations, this study established a vibration amplification factor model that incorporates the number of holes and rock mass attenuation properties, and derived a computational formula for critical inter-hole delay times that meet vibration safety thresholds at varying distances. Field validation tests were conducted during the excavation of Xulong Hydropower Station′s underground powerhouse, confirming the theoretical model′s practical applicability. Results demonstrate that the optimized 50 ms inter-hole delay scheme, compared to the conventional 100 ms approach, maintains peak particle velocity at rock-anchored beam benches below 2.8 cm/s while achieving superior fragmentation performance. This configuration reduces the median fragment size from approximately 75.5 cm to 11.3 cm, significantly improving size-distribution uniformity and effectively minimizing boulder occurrence. The research establishes both theoretical foundations and practical methodologies for determining critical delay intervals to reconcile vibration safety and fragmentation quality in underground blasting operations.

The stability calculation is the key to prevent and control the geological disaster of dangerous rock collapse, which is of great practical and prediction significance. However, the quasi-static method cannot depict the influence of factors as the shape and geometric size of the dangerous rock mass, the frequency and initial phase on the actual blasting vibration load. Based on conventional pseudo-static analysis and the slice method, a blasting dynamic stability analysis method considering size effect is established. This calculation program is compiled by using MATLAB. The results indicate that the calculated minimum stability coefficients of dangerous rock mass vary periodically with the initial phase of the blasting seismic waves. For a given calculation with specific parameters, the coefficients are proximate to those calculated by conventional quasi-static analysis. The relative difference of these two calculations is between 5.1% and 8.2%, which indicates the calculation method and program are reasonable and effective. When the number of slices is 1, the calculated results of the program are equivalent to those calculated by traditional quasi-static method. The method proposed in this study provides a reference for dynamic stability analysis and evaluation for dangerous rock mass.

The drilling and blasting method is widely used in tunnel excavation. Typically, smooth blasting can meet the quality formation requirements. However, achieving ideal contour control blasting effects and ensuring the safety and stability of surrounding rock mass are challenging due to limitations in drilling conditions and charging in small section tunnels, especially when encountering adverse geological conditions. This often results in increased costs for subsequent support and lining. To address these issues, on-site blasting tests were conducted based on small-section hydraulic tunnels to explore applying energy-gathering hydraulic blasting technology to improve blasting parameters in poor geological conditions. The main conclusions from analyzing and evaluating the quality of contour excavation using 3D laser scanning technology are as follows:(1)The results indicate that shaped charge blasting can reduce over-excavation and under-excavation by 40.8% and 54.2%, respectively, compared to conventional blasting under the same geological conditions. (2)A comparative analysis of blasting results under different borehole arrangements shows that no boreholes are needed to connect the arch crown and the side wall. Utilizing the shaped charge effect to control can reduce over-excavation at the arch shoulder. (3)In fourth-class surrounding rock mass, including silty mudstone and stratified sandstone, the smoothness of the wall surface is less affected by blasting parameters and is promarily determined by lithology. Moreover, the smoothness of stratified sandstone can be improved by more than 30% compared to silty mudstone. In summary, the reasonable application of shaped charge water pressure blasting technology in small cross-section hydraulic tunnels can improve tunnel wall shaping under smooth blasting conditions.

The geological structure of the Ying Liang-bao hydroelectric underground power-house is complex due to the development of surrounding rock fissures, messy lithology, and a rock body with "hard, broken, miscellaneous" characteristics. Excavation and molding pose difficulties while pre-splitting blasting has poor effects. To address this issue, we conducted a systematic blasting test combined with pre-splitting for central groove construction on layer III of the power-house. In initial tests, both sides of the wall exhibited significant breakage after blasting and traces of pre-splitting holes were not clearly visible when linear charge density was nearly 100 g/m lower than standardized calculation values. Acoustic testing data revealed that average longitudinal wave velocity in the rock mass body was 4.03 km/s indicating overall poor integrity. Additionally, segmental wave velocities along axial depths from 0~1.5 m, 1.5~3.9 m and 3.9~7.4 m were found to be 2.59 km/s, 3.58 km/s and 4.70 km/s respectively suggesting segmented integrity differences in depth direction. Based on these findings an average single-hole linear charge density for pre-splitting blasts during excavation was determined to be between 0.123~0.284 kg/m with different densities selected according to varying depths while small charge rolls were evenly spaced for each section. The results obtained through testing and application have been positive ensuring basic formation of wall surfaces while significantly increasing half-porosity levels.