Analysis of Causes of Vibration Differences Induced by Different Kinds of Blastholes Based on the Interpretation of Blasting Parameters: A Case Study in Dam Foundation Excavation

The vibration characteristics induced by different kinds of blastholes, such as presplitting blastholes, smooth blastholes, and production blastholes, are quite different. Figuring out the vibration differences of different kinds of blastholes and the inherent causes are of great significance for the safety control of blast vibration. In this study, taking the excavation of a dam foundation as a case study, the inherent causes of vibration differences induced by presplitting blastholes, smooth blastholes, and production blastholes are investigated and discussed with both theoretical analyses and numerical simulation methods. In addition, onsite blasting experiments are conducted to verify the vibration characteristics differences. The results show that the explosion pressure applied on the hole wall of the presplitting and smooth blastholes are much smaller than those applied on the production blastholes. Thus, the inner blasting effects (i.e., the rock breakage and plastic zone around the blasthole) of the presplitting and smooth blastholes are relatively weaker. On the other hand, the outer blasting effects (i.e., the rock breakage induced by the reflection of blast waves at the free surface) of the presplitting blasthole are negligible because of their substantially larger burden thicknesses relative to the other blastholes. Therefore, much more explosion energy of the presplitting blasthole is converted into vibration energy than the other two kinds of blastholes. However, the vibration energy conversion and the plastic zone development of the smooth blastholes and production blastholes are approximately at the same level due to the balance of their inner and outer blasting effects. The measured peak particle velocities (PPVs) and dominant frequencies induced by different kinds of blastholes show good agreement with the above theoretical and numerical conclusions. It can be drawn that the inherent causes of the vibration characteristics differences induced by various blastholes lie in the differences in the blasting parameters, which determine the proportions of the inner and outer blasting effects.