# Study on the Vibration Effects of Cyclic Blasting on Bridge Structures under Construction
## 4 Effect and Optimization of Multiple Blasting Vibrations on Bridges Under Construction
### Optimization and Analysis of Blasting Vibration Scheme  
Numerous factors influence the cyclic damage to structures caused by blasting vibrations. Based on formulas and site conditions, economical, significant, and controllable parameters were selected as research variables, namely, the number of slot holes, the amount of explosive charge in the slot holes, and different delay segments. Four blasting schemes were tested by adjusting the actual field experiment plans: Scheme 1 (hole depth 1.7 m, linear charge density in slot holes 0.33 kg/t), Scheme 2 (hole depth 1.9 m, linear charge density 0.33 kg/t), Scheme 3 (hole depth 1.7 m, linear charge density 0.42 kg/t), and Scheme 4 (hole depth 1.9 m, linear charge density 0.42 kg/t), compared with the original engineering Scheme 3. Scheme 3 corresponds to the blasting scheme illustrated in Figure 3. The maximum vibration velocity peaks generated on the bridge deck by the four blasting schemes were compared to select the optimal construction parameter scheme. The comparison results are shown in Figure 17.  
As shown in Figure 17, Schemes 1 and 2 have the lowest overall peak vibration velocities, while Scheme 4 produces the highest peak vibration velocity on the bridge deck, posing the greatest safety risk. Given that construction should aim for efficiency, with Scheme 1 achieving a penetration rate of 1.7 m per cycle and Scheme 2 achieving 1.9 m per cycle, it is recommended to adopt Scheme 2 (hole depth 1.9 m, linear charge density 0.33 kg/t) for tunnel excavation. The primary distinctions between Scheme 2 and Scheme 3  
Figure 16: Regression relationship between peak particle velocity (PPV) at Point 1 and blasting frequency. Figure 17: Peak vibration velocity of various blasting schemes. lie in two parameters: the depth of the blasting holes and the amount of explosive charge used. All other design aspects remain consistent between the two schemes. Investigating the impact of different segment delays on the bridge deck near the tunnel based on Scheme 2 for tunnel construction, vibration distribution analysis is conducted along the bridge axis, depicting the tri-directional peak vibration velocities at different delayed segments along the bridge deck axis, as illustrated in Figures 18-20. Analysis of Figures 18-20 reveals the following: (1) With increasing blasting delay time, within a lateral distance of 50 m from the blasting point on the bridge deck, the peak transverse vibration velocity decreases rapidly for different delay segments of blasting schemes, followed by a gradual reduction in the differences between various delay segments. It becomes challenging to discern the delay with the lowest vibration impact due to the cross-effect of longitudinal and vertical vibrations, while the maximum peak transverse vibration velocity is observed for the 30 ms delay, which is the numerically highest. (2) Within the range of 50 to 250 m on the bridge deck, the lateral and longitudinal peak vibration velocities for the same instance and monitoring point fluctuate beyond each other for delays of 30 to 40 ms. The longitudinal peak vibration velocity for the 30 ms delay is significantly higher than the other three delay segments, and after 200 m, the peak vibration velocity remains relatively stable. Consequently, delays of 30 and 40 ms have  
Figure 19: Peak longitudinal vibration velocity for Scheme 2. Figure 20: Peak vertical vibration velocity for Scheme 2.  
the highest impact on bridge vibration, with the 50 ms delay exhibiting lower vibration compared to the 60 ms delay. (3) There is little difference in vibration velocity between delays of 50 and 60 ms within the range of 250 to 400 m. (4) A comprehensive comparison of the tri-directional vibration along the bridge axis within the three segments reveals that the maximum peak vibration velocity occurs for the 30 ms delay, while the minimum occurs for delays of 50 and 60 ms.