Delay blasting reduces blast-induced vibrations through a controlled timing mechanism that manages the sequence of detonations.
Mechanism of Vibration Reduction
Staggered Detonation
By using delay detonators, explosions are initiated at staggered intervals rather than simultaneously. This staggered timing allows the seismic waves generated by each blast to propagate separately, reducing the cumulative energy that reaches the surrounding ground.
Interference of Seismic Waves
When blasts are timed apart, the resulting seismic waves can interfere with each other. This interference can lead to destructive interference, where the waves cancel each other out to some extent, thereby lowering the peak vibration levels experienced at monitoring points.
Controlled Energy Release
The timing of the delays can be optimized to control the energy release from each blast. Shorter delays can lead to a more efficient fragmentation of rock while minimizing the intensity of vibrations. Studies have shown that using optimal delay times (around 16-20 milliseconds) can significantly reduce vibration intensity, sometimes by as much as 69.7% in close proximity to the blast area.
Distance Effect
The reduction in vibration intensity is also influenced by the distance from the blast site. As the distance increases, the effect of the staggered detonations continues to mitigate vibrations, demonstrating that delay blasting can maintain lower vibration levels even at greater distances from the blast.
Frequency Control
Delay blasting can also help in managing the frequency of the vibrations. The main frequency associated with blasting vibrations typically remains within a certain range, and the use of delays can prevent abrupt changes in this frequency, which is vital for protecting nearby structures that may be sensitive to specific vibration frequencies.
Conclusion
To sum up, delay blasting effectively reduces blast-induced vibrations through staggered detonations that allow for better control of seismic wave propagation and energy release. This technique not only minimizes the impact on surrounding structures but also enhances the overall efficiency of the blasting operation.
Bibliography
Qiu, X., Shi, X., Gou, Y., Zhou, J., Chen, H., & Huo, X. (2018). Short-delay blasting with single free surface: Results of experimental tests. Tunnelling and Underground Space Technology, 74, 119–130. https://doi.org/10.1016/j.tust.2018.01.014
Shi, X. Z., & Chen, SH. R. (2011). Delay time optimization in blasting operations for mitigating the vibration-effects on final pit walls’ stability. Soil Dynamics and Earthquake Engineering, 31(8), 1154–1158. https://doi.org/10.1016/j.soildyn.2011.04.004
Yang, J. H., Lu, W. B., Jiang, Q. H., Yao, C., & Zhou, C. B. (2016). Frequency comparison of blast-induced vibration per delay for the full-face millisecond delay blasting in underground opening excavation. Tunnelling and Underground Space Technology, 51, 189–201. https://doi.org/10.1016/j.tust.2015.10.036