The presence of water in a borehole could be beneficial for rock breakage performance if the water is thoroughly sealed (Jang et al., 2018). Few studies have examined the positive benefits of water in a borehole on blasting performance. Few studies on water-coupled and water-cushion blasting had been conducted in China for the blasting performance improvement and blasting induced vibration control (Huang & Li, 2015; Yong-chi, 2005).
Effects of rock saturation to blasting damage zone
In general, the stress wave velocity is faster in the saturated rock than the dry rock. In addition, the strength of rock will be decreased when it is saturated (𝑆𝑑𝑟𝑦 ≫ 𝑆𝑠𝑎𝑡). (Kim & Changani, 2016) conducted research to find the effects of water contents on the mechanical strength of rock. The research found that both compressive and tensile strength of saturated rock samples were reduced approximately 20% compared with dry samples in both static and dynamic loading conditions.
(Cui, 2011) conducted research on water-silt composite blasting to substitute the conventional silt stemming blast for tunnelling. The research observed huge wave reflections in the water and the performance of water bubbles and vapour during the rock breaking processes.
Blasting pressure oscillation
Underwater explosions generate oscillating gas bubbles causing cyclic pressure waves, which inflict more structural damage than air explosions. Similar cyclic loading effects have been observed in rocks, leading to strength deterioration—up to 30%—due to microcrack development. Studies show that variable frequency cyclic loading creates more complex microcracks than monotonic loading. (Zhou et al., 2017) found that cyclic pumping during hydraulic fracturing increases rock damage. Although water deck blasting (WDB) differs from underwater explosions, simulations show pressure cycling at the borehole bottom. This cyclic loading in WDB may accelerate rock fracturing by weakening the rock structure.
Energy encapsulation
When an explosive detonates in a blasthole, shock waves rapidly create microcracks and high-pressure gases expand the cracks, pushing rock fragments. Only 7–25% of the explosive energy contributes to effective rock breakage, while up to 60% is lost as heat and deformation (Holmberg, 2003; Sanchidrián et al., 2007). Improving energy retention enhances blasting efficiency. Needham’s experiment showed that a snow layer encapsulates blast energy, increasing overpressure due to impedance mismatch. Similarly, in Water Deck Blasting (WDB), the water layer at the hole’s bottom slows energy transmission and extends its action on surrounding rock. This energy encapsulation improves fragmentation performance.
Reference
Cui, Z.-D. (2011). Effect of water–silt composite blasting on the stability of rocks surrounding a tunnel. Bulletin of Engineering Geology and the Environment, 70(4), 657–664. https://doi.org/10.1007/s10064-010-0346-3
Holmberg, R. (Ed.). (2003). Explosives and Blasting Technique: Proceedings of the EFEE 2nd World Conference, Prague, Czech Republic, 10-12 September 2003. Taylor & Francis. https://doi.org/10.1201/9781439833476
Huang, B., & Li, P. (2015). Experimental Investigation on the Basic Law of the Fracture Spatial Morphology for Water Pressure Blasting in a Drillhole Under True Triaxial Stress. Rock Mechanics and Rock Engineering, 48(4), 1699–1709. https://doi.org/10.1007/s00603-014-0649-y
Jang, H., Handel, D., Ko, Y., Yang, H.-S., & Miedecke, J. (2018). Effects of water deck on rock blasting performance. International Journal of Rock Mechanics and Mining Sciences, 112, 77–83. https://doi.org/10.1016/j.ijrmms.2018.09.006
Kim, E., & Changani, H. (2016). Effect of water saturation and loading rate on the mechanical properties of Red and Buff Sandstones. International Journal of Rock Mechanics and Mining Sciences, 88, 23–28. https://doi.org/10.1016/j.ijrmms.2016.07.005
Sanchidrián, J. A., Segarra, P., & López, L. M. (2007). Energy components in rock blasting. International Journal of Rock Mechanics and Mining Sciences, 44(1), 130–147. https://doi.org/10.1016/j.ijrmms.2006.05.002
Yong-chi, L. (2005). Numerical simulation on effects of radial water-decoupling coefficient in engineering blast. Rock and Soil Mechanics. https://www.semanticscholar.org/paper/Numerical-simulation-on-effects-of-radial-in-blast-Yong-chi/5ed500da17d0b8c1a3da929208c8cc579c440423
Zhou, Z.-L., Zhang, G.-Q., Dong, H.-R., Liu, Z.-B., & Nie, Y.-X. (2017). Creating a network of hydraulic fractures by cyclic pumping. International Journal of Rock Mechanics and Mining Sciences, 97, 52–63. https://doi.org/10.1016/j.ijrmms.2017.06.009
