## 2 Underwater Rock-Plug Blasting Experiments
### Experimental Results and Analysis  
#### 2.3.1 Influence of the Head of Water  
After detonation of the explosive, all block particles in the rock-plug sample were subjected to the blast load (Figure 5). Some block particles on both the upstream and downstream end faces of the rock plug moved outwards along the axis of the rock plug under the blast load. At 11 ms, the block group ejected from the downstream end face of the rock plug moved 100 mm along the axis of the rock plug. The average velocity of the block group flowing out from the downstream end face within 11 ms was calculated to be 11.364 m/s. As the block groups moved further, it was observed that the block group ejected from the upstream end face reached the gradation at 100 mm at 16.5 ms. It was calculated that the average velocity of these blocks within 16.5 ms was 7.576 m/s. At 105.5 ms, most of the block group driven by the blast load from the downstream end face accumulated on the bottom of the downstream water tank; the vertical velocity of the block group in the upstream water tank gradually decelerated to zero under frictional resistance from the water and gravity, and these blocks began to fall. After 105.5 ms, block particles flowing out from the downstream end face of the rock-plug sample moved to the downstream water tank under the actions of scouring and gravity. Within 1026.5 ms of the detonation, water in the upstream water tank descended slowly, indicating that the rock-plug blasting failed to effectively form a through-going channel (Figure 5d).  
The water level in the upstream water tank increased to 205 mm, as shown in Figure 6. At 10.5 ms after the detonation, the block group flowing out from the downstream end face reached 100 mm, so the average motion velocity of the blocks differed only slightly from that under a head of water of 105 mm. At 24 ms, the block group thrown out from the upstream end face reached 100 mm. Compared to the conditions involving a head of water of 105 mm, the average velocity of these blocks decreased to 5.208 m/s with a head of water of 205 mm. Figure 6c shows that the number of blocks driven by water scouring was significantly reduced at 1026.5 ms. Compared to the conditions involving a head of water of 105 mm, significant flows of water could be observed in the downstream water tank with a head of 205 mm, which indicated that the increase in the applied head of water was conducive to improving the degree of penetration of the rock-plug blasting.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Serial Number** & \
\begin{tabular}{c} **The Opening Angle of the** \\ **Rock Plug \(\beta\)/\({}^{c}\)** \\ \end{tabular} &
\begin{tabular}{c} **The Head of Water h/mm** \\ \end{tabular} \\ \hline Case 1 & 30 & 105 \\ Case 2 & 30 & 205 \\ Case 3 & 30 & 305 \\ Case 4 & 40 & 305 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Experimental conditions for underwater rock-plug blasting.  
Figure 5: Process for experimental case 1 (\(\beta=30^{\circ}\), h = 105 mm).  
Figure 7 shows the condition involving a water level of 305 mm in the upstream water tank. The block group driven by the blast load from the upstream end face did not reach the 100 mm gradation until 34.5 ms, so its average velocity was 3.623 m/s. Under the effects of the water scouring, many blocks of particles flowed to the downstream water tank along the rock-plug sample. Comparing Figure 7 with Figure 6c, it can be seen that this took similar amounts of time under the two conditions, but there were more blocks driven by water scouring with a head of water of 305 mm. According to Figure 7c,d and compared to Figures 5d and 7d, the largest water flow to the downstream water tank was found with a head of water of 305 mm. Within the same time period, the water level in the upstream water tank dropped the most rapidly with a head of water of 305 mm, suggesting that this had a better effect on the penetration of the rock-plug than other conditions.