## 4 Results and Discussion  
### Rock-Damaging Effects of Different Interval Medium  
Conventional faceted blasting uses air as the interval medium. In soft rock tunnel blasting with developed joints and fissures, the explosive gas will leak quickly, resulting in poor blasting results. To address this issue, we maintain the interval charge structure by replacing air with water as the medium. Leveraging the incompressibility of water and its high flow viscosity, we aim to enhance the blasting effect. Figure 4 shows the charging structure. The detonation position was at the bottom of the lower explosive, and 0 ms detonation time was set by the keyword *INITIAL-DETOTION. The blast stress wave propagates from the bottom of the hole to the free surface in about 0.6 ms. Figure 5 shows the damaged cloud at that moment; rocks fracture at damage factors more than 0.75 and appear orange \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Unit** & **Value** \\ \hline Density, \(\rho\) & kg/m\({}^{3}\) & 2010 \\ Shear modulus, G & GPa & 5.6 \\ Normalized cohesive strength, A & & 0.32 \\ Normalized pressure hardening, B & & 1.76 \\ Strain rate coefficient, C & & 0.0127 \\ Pressure hardening exponent, N & & 0.79 \\ Maximum tensile hydrostatic pressure, T & MPa & 7.63 \\ Quasi-static uniaxial compressive strength, fc & MPa & 33.7 \\ Quasi-static threshold strain rate, EPS0 & s\({}^{-1}\) & 1 \\ Amount of plastic strain before fracture, EFMIN & & 0.01 \\ Normalized maximum strength, SFMAX & & 7 \\ Crushing pressure, Perush & MPa & 25.38 \\ Crushing volumetric strain, \(\mu\)crush & & 0.00167 \\ Locking pressure, Plock & GPa & 0.8 \\ Locking volumetric strain, \(\mu\)lock & & 0.08 \\ Damage constant, D1 & & 0.04 \\ Damage constant, D2 & & 1 \\ Pressure constant, K1 & GPa & 81 \\ Pressure constant, K2 & GPa & \(-\)91 \\ Pressure constant, K3 & GPa & 89 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: HJC model parameters for sandstone [35]. and red on the damage cloud map. While the precise location of the boundary between the crushing zone and the fracture area remains uncertain, a reasonable range can be identified. In this simulation, the ratio of the width of the crushing zone to the radius of the explosives is approximately 6, aligning with the findings of the experimental study conducted by [PERSON] et al. [38]. This consistency lends credibility to the reliability of the simulation results. As can be seen from Figure 5, under the air interval charge condition, the damage to the surrounding rock caused by the stress wave in the air section is rapidly reduced. The damage variable in the central air section is about 0.5, with a length of about 26 cm, and the rock is in a fractured but not peeling state. Under the water interval charge condition, the uniformity of damage distribution is greatly improved with the water-spaced charge. The position of the water interval still shows a significant range of damage, with an overall increase in damage area of approximately 25.6 percent and a notable increase in energy utilization. To analyze the damage of the rock around the borehole, Unit I was taken as the monitoring reference unit, and one monitoring unit was taken every 10 cm down the axis of the borehole, with a total of 20 units. Extract the peak tensile stress \(\sigma_{tmax}\) for 8 units in the PT partition. To study the variation relationship between \(\sigma_{tmax}\) and \(D_{\max}\) in PT partition and to assess the reasonableness of partition boundary delineation, this paper extracts the peak value of the damage variable \(D_{max}\) values for all the monitoring units. Figure 6 shows the variation of \(\sigma_{tmax}\) and \(D_{max}\) with the depth of the borehole. Figure 4: Model charge structure. Figure 5: Rock damage range around the blast hole at 0.6 ms.  
Figure 6: Variation of \(\sigma_{tmax}\) and \(D_{max}\) with depth of blasthole: (**a**) the variation curve of \(\sigma_{tmax}\), (**b**) the variation curve of \(D_{max}\).