# Numerical Simulation Study of Cavity Formation in Soil under Blast Load
## 3 Numerical Simulation Results and Discussion
### Results of Numerical Simulation
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Field Designation of Soil**} & \multicolumn{2}{c}{**ANFO**} & **Ammonium Nitrate Powdered Explosive** \\ \cline{2-3}  & **Volume of Cavity** & **Volume of Cavity** \\  & **[dm\({}^{3}\)]** & **[dm\({}^{3}\)]** \\ \hline S-1 & 863 & 787 \\ S-2 & 1112 & 1917 \\ S-3 & 300 & 291 \\ S-4 & 378 & 356 \\ S-5 & 1033 & 868 \\ S-6 & 1095 & 1027 \\ S-7 & 655 & 572 \\ S-8 & 4333 & 2202 \\ S-9 & 2377 & 2304 \\ S-10 & 1790 & 1193 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Numerical simulation results. strength [17]. In that manner, the plasticity index can also be a reliable predictor for volume of cavity in soil caused by blasting. The results of statistical analyses showed a good agreement between volume of cavity and basic geotechnical parameters: water content (w\({}_{0}\)) and plasticity index (I\({}_{\text{P}}\)). A simulation was also performed on the water gel explosive for the S-1 type of soil. The results showed a similar cavity formation for all three types of non-ideal explosives (ANFO, ammonium nitrate, and water gel explosive). The results are presented in Table 6 and in Figure 6. The dimensions of the cavity shown in Figure 6 were determined by digitalization using the open-source Engauge Digitizer Software [18]. The studied non-ideal explosives with different theoretical and experimental parameters showed a similar volume of cavity value with a similar charge mass. It can be concluded that in conditions of soil, the charge mass is crucial, opposite to detonation velocity (VOD) or detonation (borehole) pressure and detonation energy or specific volume of gasses. On the other hand, some dissipation of volume results exist in the range of circa 10%. This indicates that dissipation can be assigned to the measurement uncertainty of the experimental volume measurement method and the non-ideality of the applied explosive. Since the mechanical strengths of soils are significantly lower than the stresses produced by the pressures of the expansion gasses applied by explosives, the differences in cavity volume for the concerned explosives' mass are not influenced by the level of the VOD or the applied pressure of those explosives, and the differences in volume are minor. After equilibrium is reached in the surrounding soil, the remaining energy is used to elongate the stem area. So, according to the simulation and performed test, the main parameters that influence the cavity volume are charge mass, soil moisture content, and plasticity. The shape of the cavity depends on the charge position, or elongation of the a priori borehole, and corresponds well with the direction of the detonation wave propagation related to the charge axle. In that manner, the elongated shape of the cavity is related to the detonation pressure, and the total cavity volume is related to the charge mass and total liberated energy. The experimental results show that the difference in the volume of the cavity produced by the ANFO and the powdered explosive is not significantly different and differs in the order of 10% (752 and 835 dm\({}^{3}\)) from the observed cavities with the same charge mass of 1.0 kg. It can also be seen that the type of explosive has an influence on the shape of the cavity, with the ANFO explosive producing a larger diameter cavity and the AN powder explosive producing a relatively larger deepening. This may be related to the difference between the impact component and the expansion component of the work ability of the explosive, i.e., the higher pressure of the powdered AN explosive compared to the ANFO. With ANFO explosives, the delayed reactions behind the sonic point still release energy and affect the expansion before venting the gasses through the stem zone. The total cavity volume for equal masses of the applied explosive type does not differ significantly. For non-ideal explosives, it can be concluded that the most important parameter is the mass of the explosive, while the detonation pressure, detonation velocity, and gas volume are less important.