# Numerical Simulation Study of Cavity Formation in Soil under Blast Load
## 3 Numerical Simulation Results and Discussion
### Results of Numerical Simulation  
The simulation setups were basically the same for the different explosives, with a difference in the charge length, which is related to the explosive density used. The lengths were 6 cm for Riogel, 7 cm for Permonex, and 10 cm for Pakaex. The Euler 2D model was applied in a block with the dimensions 300 (j-axis) \(\times\) 400 (i-axis) cm. The cell dimensions were 1 \(\times\) 1 cm, ensuring the same number of cells as the path dimensions. The total number of cells was 120,000. The flow out was encompassed with boundaries in both directions. The stem was represented by sand material with a length of 50 cm. The part dimensions were chosen in a way to assure there was no influence of the blast on the soil material in the distance and reflection at the boundary was prevented. On the other hand, part dimension and the number of cells were chosen so as not to affect the speed of the calculation. The process causes soil to be densified to values near crystal density because all-natural air and water were pressed from that zone and soil particles are arranged and pressed, which is proven in the simulation and field measurements. In a practical manner, the zone with an increased density is the active load zone for the installed anchors. The results of the numerical simulation are presented in Table 5, and the relation of cavity volume with water content for the specific explosives is shown in Figure 4.  
According to the correlation results, it can be concluded that water content can be a reliable predictor when speaking of cavity formations caused by blasting, and that is not a surprising result. Although a very simple geotechnical parameter, water content plays an important role when dealing with soil problems. The amount of water, disposition of water in soil and disposition of the pressures in water, has a huge influence on the soil behavior in terms of loading [17]. The relation of cavity volume with plasticity index for the specific explosives is shown in Figure 5.  
According to the analysis and results displayed in Figure 5, the plasticity index can also be a reliable predictor for the volume of cavity formation. A difference between the volume of the cavity produced by ANFO and also produced by powdered ammonium nitrate explosive is noticed in the case of soil sample S-8. It is a low-plasticity soil with lower water content (17.8%) and a significant amount of sand (17.9%). According to the results, it can be noticed that in soils with a smaller amount of water, with respect to the plasticity index, the ANFO explosive generally produces a bigger cavity than the powdered explosive. The reason may lie in the fact that ANFO explosive produces a slightly bigger volume of gas products (nearly 10%), but for further \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Explosive** & **Cavity Experimental** & **Cavity Model** & **Deviation** \\  & [**dm\({}^{3}\)**]** & [**dm\({}^{3}\)**]** & [**\%**] \\ \hline ANFO (Pakaex) & 752 [15] & 839 [15] & 12.9 [15] \\ Ammonium nitrate powder explosive (Permonex) & 835 & 789 & 6.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Validation results. explanation, it is important to provide more experiments and simulations for soils with similar parameters. It can be generally stated that soils from different locations have similar plasticity index results and the liquid limit has very similar properties, such as stiffness and shear  
Figure 4: The graphical analyses of (**a**) the results of the water content and the volume of cavity depend-ence and (**b**) the correlation between the water content and the volume of cavity. Figure 5: The graphical analyses of (**a**) the results of the plasticity index and the volume of cavity dependence and (**b**) the correlation between the plasticity index and the volume of cavity.