## 3 Results and Discussions  
### Effect of Sand-Tire Shred Mixture on Peak Blast Pressure  
A 6-m-thick layer of the mixture of 30% shred tire (rubber) and 70% sand is modeled and investigated to determine the effect of the mixture layer on the blast-induced vibration parameters compared with the response of pure sand. Table 5 includes the dimensions of the blast-induced crater under different explosion charge weights. The sand-tire shred mixtures effectively reduce the diameter of the blast-induced crater in all scenarios. The crater's depth is also decreased by the presence of the mixture layer, except under the 5000 kg explosion charge. The reduced weight of the mixture compared with the sand is believed to be the leading cause of this anomaly. The high-energy explosion, in direct contact with the lightweight mixture layer, forms a deep crater before this layer can dissipate the blast energy.  
Figure 3 presents the simulation results in terms of peak blast pressure at different depths under charge weight explosion scenarios. The results indicate that the sand-tire shred mixture contributes to a significant reduction of peak blast pressure. It is worth noting that peak blast pressure data are only available at depths below the base of the craters (see Table 5). The most significant reduction is 90%, which was achieved at a depth of 2 m under a 100 kg charge, followed by an 84% reduction at a depth of 3 m under a 1000 kg charge, an 83% reduction at a depth of 3 m under a 500 kg charge, and a reduction of 23.6% at a depth of 11 m under a 5000 kg charge. The peak blast pressure reduction at the base of the mixture layers--6 m below the surface--under the surface explosion charges of 100, 500, and 1000 kg was 63%, 63%, and 61%, respectively. Due to the extension of the crater to a depth of 7.8 m below a 5000 kg charge, the first peak blast pressure data for this mixture layer were available at a depth of 8 m below the surface, showing a reduction of 23% compared with pure sand.  
Figure 2: Results of numerical model simulation in ABAQUS software: (**a**) model before the explosion; and (**b**) blast-induced crater after the explosion; and (**c**) time history of blast pressure at a depth of 10 m.  
\begin{table}
\begin{tabular}{c} **Sand–Tire** \\ **Shred Mixture** \\ \end{tabular} \\ \hline
100 & 1.1 & 0.6 & 6.1 & 1.8 \\
500 & 2.3 & 1.8 & 9.9 & 2.5 \\
1000 & 2.9 & 2.4 & 17.75 & 9.9 \\
5000 & 6.5 & 7.8 & 33.4 & 24.6 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Dimensions of the blast-induced crater.  
These results indicate that peak blast pressure decreased with depth for pure sand and the mixture layer. Although the effect of the mixture layer in reducing the peak blast pressure lessens by depth, it is still notably more significant than pure sand at the maximum depth of analysis (12 m under the surface). The peak blast pressure reductions recorded at this depth for the mixture layer compared with pure sand were 58%, 58%, 54%, and 24% under surface charges of 100, 500, 1000, and 5000 kg, respectively. A noteworthy point in the results is a sudden increase in peak blast pressure at the base of the mixture layers, as shown in Figure 3a-c. Equation (5) states that soil density directly impacts the peak pressure; therefore, this increase at the interface of two layers is due to the higher density of sand in the mixture layer.