## 4 Discussion and Conclusions  
Table 4 summarises both the experimental results, and the output from the empirical models. This shows that, relative to the 2.5% moisture content quartz sand, carbonate sand is predicted to produce lower loading due to the lower bulk density. In contrast, the experimental results show an increase over the quartz sand baseline. Combining the measured increase and the predicted decrease, this indicates that a balance of factors affecting the loading is incorrect in previous models [2,7]. In the case of carbonate sand at 7.5% moisture content, this additional factor accounts for an 11.6% increase over what is predicted from previous work [7], indicating that there is an overdependence on the role of bulk density in previous models. This assumption is supported by work on explosives buried in materials other than soils [17,34], where charges submerged in water showed no decrease in impulse, nor did those within saturated lead shot [34], where again, despite the increased bulk density, the measured impulse was comparable with that in saturated sand. Particle mineralogy and, hence, the role of particle breakage have not previously been investigated. The low degree of breakage seen can be explained to a certain degree by [PERSON] et al. [13], who found that the extent of particle breakage was higher under quasi-static loading than under dynamic loading conditions at the same stress. The quartz-based sands in this paper were more friable than the similarly sized carbonate sands, which is in contrast to the published literature but is possibly a product of the artificial nature of the sand tested and that the quartz sand was more uniform [15]. However, the results suggest that the \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Series** & **Measured** & **Westine Prediction** & **Imod Prediction** \\ \hline LB 2.5\% & Baseline & Baseline & Baseline \\ LB 5.0\% & 0.8\% & 1.1\% & 9.31\% \\ Carb 2.5\% & 0.7\% & \(-\)12.2\% & \(-\)8.4\% \\ Carb 5.0\% & 3.8\% & \(-\)12.0\% & \(-\)6.6\% \\ Carb 7.5\% & 7.8\% & \(-\)10.6\% & \(-\)3.7\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Difference in measured and predicted total impulse relative to the 2.5% LB series. Figure 8: Total interpolated impulse within the 100 mm instrumented region for each test, with the average for each series overlaid as a dashed line. reduction in particle breakage could have an impact on the overall impulse delivered to the target, with the lower degree of particle breakage in the carbonate sands correlating with the increase in impulse over the quartz sands. However, this is very much a second-order process due to the small variations observed. The dynamic compaction response of the two sands could also be a cause for variations in impulse. Testing by [PERSON] and [PERSON] [35] has shown that, in dynamic testing, the stiffness of the carbonate sand is lower than that of the quartz sands and that this is also a product of the moisture content of the sand, as seen previously [36]. It is known that the plate-like particles of carbonate sands likely produce soils with greater shear strength at low stresses [15; 16]. At higher stresses, the authors of [35] indicated little difference between the two soils at higher degrees of compression. Whether this behaviour has an impact at the high stresses seen in blast events is as yet unknown but will be the focus of future research. To conclude, this work has found the following:  
* There is no substantial difference in the total impulse and specific impulse distribution between charges buried in quartz and carbonate sand;
* There is no increase in the observed particle breakage for carbonate sand over quartz sand during buried charge testing. Moreover, there is a small observed increase in breakage of quartz sand over carbonate sand. Conceptualisation, T.L. and S.C.; methodology, T.L. and S.C.; formal analysis, T.L. and R.W. ; writing--original draft preparation, T.L. ; writing--review and editing, S.C., R.W., S.R., M.G. and I.E. ; supervision, S.C. and S.R.