## 2 Materials and Methods
### Soil Details and Predictions  
To investigate the effect of soil particle mineralogy, carbonate sand was chosen as it is predominantly made up of plate-like particles, in stark contrast to the more spherical quartz-based sands tested previously [17; 25; 26; 27]. Figure 2 shows electron microscopy of the two sands used in this work at different levels of magnification. Previous work [7] conducted testing on three sizes of quartz-based Leighton Buzzard (LB) sand. The three sizes used were LB Fraction B (hereafter referred to as LB); 2 LB, which is approximately double the size of LB Fraction B; and LBF, which is a better graded sand sized between LB and 2 LB. [PERSON] et al. [7] found that small changes in particle size within this range did not result in differences in total impulse; therefore, any changes in loading observed in the current work with sand of similar sizes can be attributed to other factors. In this study, we define carbonate sand as having greater than 50% calcium carbonate content. Soils with less than 50% calcium carbonate are known as calcareous soils. Due to the large quantities of sand required for blast testing, a sustainable source of sand of the correct particle size distribution (and mineralogy) was required. The material used was aquarium sand manufactured from sea washed shells (calcium carbonate) produced by Tropical Marine Centre. Tropical Marine Centre's 'EcoSand Fine' was found to be the most suitable as it has a particle size distribution between fractions of Leighton Buzzard sand used in previous testing that were shown not to have a notable effect on impulse [7]. The bulk density of the carbonate sand was measured to be 1.27 Mg/m\({}^{3}\) (\(w=5\%\)), which is considerably lower than the density of 1.67 Mg/m\({}^{3}\) (\(w=5\%\)) measured for LB (\(G_{\rm s}=2.65\), \(\rho_{dmin}=1.48\) Mg/m\({}^{3}\), \(\rho_{dmax}=1.74\) Mg/m\({}^{3}\) and \(D_{r}=73\%\)). It is well known that the intraparticle voids play a large role in the reduced bulk densities seen in carbonate sands, leading to an expected range of 1.15-1.5 Mg/m\({}^{3}\)[16]. The minimum and maximum densities were 1.04 and 1.31 Mg/m\({}^{3}\), respectively, giving a relative density \(D_{r}=85\%\). The specific gravity is 2.73, being slightly higher than that for LB. Figure 2: Electron microscope images of the two types of sand tested: the left-hand images show the difference in particle shapes and the right-hand images show the difference in surface texture of the particles. It has been shown in previous work that increasing bulk density led to an increased measured impulse but that moisture content had a greater effect increasing impulse than the added mass alone would suggest [11]. This led to the development of a modification to the Westine model [2] to determine the loading from a buried charge [7]. The Westine model quantifies the soil based on its bulk density alone, whereas the [PERSON] et al. [7] model extends this to include moisture content. Equation (1) gives the formulation of the [PERSON] et al. model, which determines the impulse relative to the baseline condition of dry (0% moisture content) quartz sand at a bulk density of 1.6 Mg/m\({}^{3}\). In previous work, a lower bound of 1.6 Mg/m\({}^{3}\) for moisture content was deemed acceptable due to the minimum densities achievable in silica-based soils. \[I_{mod}=0.9-0.096w+0.033\rho+0.078w\rho \tag{1}\]  
where \(w\) is the gravimetric moisture content (%) and \(\rho\) is the soil bulk density (Mg/m\({}^{3}\)). Equation (1) has been rounded to 2 significant figures here as the extra precision makes no practical difference to predictions. This model predicts that, for two soils with the same moisture content and comparable particle size distribution to the baseline, the one with a higher bulk density will result in a larger loading. In addition, it predicts that, for soils with a bulk density above 1.23 Mg/m\({}^{3}\), increasing the moisture content also increases the loading.