## 4 Results and Discussion
### Using Laboratory Results to Predict Parameters Found for Field Tests (at 250% Scale)
#### 4.4.2 Comparing Experimental Values between Field and Laboratory Tests  
To estimate the equivalent blast parameters at a 250% geometric scale, the mean time-based blast parameters (time of arrival, positive phase duration, and impulse) obtained from the 75% and 100% scale tests were multiplied by the factor (1/K). In this case, K is the geometric scale factor, which equates to 3.33 (K = 0.3) for the 75% scale and 2.5 (K = 0.4) for the 100% scale. By applying this scaling factor, the corresponding blast parameters at the 250% geometric scale can be calculated. The predicted values based on the mean values (refer to Table 3), along with the Gajewski and Sielicki [11] results for the mean and range (in brackets), are shown in Table 7.  
It should be noted that only two gauges were available for the field tests [11], one of which was kept for location A while the other was shared between the B locations. Therefore, the results given for gauge A have a richer data set, and the range given for the B gauges is not indicative of all the tests conducted and results from gauge A. Figures 13-15 show overlaid 75% and 100% overpressure time histories scaled up to 250%, overlaid with test data from [11]. Gauge A is located in close proximity to the explosive and is directly in the line of sight of the detonation. As a result, it is highly influenced by the charge setup conditions. There could be several reasons explaining the variability observed at gauge A. One proposed reason was the effect of the detonator on the aspect ratio of the charge mass and, consequently, the behaviour of the reflected pressure. Further numerical work should be conducted to determine the influence of detonators on different-sized charge masses. The size of the detonator in relation to the charge masses used in the laboratory tests would likely be a cause for the difference. It is assumed that a similar wired electric detonator was used in both the field and laboratory tests (21.3 g and 9 g charge masses versus a 400 g charge mass). The size of the detonator and its net explosive content remained consistent for both the 75% and 100% scale tests, meaning it could not be scaled accordingly. However, specific details regarding the detonator size and net explosive content were not provided in the field trials [11]. In the field trials [11], the presence of wind (3.4 m/s) and the use of string to hold the charge would make it difficult to ensure the detonator and charge were oriented parallel to the front wall. Oscillations were observed in the field trials. Slight changes to the orientation angle can cause significant differences in the overpressure and impulse  
Figure 13: Overpressure–time histories and cumulative specific impulse at gauges A and B1 for the 250% (black) with predicted 75% (**a**) and 100% (**b**) laboratory-scaled tests. generated, as observed in [PERSON] et al. [39] for cylindrical charges with an aspect ratio (length/diameter) of 2. It is also noted that the pressure mounts in the field trials were very slender, so the wind may have affected the positioning of the pencil pressure gauges (whereas the pressure gauges herein were mounted onto steel pipes fixed to the base via screw mounts). Furthermore, the difference in detonator position (middle-centre detonated in the lab-scale work and rear-below centre detonated in [11]) may also affect the initial peak pressure at gauge A. [PERSON] et al. [39] showed that the peak pressure was approximately 8% lower for the middle-centre detonated cylindrical charge (L/D = 2) compared to a rear-centre detonated cylindrical charge at \(Z=1.83\) m/kg\({}^{1/3}\) (the location of gauge A). This did not account for the effects of reflection from the front wall, as the work in [39] was a free field with the charge situated on the ground. Hence, the true pressure and impulse states would be more complex given the lower detonation position in the field trials. In addition, two different explosive materials were used (TNT for field experiments and PE-4 for laboratory experiments).