## 3 Dynamic Tests with the Use of Hopkinson Split Pressure Bar (SHPB)
The grain size distribution of individual sandstone samples is shown in Figures 14-16, whereas the quantitative results of the grain analysis are presented in Figure 17. The performed grain analysis indicates a significant increase in the smallest fraction (<0.5 mm) in the case of the sandstone with the highest porosity (Apricot Pink). The reduced porosity of the samples was generally associated with a decrease in the fineness of the excavated material. In the case of Kandla Grey sandstone, an increase in relation to Barwald sandstone is particularly visible in the fraction of 5-2 mm and 2-1 mm, with a simultaneous decrease in the fraction < 0.5 mm. The evaluation of the measurement uncertainty of the data presented in Figure 17 was based on Student's two-tailed \(t\) test. Figure 14: Gradation test for Apricot Pink sandstone (average value \(\dot{\epsilon}\) = 136.16 1/s): (**1**) >10 mm, (**2**) 10 \(\div\) 5 mm, (**3**) 5 \(\div\) 2 mm, (**4**) 2 \(\div\) 1 mm, (**5**) 1\(\div\) 0.5 mm, (**6**) <0.5 mm. Figure 13: Stress–strain response of Kandla Grey sandstone (L/D = 1). Figure 18 presents the average values of the maximum dynamic stresses recorded during the tests. Generally dynamic stresses increase in different proportions to static stresses, depending on the type of sandstone. An increase in the strain rate causes an increase in dynamic stresses. A change in sample slenderness significantly increases dynamic stresses, especially in the case of Apricot Pink and Kandla Grey sandstones. The influence of strain rate on the increase in dynamic stresses is slightly smaller in the case of  
Figure 17: Gradation test results. Barwald sandstone. A comparison of the DIF coefficient of the tested materials indicates a similar trend. The DIF value for Apricot Pink and Kandla Grey sandstones ranged from 1.15 to 2.85, depending on the slenderness of the sample, whereas in the case of Barwald sandstone, the DIF coefficient turned out to be much higher--from 2.64 to 3.54, depending on sample slenderness. This is illustrated in Figure 19. Important information about the materials' behavior is provided by the amount of energy absorbed by the samples. The values of energy absorbed by sandstone samples are presented in Figure 20. The obtained results demonstrate that the amount of energy dissipated by Apricot Pink and Kandla Grey sandstone samples with slenderness L/D = 3/4 and L/D = 1/2 are similar despite the fact that these materials differ significantly in their uniaxial compressive strength (UCS). The evaluation of the measurement uncertainty of the data presented in Figures 18-20 was based on Student's two-tailed \(t\) test. The test results show a significant impact of porosity on the energy parameters of the process of destructing rock samples under high strain rates. This is important in the context of estimating the energy consumption of rock destruction processes under dynamic loads. Until now, analytical or simulation modeling of technological processes (e.g., mining, crushing) has been generally ignoring the aspect of rock structure. Expanding the scope of research in this area, especially on numerical analyses, will enable the development of adequate models describing the behavior of rocks under dynamic loads, which will translate into a wide range of applications in many areas of engineering.