## 4 Conclusions  
The conducted tests lead to the follows conclusions:  
* The obtained stress-strain characteristics of the sandstones in the static range (UCS and BTS tests) indicate that Barwald and Apricot Pink sandstones behaved comparably, which is reflected in their similar values of longitudinal elasticity modulus and strain energy. On the other hand, Kandla Grey sandstone was characterized by significantly lower deformability and an approximately twice-higher compressive strength. This is due to its significant homogeneity resulting from the low pore content and small grain size of the material. * As regards static tests, there was no significant impact of the porosity of the tested sandstones on their strength and deformability parameters determined in the static tests. The calculated strain energy (W\({}_{\text{s}}\)) values for individual sandstone samples are proportional to their strength parameters. In other words, in the static range, the higher the rock compressive strength (UCS), the higher the W\({}_{\text{s}}\) value. * As opposed to static tests, the porosity of the samples in dynamic tests has a significant impact on the energy parameters of their cohesion destruction process. As part of the research, the amount of energy absorbed by rock samples in dynamic tests (W\({}_{\text{d}}\)) was calculated. The research indicates that the values of this parameter for Apricot Pink and Kandla Grey sandstones (slederness L/D = 34 and L/D = 42) are similar, although uniaxial compressive strength (UCS) of Kandla Grey sandstone is approximately 60% higher than that of Apricot Pink sandstone. The nature of the influence of porosity on dynamic stresses in rock it comes down to the fact that a material with more voids is more easily compacted, so there are greater differences in DIF and greater maximum strains at lower stresses. The above is the result of material cracking. * The results of dynamic tests carried out by the SHPB method indicate a significant impact on the strain rate and an increase in dynamic stresses in sandstone samples. In the case of Apricot Pink sandstone, DIF = 2.85 was obtained for the average strain rate \(\dot{\epsilon}\) = 136.16 1/s. The maximum DIF value for Kandla Grey reached 2.7 at the average strain rate \(\dot{\epsilon}\) = 53.4 1/s, whereas in the case of Barwald sandstone, the DIF value of 4.54 was obtained at the average strain rate \(\dot{\epsilon}\) = 108.34 1/s. * As a result of the conducted research, it was found that the fineness of rock samples corresponded to the amount of energy absorbed by individual samples. In the case of Apricot Pink sandstone, a relatively large dust fraction was obtained (<0.5 mm). Due to the reduced porosity of the other two materials, the samples were less pulverized. The observed phenomenon is generally consistent with the Rittinger or Kick hypothesis, which assume that energy expenditure for the crushing process grows with an increase in the fineness of the excavated material. * The development of dynamic stresses is influenced not only by the value of porosity but also by the distribution of voids in the sample. Tomographic images of Apricot Pink sandstone revealed some concentrations of pores, while in the case of the other two samples, the distribution of pores can be assumed to be uniform. The above characteristic could have reduced the ability of the Apricot Pink sandstone samples to dissipate impact energy, which translated into reduced dynamic parameters (Peak stress, W\({}_{\text{d}}\)) in relation to the other two materials subjected to analysis (Barwald, Kandla Grey). * The issue of the impact of rock structure (porosity) on dynamic loads has great development potential, especially with the use of computer simulation by the DEM method. The use of simulation will significantly expand knowledge about dynamic phenomena in the context of porosity changes.