In these experimental studies the authors have chiefly investigated the characteristics of the stress waves in rocks caused by detonators or explosives. The research consisted of two parts. In the first part, we have treated mainly the phenomena which accompany the detonator's attack and have discussed the dynamic characteristics of rocks under such impulsive loadings. The following results were obtained from this part of the investigation. The values of Young's moduli for rocks obtained dynamically are about two or three times greater than those obtained statically. The dynamic strengths of rocks are also greater than the static ones, but the difference seems to be not so great as in the case of metals. Moreover, it is an interesting result that various shock effects appear in accordance with the physical properties of rocks. In the second part we advanced to a study of the phenomena accompanying an explosive's attack and observed chiefly the changes in the propagation velocities of the induced stress waves near the explosion point. The results obtained can be summarized as follows. From the results obtained concerning the changes in the velocity of propagation of the stress waves with distance, a plastic wave of higher order seems to exist in the region very near the point of explosion and the appearance of the plastic wave seems to depend not only on the physical characteristics of the rocks but also on the brisance of the explosives. The compressibility of a rock under impulsive high pressure is peculiar to the physical properties of the rock, and it has no relation to the natures of the explosive. The peak pressure of the wave front decreases very rapidly with distance, and only within a few centimeters of the point of explosion do the explosives develop a different high pressure in proportion to their brisances
