ABSTRACT
A new theoretical explanation is given to the phenomenon of particle velocity amplification, which manifests itself in a significant (4–10 fold) increase near and at the surface of an excavation compared to the particle velocity of a wave inside solid rock. A mechanism of energy release is proposed which emphasizes the role of softening at interacting surfaces of cracks or/and blocks. As softening occurs in a limit state, the effect appears only under sufficiently high stresses. In particular, the effect can be expected, and appears in fact, at cracks near openings in hard rock in deep mines.
