ABSTRACT
The materials of which rock masses are made possess certain physical characteristics that are a function of their origin and of the posterior geological processes which have affected them. The densities and strengths of rocks are normally quite well correlated. In general, low density rocks are deformed and broken quite easily, requiring relatively low energy factors, whereas dense rocks need a higher quantity of energy to achieve a satisfactory fragmentation, as well as a good displacement and swelling. All rocks in nature have some type of discontinuity, microfissures and macrofissures, which decisively influence the physical and mechanical properties of the rocks and, consequently, the blasting results. In tunnel excavations, the structural characteristics largely condition the geometry of their profile, almost rectangular if the rocks are massive and with a curved arch if the rock is more unstable. When the discontinuities are normal to the tunnel’s axis, the blasts usually have good results.
