Origin of the vibrations induced by tunnels' excavation

In rock excavation (especially with explosives, but also in mechanical excava-tion), the vibrations of the medium where the excavation develops (rock mass) and those of the surrounding air (sound) are of great importance. After a synthetic description of the most common expressions of the "site laws" (charge-distance-vibration intensity correlations), attention is paid to the different types of technical problems where such correlations can be employed, on the basis of experimental cases and of literature data. Examples are presented consisting of suitable modifications of the excavation procedure to reduce the problem of vibrations. These modifications may concern, even jointly, the reduction of the pull, the increase of the drilling density (with corresponding reduction of the charges of the single holes), the increase of the delay numbers, the modification of the excavation system or, also, the isolation of the volume to be excavated with mechanical pre-cuts. The conclusions provide a straightforward approach to the assessment of charge per delay limits and recommendations are provided.