Seismoacoustic evaluation of the effect of blasting on rocks

Abstract

1. Blasts change the properties of rocks considerably, the degree of this change depending considerably on their initial properties in the presence of equal dynamic stresses from the blasts. 2. In relatively strong rocks (V0=3750 m/sec, Edef≈100×103 kg/cm2) the detonation of a 14-kg charge changes their properties in a zone with a radius of 13 m. An intense effect of the blast (change of V up to 50%) is felt at a distance of 5–7 m. 3. In weak rocks (V0=1800 m/sec, Edef≈20×103 kg/cm2) the effect of the blasts is felt at a greater distance (15–16 m) even in the presence of a preliminary cleavage slit. 4. At the site of the Inguri dam the preliminary cleavage slit reduced about twofold the intensity of the destructive action of blasts on the initial elastic and strength properties of the rocks, being a unique shield for elastic vibrations. 5. The results of the investigations showed the effectiveness of using engineering seismoacoustic methods for evaluating the character of the blast effect of unit charges on rocks. Obviously it is necessary to continue investigations in this direction for determining the zone of influence of unit and group (massive) blasts on the properties of rock slopes with perfection of the experimental method. 6. On the basis of the experimental results presented, the following recommendations are made for conducting drilling and blasting operations in hydraulic construction: a) in selecting the parameters of drilling and blasting operations in rocks it is necessary to proceed from the magnitude of the initial rock characteristic obtained from the results of seismoacoustic investigations; b) for selecting safe distances to the surface being preserved it is necessary to determine the zone of influence of the blasts on the basis of experimental works in rocks of each strength zone of the mass being excavated.