ANALYSIS OF THE RESULTS OF INVESTIGATIONS AIMED AT REDUCING THE ROCK STRENGTH IN SERIAL EXPLOSIONS OF BOREHOLE EXPLOSIVE CHARGES
This article discusses issues involved with changes in the strength properties of rock mass during serial explosions of borehole explosive charges while performing mining operations in quarries. During the analysis of the research methods for changing the strength properties of rock mass, the zones of decrease in rock mass strength beyond the quarry contour, which are formed as a result of multicyclic explosive loads, were not taken into account while determining the parameters of borehole charges in a row.In a quasistatic simulation of a single explosion leading to rock destruction, the nature of the propagation of radial cracks in the rock resulting from the pressure of the shock wave, detonation products, and stress concentration in the vicinity of the crack tips was revealed. Moreover, the growth of cracks in granite due the explosion occurs within 15 ms, and in limestone within 20-25 ms, depending on the physicomechanical properties of rocks, their degree of fracturing, and the use of a special type of tamping. The operating principle of the locking tamping is based on the reflection of shock waves from the internal funnel-shaped profile, as a result of which a partial detonation of the detonation products occurs. Tamping retention in the borehole is maintained due to its expansion by detonation products.From the analysed studies conducted in laboratory conditions, the strength of ore limestone and magnetite samples after a single explosive loading was found to decrease by 38.6 and 40.8% of the initial static compressive strength, respectively, and after repeated exposure, on average, 5-10%. The dimensions of the zone of reduced strength in the surrounding massif was found to be dependent on the height of the quarry ledge and the energy characteristics of applied explosives.