KURINNYI Vladimir & GARKUSHA Igor
Study of the processes that determine the low utilization rate of the energy of the explosion of a borehole charge, and consider ways to increase it.
Investigation of thermodynamic, gas-dynamic and wave processes occurring in the rock and in the cavity of the explosion of the borehole charge.
For the qualitative crushing and softening of the rock, it is necessary that the compressive, tensile and shear stresses, their rate of change and gradients are within the limits determined by the strength of the rock. In addition, the time of their existence should be sufficient to destroy the rock.
Modern explosives create in the rock a field whose parameters differ significantly from optimal. A very high rate of change of stresses (1015 Pa/s) and a gradient of stresses (1011 Pa/m) lead to formation of crushing and grinding zones at the well.
At a distance of several meters from the well, in the middle zone the weakening of the rock is minimal. The size of the particles, into which the rock breaks down in the zone of crushing and grinding, and hence the amount of heat released, is inversely proportional to the chemical reactions zone width in the explosives, which in modern non-granular explosives is measured in millimeters
In the case where the speed of the detonation wave is less than the velocity of the stress waves in the medium, the emulsion explosives do not detonate in the normal mode (the under-compressed mode). During the explosion, a strong compression wave overtakes the detonation wave, compressing the explosive and reducing the number of "hot-check-points
To reduce the zone of crushing, it is necessary to use charges with a shell of porous or bulk material. If there is an air gap between the walls of the well and the explosive, then with a borehole diameter of 250 mm and a gap of 20 mm, the pressure gradient decreases by approximately 4 times, and the maximum pressure of the explosion products decreases by 9%. As a shell, it is possible to apply a porous substance, which when heated, enters an exothermic reaction, for example, a thermite mixture.
As a result of the researches carried out by the authors, it was shown that the field of stresses in the middle explosion zone has a rate of change and a stress gradient that is insufficient for the weakening of the rock. In this case, the cracks grow mainly in the radial direction.
To destroy and weakening the rock under tensile or shear stresses, it is necessary to create a field satisfying the оptimal conditions. Such a field is created by combined charges and charges with inert gaps. The average mass velocity of the rock in the gap is at least half that of the rock in the explosive. The energy of the stress wave radiated by the gap is several times less than the energy emitted by the same part of the products of explosion
With an increase in the radius of the gap from rock particles compressed to a pressure of 5 GPa from r = 125 mm to r = 129 mm, the pressure in the gap would decrease to 0.1 GPa. The wave of compression in the products of explosion provides energy inflow into the gap, but the intensity of the outflow of energy is much greater, which leads to the appearance of tensile and shear stresses in the rock near the gap. For a good final processing of the sole of the ledge, air gaps near
Investigation of the wave processes occurring in the tamping of the charge allows us to conclude that, when selecting material of tamping and the blasting method, a small charge (about 10 kg) placed in the tamping allows a significant reduction in the output of the boulders from the top of the ledge
The researches were carried out within the framework of state budget researches at the Dnipro University of Technology
Keywords: explosion, zones of destruction, structure of borehole charges