The study of industrial explosions is made difficult by the high pressure and temperatures arising from the detonation of large charges, and by side factors which are difficult to allow for. Simulation by models enables us to cut down the number of costly industrial experiments while maintaining identical conditions so that laboratory resuits can be applied to the full-scale prototypes. The breakup of a medium is governed by its physical and mechanical properties, the characteristics of the explosion, and the conditions of blasting. These factors must be taken into account when designing a model of the process.Breakup is a complex nonstationary process, which can arbitrarily be divided into three main stages: propagation of the stress field, fracture formation, and separation of the fragments formed. In previous work on models of breakup by blasting, the similitude criteria do not allow for the fracture-formation stage, which is critical for the fragmentation process, or the time characteristics of the breakup process. The aim of our present work is to establish similitude criteria which will take account of one phase of the breakup process, namely, fracture formation.The theoretical analysis of the breakup process is based on the hypothesis of A. A. Griffiths and M. V. Machinskii, who postulate that in any body there are defects (microfractures) from which macrofractures originate when a stress field passes. In the propagation of the stress field due to the explosion of a charge, in some volume dv of the medium, dn fractures will open up. The density of sites of origination of individual fractures n o is governed by the maximum applied stress and by the strength properties of the real and model materials, no= ,(s) ds, Ser O)where S is the surface area of a crack, ~(S) is the differential distribution function of the dimensions of the cracks, o is the applied stress, and Scr(O) is the surface area of the smallest crack opened by the stress.As the stress wave spreads, the maximum stresses in it will decrease owing to geometrical expansion and dissipative energy losses in real media: The density of crack initiation sites will be some complicated function of the distance from the charge center, ,r%= (r)]where n o is the number of initiation centers in unit volume, o 0max is the maximum stress at the wail of the blast hole (charge cavity), lob] is the breaking stress under static load, r0 is the radius of the charge, and r is the distance from the charge center.If the body is cylindrical, the total number of crack initiation sites will be R It~ (r)]rc, r n : 2~H, f[-[-~cO 7~o0 where H is the length of the body and R its radius.

TOLOADS UDC 622.235Rock bursts occur when blasting is carried out in deep horizons of Donbass collieries in sandstones with a Protod'yakonov hardness f= 6-10. It is assumed that this is largely due to the stressed state of the rock mass induced by the pressure of the overlying rocks, tectonic processes, and saturation of the rock with gas at a pressure of 30-100 atm.Before a working is driven, the rock mass is in a state of volumetric stress. When the working is driven by blasting, the explosions cause additional stresses in the rock mass, which reach 35-280 kg/cm z, depending on the properties of the rocks and the properties of the explosives at the contact of the charge with the rock. At a distance of up to 15 charge radii from the explosion center, the shock waves are propagated at ultrasonic speeds; at a distance of 15-500 radii, the stress waves are propagated at the speed of sound, the stresses retaining fairly high values.Under the conditions of hydrostatic load, at a distance of 10-20 charge radii from the explosion center we observe plastic deformations -a zone of overcrushing of the rock at concentric circumferences. There are no radial fissures in the walls of the cavity. During the explosion, at a distance of 20-400 charge radii a wave of reversible deformation of the rock is formed. It is due to the potential energy of an elastically compressed medium; hence its effect is manifested after part of the rock mass has been detached. The reversible deformation wave is a tension wave and is displaced only toward the free surface. On these grounds we may infer that the stresses induced by firing shothole charges are an additional pulse which leads to the ejection of rock.Methods which control the stress field parameters enable one to reduce the probability of occurrence of bursts. The value of the stresses being propagated into the heart of the rock mass depends on the pressure at the shock front. The pressure at the shock front may be greatly reduced by using linings of materials with an acoustic impedance markedly different from that of the rock being blasted, the: ~. linings being located between the charge and the wall of the blast hole. The pressure (stress) transmitted to the rock mass in absence of a gap is determined by the equation oma x = k Pay N/m2'where k is the refractive index 2 p, C,where Pl is the density of the medium, in kg/m s, C, is the velocity of the longitudinal wave, in m/sec, Pex is the density of the explosive charge, in kg/m s, and Dex is the detonation velocity of the explosives, in m/see.As the shock wave passes through the lining, the stress is reduced by refraction of the wave at the chargelining and lining-rock interfaces.The stress transmitted to the rock mass through the lining in the forward elastic wave is calculated by the equationInstitute of Geotechnical Mechanics, Academy of Sciences of the URrSSR, Dnepropetrovsk.

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When rocks are extracted in building-stone and limestone quarries, in addition to the maintenance of highgrade crushing during blasting, one must reduce the yield of overcrushed rock, which depends on the pressure pulse parameters in the charge chamber, characterized by the rate of increase and value of the maximum pressure, and on the duration of the pressure above this level. We will establish the effects of each of these parameters on the stress field characteristic and the crushing intensity of the rocks.The effect of the rate of pressure increase in the shock wave front on the parameters of the stress field created by an explosion in a medium can be established in an elastic approximation. Such an assumption is perfectly acceptable because the fracture time is much greater than the duration of pressure increase in the charge chamber when commercial high explosives are used. Let us assume that the charge cavity of radius r 0 is located in an ideally elastic infinite area. (The condition of limitlessness is automatically satisfied for all laboratory and industrial explosions, because during the period of pressure increase in the charge chamber the stress wave does not reach the free surface.)The one-dimensional stress wave created by the explosion is represented by a single system of generalized equations:Oa r

loss of AN from the charge in two months did not exceed 5%. Tests on the above compositions charged under a separating layer revealed that in this case the AN loss is reduced to a minimum. CONCLUSIONS 1. Of the thickening agents used at present to gelatinize water-filled aluminized compositions, apart from starch and cereal flour, the best results from the viewpoint of charge stabilization in water-laden boreholes are obtained by adding polyacrylamide (PAA). The use of chrome potassium alum (CPA) or chromium sulfate as cross-linking agent in combination with PAA improves the stability of the charge and increase its water resistance.2. Addition of the sodium salt of carboxymethylcellulose (CMC) as thickening agent in aluminized WFE causes copious gas emission and swelling and layer separation of the charge, and in some cases even separation of water and formation of hydrargillite. Addition of borax solution as a cross-linking agent in combination with CMC has little effect in reducing the gas emission and layer separation of WFE with aluminum. These factors show that it is undesirable to use CMC in water-filled aluminum-containing compositions.3. Experiments show that as an individual thickening agent for aluminized WFE, not requiring a crosslinking agent, successful use can be made of starch or cereal flour, added by means of a technology developed at LGI. The water resistance and stability of the WFE with aluminum are better than the analogous indices of compositions based on traditional thickening agents such as PAA or GG. 4. By charging under a separating layer, whatever the stagnant water column height it is possible to reduce the AN losses from the charge to a minimum. THE ROLE OF GASEOUS DETONATION PRODUCTS IN EXPLOSIONS IN GRANULAR MEDIA V. V. Vorob'ev, I. G. Zakharova, V. M. Komir, V. M. Kuznetsov, and A. F. ShatsukevichThe extensive use of blasting has imposed stricter requirements on the efficiency of industrial explosions. Bearing in mind that in explosions in the ground the efficiency is no more than 4-6%, we can readily understand the interest displayed in the physics of an explosion in the ground, the calculation and selection of efficient blasting parameters, the selection of the optimal range of explosives (E), and the rationalization of operations associated with explosive charges.Recently, many reports [1][2][3][4][5] have been devoted to elucidation of the relative role of the compression wave and the detonation products (DP) in explosions in porous media. Zel'manov et al. [ 1] gave the results of experimental investigations of an electrical explosion in dry sand. Since such an explosion has practically no true explosion products, to estimate the influence of DP on explosive loading of granular media, gas-forming substances (iodine crystals and ammonium chloride) were added to the center of the electrical explosion. Measurements showed that with addition of gas-forming substances the mass velocity increases by a factor of 1.3-2. The introduction of gas-forming substances increases the efficien...