The stress state of a rock mess siEnificantly affects the indices for explosive breakout of mineral resources, while the nature of the explosion results' dependence upon rock pressure is not unique. It is well known that omnidirectional compression makes destruction proceeds while carryinE out explosvie operations or impacts upon the rocks, load-relief waves caused by the redistribution of static stresses, can initiate rock busts and can evoke an increase in the bulk of the destruction. At the present time, quantitative patterns in the process of dynamic rock-pressure redistribution have been studied comparatively little, althouEh they also are of siEnificant practical interest. In particular, the results of similar studies can be used to perfect the technology for conducting explosive operations at deep shaft levels and in regions where high tectonic stresses operate.In this work, the process of change in the stress state of a rock mass is considered during the instantaneous destruction of its near-face region. The effect of dynamic loads arising durinE the redistribution of rock pressure and explosions upon possible destruction beyond the edEe of the rock mass is also considered. The results of shaft experiments are presented based on determininE the rupturability of the roof rocks in underEround excavations. STUDY OF THE PROCESS OF DYNAMIC ROCK-PRESSURE REDISTRIBUTIONThe results of studyinE the mechanism of rock-pressure redistribution durinE an explosion are contained mainly in works devoted to questions of conductin E excavations in locations danEerous due to rock burst [1][2][3][4]. It is noted [i] that in an explosion, redistribution of the stress state and deformation of the rock surroundin E the charEe occurs. With the formation of a new, open surface in the rock mass, load-relief waves are formed, which leads to the transfer of the potential enerEy of bulk compression into kinetic enerEy of movement...particles of the rock are moved toward the surface of the rock exposure. As laboratory experimetns indicate, at a specific level of potential enerEy of compression, rock burst occurs. The seismic action of the explosions also plays a substantial role in the release of rock bursts [2,3].In a rock burst, limited destruction takes place near the exposed surface, which leads to a new stress redistribution.This, in turn, makes possible a new limited destruction in the near-face zone and contributes to further development of the burst [4].In the works pointed out above, the process of static-stress redistribution is described durinE explosive break-out in mining excavations. We note that analoEous effects have been recorded in a number of underEround nuclear explosions.The presence on seismoEr-m-of anomalous transverse waves is considered to be evidence of the relaxation of tectonic stresses durin E the explosion [5][6][7]. Estimates, made on the basis of laboratory experiments, of the amount of enerEy w~ich is Eiven off durin E an explosion in a stressed medium, confirm the mechanism of the radiation of transve...

At the Dzhezkazgan deposit the increasing depth of the mine workings has led to several cases of unjustified high losses of ore left in the pillars.This has made it necessary to determine the optimum parameters of the room-and-pillar system of working.A successful and practical solution to this problem is assisted by the use of mining geophysics to make a detailed investigation of the state of stress and the elastic properties of the rocks in the pillars, and of the disturbed zones induced by shaping of the pillars by drilling and blasting.This article gives certain results obtained by the use of ultrasonic sounding to investigate the elastic properties in a circular interchamber pillar (diameter 9 m, height 7 m) composed of strong flne-gralned sandstone and located in a horizontal bed of mine No. 45 (+235 horizon).A prel~m~nary inspection of the exposed surface of this pillar showed that its rocks are broken up by a network of cracks and mlcrocracks running in all directions due to drilling and blasting.

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To ensure efficient and safe mining operations, it is important to know the stress in the rock mass around mine workings and its distribution pattern.It is known that mining operations in any rock mass disturb its internal extuilibrium, At the points in the rock mass adjoining the generatrix of the cavity the stresses are redistributed and concentrated around the working, This is the principal physical cause of the change in the properties of the rock around the working.Depending on the rock strength, two types of mechanical state of the rock mass around a working are most frequently observed; corresponding to these, two types of distribution of the acoustic characteristics of the rocks are noted as we go deeper into the rock mass and further from the periphery of the working [1].Rocks with higher stability, i.e., capable of withstanding the total stresses arising at the periphery of tim working and not in need of any support, are characterized by the elastic wave velocity distribution shown in Fig, la: