Experimental data obtained in testing nuclear devices at Semipalatinsk Test Site (USSR) were used to analyze the mechanical effects of underground nuclear explosions. The devices were detonated in tunnels and in deep boreholes. The structure and mechanical properties of the rocks and massifs were determined by special underground workings and boreholes in the cases of tunnel explosions, and by deep boreholes in the cases of shaft explosions. The spatial distribution of rock properties was determined with seismic methods. Examination of the fracturing of rock massif affected by, explosion suggests the existence of areas (zones) distinguished by different structure and mechanical characteristics. The size of the cavity, crushing zone, damage zone, zones of fracturing and block fracturing, as well as the general properties of rocks in these zones are discussed. It is shown that besides these zones, the zone of local irreversible effects characterized by local massif destruction and anomalous effects at the tectonic faults is determined. The radius of this zone is about 1000 m/kt¹/3. The results of laboratory tests of the rock samples taken at different distances from explosion are used to consider the problems connected with changes in rock mechanical properties due to underground nuclear explosion. The permeability and size distribution of the rock formed due to effect of explosion are discussed.
Investigating the mechanical properties of rocks and massifs is an important fundamental problem. Of particular interest is examining the behavior of rocks subject to considerable load. In addition to solving economic problems associated with the development of subsurface medium, mining operations, and construction, the results of such studies make it possible to reconstruct the regularities in the behavior of the Earth's inner geospheres and to describe the peculiarities of the processes taking part in natural structures of the crust (plate motion, etc.). Underground nuclear tests allowed the accumulation of valuable evidence on the behavior of rock and massifs subject to intense dynamic load. Irreversible changes in the media are among the most important effects of underground nuclear explosion. Changes in the structure and strength of rocks and massifs reduce their bearing strength, bring about surface effects in the vicinity of the explosion, and disturb the natural regimes of energy and mass exchange within a vast zone. The effect of large explosion on groundwater regime is also quite significant. Considerable recent attention has been focused on the mechanical effects of underground nuclear explosions, which were analyzed to provide data for assessment and reconsideration of the geoecological consequences of underground nuclear tests and underground nuclear explosions made for economic purposes. Destruction of a solid medium under the effect of explosive impact can be, considered, first of all,, as destruction of rock continuity and hence splitting bonds, between its separate structural elements, thus determining an hierarchical block structure of the disintegrated medium (Adushkin & Spivak, 1994, Proceedings, 1970, Stability, 1995). It is worth mentioning that in n:any cases, the individual structural elements separated by the newly-formed boundaries still remain close together. For example, camouflet nuclear explosions carried out in the absence of surfaces and zones of, relief lead to considerable deformations, caused by explosive motion, and residual stress, which make the rock massif, destroyed as it is, from a tight packing of separate rock blocks. This can be seen from experiments with releasing rocks destroyed by an underground nuclear explosion (Gustchin V.V. et al. 1975). At the same time, the destruction of rock discontinuity results in that both the rock and the massif as a whole feature distinct change in their properties (Bronnikov & Spivak, 1983, Spivak, 1997). In the present study we focus on the basic characteristics of rocks and massif in the close vicinity to the site of underground nuclear explosions detonated in drifts in the Degelen rock massif and in boreholes of Balapan rock massif in the Semipalatinsk Test Site.
