Changes in rock and rock mass properties in the close-in zone of large-scale underground explosion

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. ne 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/kt(1/3). 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.