Impact of blast zone on mining processes in fractured rock mass

Abstract

Generalization of the abundant experimental and theoretical research accomplished by Russian and foreign scientists in the 20th–21st centuries enables distinguishing between a few action zones of blasting, namely, crushing zone (fine grain crushing), radiating cracking zone, induced-fracture zone, shaking zone (residual stress after blasting), and blast-induced load zone. In the crushing zone, overgrinding takes place, which has an adverse influence on efficiency of processing of uranium, for instance, or granular quartz. The radiating cracking zone size in blasting in fractured rock masses governs the quality of drilling and blasting. The induced-fracture zone determines stability of rock mass and, consequently, safety of production processes both in surface and underground mines. In the shattering zone, fractured rock mass experiences residual stresses, which induces new fractures and rock falls, or dynamic events due to lithostatic pressure in rockburst-hazardous rock mass. This article aims at the experimental and theoretical determination of geometrics of blast-induced impact zones in different geological and geotechnical conditions with a view to developing appropriate actions toward abatement of the adverse effect exerted by these zones on geomechanical and technological processes in the course of mining. The theoretical formulas are given for the radii of the crushing, radiating cracking, induced fracturing and residual stress zones. Reliable applicability of the formulas in actual mining is proved by comparison of the calculations with the full-scale testing data. To mitigate the crushing zone impact, it is possible to charge the wellhead interval with a radial air gap, which decreases density of charging. Arrangements toward reduction of the zones of induced-fractures and residual stresses are proposed. Energy of the man-mane zone of residual stresses after blasting can be targeted at activation of raise driving with raise borer 2KV.