Nature and mechanism of rock and gas outbursts

Abstract

Experience of construction and operation of deep mines proves the necessity of making deep-level openings in the strongest rocks, mainly, in sandstone, limestone and dolomite. However, such rocks at a depth of 800 m and deeper are the most rockburst-hazardous. Rock outbursts impair safety of mining, and lead to deceleration and appreciation of production processes. The study into the failure-causing residual stresses in rockburst-hazardous rocks is performed. The direct tests of the residual stresses in rockburst-hazardous sandstone make it possible to state the absence of such stresses and, thus, the absence of the residual tectonic stresses in such rocks. The petrographic research proves the essential and crucial role of diagenesis when physicochemical transformations of rocks are assessed. These transformations reinforce the conclusion on the absence of the residual tectonic stresses in rockburst-hazardous sandstone in Donbass. The main cause of the anomalous stress zones is the high-pressure gas (methane) in rocks. The internal stresses to add the gravitational stresses are governed by the swelling property of sandstone when saturated with methane and by the degree of “constraint” of this swelling. The main cause of failure in a high-stress rock mass is the transition of a brittle material from the volumetric compression to the complex stress state when there are the conditions for the elastic recovery deformation, i.e. tensile deformation. Failure is possible when the latter reaches the ultimate values. The cause of the stress redistribution is the instantaneous separation of a part of the high-stress rock mass during blasting.