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ON THE STABILITY OF STRUCTURALLY HETEROGENEOUS ROCK MASS
Abstract
In this work in terms of the ideas of the zone of inelastic deformations generated around stress concentrators in heterogeneous rock mass as a quasi-plastic block medium having a microstructure, rigorous criteria of rock mass stability are obtained that naturally take into account mining-geological and geomechanical conditions. Theoretical ideas added to the problems of underground structure stability permitted to provide an explanation for paradoxical, in the view of classical representations, numerous cases of mine working collapse within relatively hard surrounding rocks, relatively soft rocks being stable. Numerical analysis of the stability criterion obtained for different types of rocks, taking into account their actual physical and mechanical characteristics, has allowed determining that in a wide range of strengths collapse occurred at approximately equal stress level. All mining methods involve creation of cavities that differ in shapes and dimensions, which contribute to the natural stress state failure and formation of the areas of increased and decreased stresses. Result of these is development of deformation processes of different velocities and rates. Separate rock mass areas being solid and coherent become a loose or discontinuous block medium. Rock subsidence movement takes place and troughs, landslides and holes form on the surface. Analysis of experimental data shows that rock instability is accompanied by creation of marginal state zones where elastic and plastic properties of bodies become apparent, which are destroyed later on in conditions of non-uniform body stress states. Thus, it is the behavior of inelastic deformation zone depending on the general rock mass stress state change, characteristics of support to be placed and also on the history of its loading that determines stability of the whole of “support-rock mass” system on the whole. The key issues in respect to geomechanics are elaboration of criteria that determine stability of elasto-plastic system as a whole.
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References16
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