Self-organizing dynamic instability mechanism of rocks with high rockburst proneness
In order to explore the dynamic instability mechanism of rocks,uniaxial acoustic emission tests on rocks with high rockburst proneness were carried out.The stress-strain,acoustic emission evolution,macro and meso failure characteristics were analyzed.The results indicate that the dynamic instability of rocks is a self-organizing behavior of their meso-structural systems gradually forming a certain shape of mechanical structure,and then the mechanical structure suddenly collapses,which has the properties of self-organized criticality,symmetry breaking and loss of plasticity.The dynamic instability process of rocks was divided into two stages:energy accumulation and energy explosion.Based on the self-catalysis self-inhibition mechanism of self-organizing systems,the nonlinear dynamic equations for energy accumulation and energy explosion considering symmetry breaking were established respectively,and the corresponding dissipative energy evolution equations were derived.The binary medium theory was introduced and the breakage of rocks was regarded as the transformation of elastic-brittle cementation elements to elastic-plastic friction elements.The friction elements follow the Mohr-Coulomb criterion.The breakage law was defined according to the dissipative energy evolution equation of the energy accumulation stage.A binary medium model for rocks was established.The damage law was defined according to the dissipative energy evolution equation of the energy explosion stage and a damage model for rocks was established.The mechanical models were embedded in the finite difference software and were verified as correct.Based on the self-organization theory and combined with the numerical simulation results,the dynamic instability mechanism of rocks was analyzed from the perspective of energy and meso-scopic level.The results show that the meso-structural systems of ideal homogeneous rocks can evolve intoa centrally symmetric mechanical structure in the shape of hourglass under the influence of potential energy gradients.At the critical state,the potential energy gradient surfaces are densely gathered toward the center of the mechanical structure and the energy can flow at high speed within the surface.The rock bridge located at the symmetrical center can be easily torn apart,which can break the potential energy gradient surfaces around it and trigger a intense release of the in-plane energy and rock burst.The mechanical structure and failure mode with symmetry breaking will occur during the instability process of real rocks.The research results can provide theoretical support and numerical simulation means for the dynamic instability analysis of rock pillars and tunnel surrounding rock.
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