Dissipative structure feature of mining fractured overburden system and threshold effect of catastrophic instability

The fracture overburden was considered as a system, and the dissipative structure characteristics during the dynamic evolution of mining overburden fracture system have been analyzed. Fractal dimension of mining fractures in the overburden has been used to describe the evolution of the fracture, fluctuation and transition of the system. The "pore pressure entropy"has then been introduced to study the entropy change in dissipative structures of mining fractured overburden system. Based on the asymptotic-equilibrium generalized force and generalized flow, the super-generalized force and the generalized flow driven by it whichis far from the equilibrium non-linear region, have been defined. The dynamic instability threshold with mining scale as the index has been analyzed according to the super-entropy critical criterion. The results have shown that the relationship between fracturing degree of overburden and goaf space can be escribed by dissipative structure theory, and the possible range of "huge fluctuation" can be predicted. In addition, Pore pressure entropy can be used for describing the "entropy reduction"in the evolution from natural state to mining state in mining overburden fracture system. The quadratic variation of pore pressure entropy, taking slope of the curve of mining scalegeneration as system, can be generated with super-entropy which is far from equilibrium state in the non-linear zone, and it is used as an index to determine the three system evolution trends under external constraints. And the threshold effect of system instability of the waterproof performance is revealed at critical mining scale. © 2019, Editorial Board of Journal of Mining & Safety Engineering. All right reserved.