Quantitative determination of mining-induced discontinuous stress drop in coal

 Xue Dongjie●Wang Jianqiang●Zhao Yongwei●Zhou Hongwei

Abstract

Mining induced stress, especially discontinuous redistribution and stress drop, is a major issue of structural stability in deep coal mining. Only considering the yield criterion as the continuous stress equation solution without failure criterion leads to excessive plastic zone and support ability. The discontinuous distribution is illustrated by abutment pressure rather than horizontal stress. First, the weakening of the stress boundary by substituting the Mohr-Coulomb yield equation into the differential equations of stress is discussed. We propose an elastic solution and discontinuous stress boundary for the stress state of coal ahead of working face. Second, it is pointed out that introducing the statistical yield criterion to the stress equilibrium equation can be used for determination of the broken zone. The failure criterion is proposed at the elastoplastic boundary considering the behavior transition for avoiding excessive stress concentration. The equation of stress drop at the transition boundary is proposed for the discontinuous solutions. The influence of the internal friction angle and cohesion on the discontinuous distribution of abutment pressure as well as the peak stress coefficient is discussed. The results show that the discontinuous equations of mining-induced stress distribution effectively represent the stress state in the broken zone. The equitant damage is defined in the broken zone based on the deterioration of rock due to crack generation. The stress drop at the elastoplastic boundary is compared quantitatively by MohrCoulomb’s solution and the statistical solution equation. When the uniaxial compressive strength is below the original in situ stress, the peak stress concentration is mainly a function of the internal friction angle. As the damage increases, the peak stress in the broken zone decreases and the stress drop increases. The experimental results from excavation induced testing by loading multi-stage confining pressures are consistent with theoretical solutions. Finally, the mining-induced unloading ratio is proposed to learn the excavation speed or disturbance intensity. There is a positive linear correlation between the unloading rates and the peak coefficients, and the mining-induced behavior depends on the discontinuous unloading path and rates.

引用格式：

Xue DJ, Wang JQ, Zhao YW, Zhou HW.Quantitative determination of mining-induced discontinuous stress drop in coal[J]. International Journal of Rock Mechanics and Mining Sciences, 2018, 111: 1-11

SCI:WOS-000447173800001   DOI:10.1016/j.ijrmms.2018.08.003

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