1. State Key Laboratory of Coal Mine Disaster Dynamics and Control,Chongqing University,Chongqing　 400044,China; 2. College of Resource and Environ- mental Sciences,Chongqing University,Chongqing　 400044,China; 3. School of Safety Engineering,North China Institute of Science and Technology,Lang- fang　 101601,China

为研究材料失稳型冲击地压失稳的发生判据,开展了摄像实时观测情况下,煤体受端部位移约束的冲击倾向性煤体压缩破坏实验。首先,探索了实验室尺度下冲击煤体的破裂特征,然后采用有限元数值分析的方法对比分析了工程尺度下煤体发生冲击地压前的破裂趋势。最终基于实验和数值分析结果,建立了塑性应变梯度理论下的材料失稳型冲击地压的触发判据。冲击煤体压缩破坏实验结果表明:端部约束煤体发生破坏时,煤体呈现冲击破坏的特点,并分阶段发展,每个阶段都伴随着不同程度的声音信号与相关的特征信息。当应力达到强度的60%时,有少量煤体喷射;达到78%以上时,较多的煤体发生冲击,具有明显的喷射特点;接近峰值强度时,有大量煤体臌出,但无喷射特点。煤体破裂形式整体上表现为拉剪混合破裂,形成的破裂面呈内凹三角形状,与冲击地压现场煤体破裂面类似,表明实验结果具有一定的参考意义。不同高径比的煤体破坏的峰值强度略有不同,小高径比煤样的抗压强度稍大、破裂面内凹深度减小。采用有限元数值分析方法显示,巷道侧壁围岩容易在巷道变形过程中形成内凹三角形状的塑性变形集中带,从而在冲击地压发生中形成三角状的破裂面。基于内凹破裂面形态和塑性应变梯度理论,采用应变软化本构,从静力平衡和能量平衡角度,建立了煤体发生破坏前材料冲击失稳的判定准则。

To investigate the material instability to the rock burst phenomenon,a series of uniaxial compression tests on outburst-prone coal specimens under end-strain-restriction were conducted along with a real-time video recording. Firstly,the failure characteristics were analyzed in the laboratory,and the obtained results were compared with the nu-merical simulations of the coal’s rupture potential. A rock burst criterion was developed based on the analysis of the samples’ rupture surface as well as the double linear constitutive relationship. The experimental results showed that the rupture mechanism of coal specimens during the experimental tests displayed a stage-by-stage development provi-ding some predictive information such as internal sounds. When the stress inside the coal reached 60% of its(uniaxial compression) strength,a small amount of coal started to be ejected. At 78% of its total strength,a significant portion of the coal specimen blew up and when the internal stress reached a value close to the total strength, the coal were pushed out gradually,without ejection. The rupture mechanism of coal in these end-strain-restriction experiments could be defined as tensile-shear mixing modus,displaying a scooped-triangle shaped surface. These characteristics formed gradually and predictively throughout the process,implying that the experimental results have a satisfying level of sig-nificance. It has also been found that the decrement in the height-to-diameter ratio could enhance the coupling stress and reduce the coal fracture surface. Using the finite element method,it can be observed that the rock around the side-wall is prone to form the scooped-triangle local deformation bands that evolve into a rupture surface during rock bursts. Based on the morphology of the rupture surface and the theory of strain-gradient plasticity,an instability criterion was established on the point of static balance and energy balance,using a constitutive model of strain softening.

FAN Jinyang,JIANG Deyi,OUYANG Zhenhua, et al. Material-instability rock burst criteria based on the theory of strain gradient plasticity[J]. Journal of China Coal Society,2018,43(11):2959 -2966.