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| Experimental and numerical simulation research on intermittent failure of structural coal#br# |
| LU Zhiguo1，2，3，JU Wenjun1，2，GAO Fuqiang1，2，3，ZHANG Quntao1，2，YI Kang1，4，#br# SUN Zhuoyue1，2，YUAN Guiyang1，2，3，DONG Shuangyong1，2#br# |
(1. Coal Mining and Designing Branch，China Coal Research Institute，Beijing 100013，China；2. Coal Mining Research Institute Co.，Ltd. of CCTEG，Beijing 100013，China；3. State Key Laboratory of Coal Mining and Clean Utilization，Beijing 100013，China；4. School of Resource and Safety Engineering，China University of Mining and Technology(Beijing)，Beijing 100083，China)
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Abstract Discontinuous structural weak planes are widely distributed in coal and rock，which causes that stress-strain curves under uniaxial compression show multiple stress drops. In order to explore the intrinsic mechanisms of intermittent failure of coal with discontinuous weak planes under loading，uniaxial loading tests were carried out on coal samples with dense fractures obtained from Tashan coal mine，Datong，and acoustic emission(AE) signals of coal samples were monitored in real time. The intermittent failure behaviors of coal samples were analyzed from the points of energy evolution，acoustic emission characteristics and failure morphology，and verified by a developed numerical model of particle flow code (PFC). The results show that the elastic deformation energy，showing a similar evolution trend to the stress-strain curve，reaches the maximum at the peak strength and releases completely after failure，and that the energy dissipation increases sharply when the stress drops suddenly and is equal to the total input energy after failure. There is a good correspondence between AE events and the stress-strain curve. When the stress rises steadily，there are fewer AE events，and most of them are low-level events. When the stress drops suddenly，a large number of high-level AE events cluster. Both AE b-value and fractal dimension D，reflecting the scale distribution and orderliness of micro-fractures，oscillate violently before approaching failure，which indicates that different scale cracks appear alternately in coal samples and adjust repeatedly from disorder to order，and there are many intermittent local failures before losing the bearing capacity completely. The numerical calculation shows that the tension crack first occurs at the tip of the primary cracks. When the stress drops suddenly，the number of bond between particles and cracks increase sharply，and the micro-cracks connect with each other to form large-scale cracks or propagate rapidly to the surface of the specimen. Local failure at different spatial locations causes zigzag of stress-strain curves at the pre-peak stage. Large-scale cracks cut specimens into independent bearing structures and destroy the bearing structure of the specimens，which is the internal cause of strength deterioration of the specimens.
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2020, Vol. 39 
