Composition and microscopic structure of coal in relation to unloading ejection:a correlation analysis
During the comparative evaluation,we selected coal seams(easy ejection coal samples,re-ferred to as T-e)from Ordos coalfield in Inner Mongolia Autonomous Region,and coal seams(difficult ejection coal samples,referred to as T-d)from Heze coalfield in Shandong Province.Based on the in-herent properties of coal,true triaxial compression tests under high-stress unloading condition were car-ried out.The strength characteristics and the failure process were analyzed,and the difference correlation between microscopic fracture characteristics at the rupture face and the ejection degree were also dis-cussed.The results indicated that T-d had a low content of oxygen(O)and a high content of aluminum(Al).There was a significant enhancement of the refined grain,fracture and tensile strength,and no-ticeable impact toughness.The composition factors that affected the ejection difference were O and Al.In T-e,there were obvious microstructures such as cracks and bedding structures.These microstructures were characterized by extensive development and a strong skeleton pattern,and they were structural in-ducements that affected the ejection difference.Different mechanical behaviors were incurred due to the differences of inherent properties of coal,such as low T-e peak strength,low elastic modulus and large strain rate.Under the combined influence of tensile and shear stress,the sample displayed compound failure characteristics involving macro-micro failure,noticeable ejection,extensive and intense fracture.The acoustic emission(AE)events and accumulated energy of the T-e(tension-shear)increased sharp-ly,exhibiting a three-stage pattern.Notably,the unstable fluctuation stage witnessed a high energy re-lease.This research offers insights into the correlation between internal factors of coal and unloading e-jection failure.Additionally,it presents a novel experimental demonstration for evaluating the impact tendency of a coal seam and establishes a foundation for targeted prevention and control of ejection.
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维普
