| Jurassic coal seam and Carboniferous coal seam exist in Datong mine area, which is named "Double System" coal seam for short. Carboniferous extremely thick coal seam is mined by fully mechanized caving method in Tongxin coal mine. Serious strata behavior occurred frequently in complicated mining conditions due to several pieces of hard roof in overlying strata and the left pillars of multi-seam mining in Jurassic system. Therefore, hard roof movement characteristics and the strata behavior law should be further research. The research results will provide a theoretical guidance for the safety and high effective production of extremely thick coal seam in Datong mine area.In this paper, the mechanical model of "Arch shell" overlying strata huge structure has been established during mining in panel, geometric characteristics and movement characteristics of overlying strata huge structure has been analyzed. The huge structure scale is determined by hard rock strength, thickness and mining thick and the key strata control huge structure formation and evolution. Combined key stratum theory and materials mechanics theory, energy calculation formula of huge structure first instability and cycle instability is identified, the calculation results show that strata behavior is controlled by huge structure formation and instability, reveal strata behavior characteristics of the huge structure surrounding rock stress increases during formation process, energy suddenly release when the structure instability and surrounding rock stress decreasce after structure instability.MFOA-SVM overburden failure height prediction model has been established based on improved fruit fly optimization algorithm and support vector machine theory. The height of overburden failure in extremely thick coal seam of Carboniferous is predicted by this model, predict results match EH4 physical detection results, the model is well applicable. Movement and destruction law of overburden, and the influence of mining in "Double system" coal seam has been researched by using similar material simulation method, result show that hard rock breaking control mining face strata behavior intensity. FLAC3D numerical simulation software has been used to simulate the mining process in Jurassic coal seam group and Carboniferous coal seams to determine the fracture development of "Double System" coal seams, "Double System" seams goaf fissure mutual connectted after coal mining. Distribution of microseismic events and characteristics of microseismic energy and frequency under the influence of "Double system" coal seams has been studied by using microseismic monitoring method. goaf overburden strata remain moving behind the mining face 300 m～500 m. and strata movement is more strongly when mining under the Jurassic overlap pillar area.Mining-induced stress evolution law of Carboniferous panel under the influence of Jurassic coal pillar has been researched by using UDEC numerical simulation software, surrounding rock stress increases when mining face under Jurassic coal pillar area, the stress increase by 32%～ 37%. The temporal and spatial evolution law of strata behaviors has been certained based on the monitor work of road way and mining face, further validate that strata behavior is controlled by the huge structure. The strata behavior of different moving speed of the panel in extremely thick coal seam has been researched by surrounding rock stress, support working resistance and strata movement characteristic. The faster mining face moves, the more obvious strata behavior is.According to the energy characteristics analysis of serious strata behavior, it reveals that strong strata pressure is caused by the combined effects of instability of huge structure, side abutment pressure of gob, working face advance abutment pressure and Jurassic coal mining pillar stress transmission. |
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