| Protective layer mining is one of the most important and efficient means to prevent and control coal and gas outburst.After the mining of protective layer,the effect of pressure relief gas flow in protective layer is determined by the development and evolution of fractures in the coal-rock mass structure composed of roof and floor of protective layer and coal layer affected by mining.Therefore,it has great significance to study the fracture evolution law of coal-rock mass and the gas unloading migration law by carrying out the experiment of Acoustic Emission characteristics and fracture propagation for coal and rock combination.(1)Based on the geological conditions of the coal seam of Shanxi Heshun Tianchi energy resources co.,LTD.,three different types of coal-rock complex models were extracted,and the similarity criteria of coal-rock complex were deduced as the theoretical guidance.On this basis,the physical and mechanical properties of rock-like and briquette materials with different proportions were obtained through pilot tests.Finally,different types of coal and rock combination has been developed according to the basic parameters of the prototype.(2)Uniaxial compression mechanical properties,acoustic emission characteristics and fracture evolution experiments has been carried out by DYD-10 universal testing machine,the acoustic emission system,the twin clear camera system,and full stress-strain curve and the final failure pattern of coal and rock combination have been obtained.Mechanical change characteristics of different coal and rock combination have been obtained by analyzing mechanical characteristic parameter of 3 kinds of coal-rock combination,such as compressive strength,modulus of elasticity,longitudinal wave velocity.(3)Acoustic emission characteristics has been mainly analyzed for different coal-rock combination under uniaxial stress state based on the results.Five acoustic emission characteristic parameters(transmit ring count,accumulated ring count,energy,accumulated energy,amplitude)have been selected to analyze the relation between stress,fracture development and acoustic emission characteristics under uniaxial compression process and the crack propagation laws of different types of coal-rock combination have been revealed.(4)Full stress-strain curve and crack expansion process of different types of coal-rock combination have been obtained based on the results.Fracture expansion law of different types of coal-rock combination have been revealed by analyzing main fracture characteristic parameters:main fracture extension time,main fracture length,main fracture average expansion rate for 3 kinds of coal and rock combination.Based on the above research,physical simulation method was achieved to prepared coal-rock combination samples by the standardized production processing.Uniaxial compression mechanical properties,acoustic emission characteristics and crack propagation rules of three kind of coal-rock combination were obtained on this basis,which laid a certain foundation for the study of protective layer. |
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