Study On Bedding And Joint Effect Of Coal Impact Tendency

Rockburst is a typical coal mine dynamic disaster.In the existing research on rockburst,more attention is focused on the problem of stress concentration,but there is a lack of further understanding of the origin of coal body.The physicochemical properties of coal and rock mass should be the internal cause of rockburst disaster,and the research on the internal attribute of coal-rockburst tendency should always be the basis of preventing rockburst.Coal is a kind of rock mass with well-developed bedding and joints.There are certain cross fissures in the coal body,resulting in the heterogeneity of coal.The discussion of rock burst needs to transition from outside to inside.In this paper,the relationship between coal bedding and rock burst is taken as the starting point of the research.Through the methods of numerical simulation and experimental research,the relationship between coal bedding,coal fissure existence form,impact tendency and impact failure form is studied.Through RFPA2 D numerical simulation,the influence of fracture inclination on impact tendency and impact failure of coal samples under two different fracture forms of single fracture and cross fracture is studied.Using the universal electronic testing machine in the laboratory to determine the size of each index of impact tendency,calculate its effective impact energy rate,obtain the law of the relationship between impact tendency and bedding angle,compare it with the saturated water content,and systematically and comprehensively analyze the impact tendency of coal.The research conclusions are as follows:(1)The existence of cracks will weaken the compressive strength of coal,but the different effects caused by the change of single crack inclination are not prominent.When the angle between the loading direction and the single crack direction is 90 °,the impact tendency decreases significantly.In the form of cross fracture,the change of fracture cross form and cross dip angle in the same form have a prominent impact on the stress-strain curve.Among the different forms of fracture cross,the horizontal cross fracture form has the most obvious reduction on its compressive strength,followed by the vertical,and the symmetrical form has the least reduction.Under the same crossing form,the uniaxial compressive strength decreases with the increase of included angle,and the minimum value under the same crossing form is obtained at 90 °.Its uniaxial compressive strength shows obvious joint effect.(2)In the form of single fracture,under the dip angle of 30 ° and 60 °,the fracture starts and expands along the original fracture and produces shear failure.The smaller the angle between the fracture and the axial loading direction,the more significant the impact on coal fracture.Under the 90 ° fracture inclination angle,the original fracture bears the vertical axial load,and the crack development depends on the original fracture,but the original horizontal fracture hardly affects the coal fracture.The deformation and failure of coal body are different under different intersection forms of cracks,but they have something in common.There are cracks at the same level as the cross section,which almost does not affect the fracture mode of coal body.If there are vertical cracks,they will penetrate and destroy,showing the main fracture surface.Under the three types of fracture intersection,the change of fracture angle will mostly lead to the early fission of fracture development and the greater degree of fracture development.The fracture development and macro failure show obvious joint effect.(3)The study of acoustic emission diagram shows that with the increase of dip angle in the form of single fracture and the increase of included angle in the form of cross fracture,micro fractures will appear earlier,and the fractures develop slowly,last longer,dissipated energy increases,macro damage degree becomes weaker and impact tendency becomes weaker.When the compressive limit is reached and the macro failure occurs,the acoustic emission is less,the stress release is reduced,and the failure degree becomes weaker,and the conclusion is basically consistent with the macro failure.The number of acoustic emission loading step histogram can directly display the crack development degree and macro failure strength,which has a certain guiding role in judging the impact tendency.(4)Bedding has a significant impact on the impact tendency of bituminous coal.When the loading direction and bedding direction are inclined at 90 °,the impact tendency is the strongest,weak at 0 ° and the weakest at 45 °.Under different bedding,the stress-strain curves of coal samples show significant differences.In the final analysis,the structure is different.It is suggested that the bedding effect should be considered when evaluating the impact tendency of all coal types with bedding.In the practice of coal mining,the influence of stress on the stability of roadway should be considered to avoid that the coal seam bedding is perpendicular to the direction of principal stress in the design of coal pillar.(5)Under the condition of saturated moisture content,the elastic modulus of coal sample decreases,the plasticity increases,the elasticity decreases,and the impact tendency decreases.The impact tendency of the selected coal samples no longer has bedding effect,and the impact index of each bedding coal sample is roughly the same.