Morphological Characteristics Of Mining Fractures And Their Dynamic Response In The Process Of Stress Recovery

Affected by mining overburden will produce mobile and breakage,by a large number of gas desorption mining in release near the fracture zone,the research of mining overburden rock fracture distribution and development for mine gas extraction system provides the theoretical basis,especially the complex geological conditions of coal mine in China now,the study of mining-induced fracture distribution and development characteristics of overburden rock is very necessary.In this study,uniaxial compressive,uniaxial tensile,and uniaxial direct shear tests were conducted on fine grained sandstone,medium grained sandstone,coarse grained sandstone,and limestone respectively to analyze stress-strain curves,mechanical parameters,failure forms and fracture development of specimens,three-dimensional reconstruction of fracture surfaces of specimens and quantitative analysis of characteristic parameters of fracture surfaces.In addition,FLAC^3D numerical simulation software was used to conduct numerical simulation on the fracture specimens obtained by taking the height,Angle,contact area and filling degree of the fracture surface of the fractured rock mass as the characteristic parameters.A mechanical constitutive model was constructed and the fracture morphological response characteristics during the stress recovery process were obtained by combining with the mechanical description of stress recovery.The following conclusions were obtained:?1?In the case of uniaxial compression,rock failure is mainly manifested as shear failure,split failure,irregular rock shape,and serious rock peeling during the failure process.The stress distribution is uneven mainly due to the heterogeneity of the rock itself and the different cementation degree of filling in the rock.Rocks under the condition of uniaxial tension,the tensile fracture of the rock location is random,but is close to breaking point occurs from the rock face is more,the position of rock tensile has no obvious peeling phenomenon,when rock with radial stratification,often split occurred in the bedding,when rock containing axial bedding,fracture have larger gap.In the case of uniaxial direct shear of rock,only one crack is connected to the whole specimen when the rock is fractured,which is similar to the uniaxial tensile test.The fracture on the pressure surface is relatively straight,while the fracture on the horizontal plane is more circular.?2?Based on FLAC^3D numerical software,the effects of meshing degree of fractured rock mass and filling degree of gap surface on stress recovery process are simulated.Under the condition of the same load and the same height and angle of the cusp,when the point angle is 30°,45° and 60°,stress concentration phenomenon will occur in the contact area of the cusp.When the point Angle is larger,the contact area of the cusp will be larger,the bearing strength will be larger,and the damage degree will be smaller.Under the condition of the same load and different height of the apex angle,the stress concentration area also appears in the apex contact area when the height of the apex is 1cm,2cm and 3cm.The higher the height of the apex,the smaller the contact area of the apex area is,and the more prone to plastic failure.In the case of the same load,the same angle and height of the tip,but different contact area of the tip,the stress concentration area is on both sides of the contact area of the tip.The larger the contact area of the tip,the stronger the bearing capacity of the specimen.For filling degree 15%,25%,35% of the situation analysis,stress,high had occurred in filling block in the middle of the area,in the same load conditions,the same filling degree,limestone as a filler block pressure on the performance of the strong,the coal rock as filling block pressure on the performance of the weakest,under the same load,under the condition of the same lithology filling block,with the increase of filling degree,the pressure on the performance is enhanced.