Study On The Top-coal Fracture Condition And Mechanical Properties In Fully-mechanized Top Coal Caving Mining

Fully mechanized top coal caving mining is a main mode for thick coal seam.The recovery rate is depend on evolution of top coal medium in fully mechanized top coal caving mining.Compared with other methods,the mechanism of conversion for top coal medium is vague,state of top coal medium will transform to discontinuous and discrete from continuous,and the theory need to be enhanced.A complex mechanical system generated in strata-top coal will be imbalanced and destroyed,mine pressure need to be revealed in fully mechanized top coal caving mining.With help of similar material experiment of full-mechanized top coal caving mining,mine pressure monitoring in situ,acoustic characteristics test of top-coal,acoustic characteristics test for coal under uniaxial compression in laboratory and photoelastic experiments,law of evolution for mine pressure and top coal medium can be elaborated in full-mechanized top coal caving mining,characteristics for evolution of force key-force chain in can be revealed.For the characteristics of top coal medium,a dimensionless quantities of acoustic-fracture degree is proposed to divide the top coal medium stages.The theory for a strain-constitutive equations based on acoustic-fracture degree is established to describe the evolution of top coal in fully mechanized top coal caving mining.The main achievements of research are listed as follows.(1)Characteristics for evolution of top coal medium is analysis quantitatively in fully mechanized top coal caving mining.Evolution of top coal medium can be discerned preliminarily by similar material experiment of full-mechanized top coal caving mining.Top coal medium monitoring in situ is carried out and acoustic characteristics test for coal under uniaxial compression in laboratory,it can be divided into five stages of destruction,exiting destroyed,partly destroyed again,penetrating destroyed,cataclasticing destroyed and fluidity destroyed.(2)A strain-constitutive equations based on acoustic-fracture degree can be established.Contrapose top coal medium evolution in fully mechanized top coal caving mining,acoustic characteristics test for coal under uniaxial compression in laboratory and combined with strain-constitutive equations,a fracture constitutive relation unified can be proposed.(3)Bonding strength and contact stiffness of particles play an important role in disintegration of coal particles cluster.Compressive strength of cluster depend on bonding strength and friction coefficient of particles,degree of disintegration for cluster depend on contact stiffness.(4)Evolution of force chain is the key factors for mine pressure in fully mechanized top coal caving mining can be revealed.The evolution of force chain system in strata-top coal can be described qualitatively in different assembles by photoelastic experiments.(5)The evolution of force chain system in strata-top coal can be described quantificationally.Force chain in stope when photoelastic experiments carried out can be extracted quantificationally by computer technology.It is that the sedimentation law of strata and characteristics evolution of arch in strata-top coal can be described in fully mechanized top coal caving mining,the relation between pressure in top coal and mechanical system of force chain in stope can be revealed.The internal relations between evolution of mine pressure and mechanical system of force chain in stope can be clarified.