Research On Top-coal Medium State Transformation Mechanism And Distribution Shape Of Transformation Interface On Fully-mechanized Caving Face In Steeply Dipping Soft Seam

During the mining process of fully-mechanized caving face,the medium state of top-coal has experienced the gradually degradation process which from relatively complete to highly fragmented,and this process named the top-coal medium transforming process.When the coal is soft,the fragmented mediun state of top-coal will formed front of support,and will easly to falling and cause supports tipping.At fully-mechanized caving stope in steeply dipping soft seam,the asymmetric distribution of mining-induced stress will give rise to the fragmented top-coal formed at different location along the inclined,futher caused the secational distribution of support stability along the inclined.Therefore,the research on the top-coal medium transformation mechanism and the location of transformation interface effected by the mining-induced stress evoulation,and the distribution shape of top-coal medium transformation interface effected by the asymmetric mining-induced stress evoulation of steeply dipping seam,which was helpful to provide scientific basis for support controlling.By the integrated methods of numerical simulation,theory analysis,field monitoring,and physical similar simulation experiment,the top-coal medium transformation mechanism on fully-mechanized caving face and the distribution shape of medium transformation interface in steeply dipping seam has been reaserched,The results indicates that:Under the effects of any factors as homogeneous degree,strength,thickness and load-unload route,the acoustic emission energy release and fracture development both increase sharply at the stage from peak strength to residual strength,and the acoustic emission energy release and fracture development tend to stop after the residual strength,the macro carrying capacity of top-coal failure,when the top-coal enter into the residual strength means it has enter into the medium critical transforming state.There's a positive correlation between original state to medium critical transforming state.Under the real load-unload route of stope,the time-period that the top-coal enter into rethe factors as homogeneous degree,strength and thickness of top-coal and the time last fromsidual strength state was longer than uniaxial compression,and the strain softening after peak strength present stronger ductile character.During mining process,take the location of top-coal macroscopic fractures perforating as boundary,the top-coal form intact to caving has experienced the medium transformation process which form similar continuous to discontinuous.And this process essentially is the process of damage accumulation inside of top-coal.By analysed the internal relations between the "location-deformation-damage-medium state" of top-coal,the progressive deterioration-damage model has been established,and finally realized the quantitative characterization about the relationship between the top-coal medium transformation interface and the coal wall.Effected by the "loading-reduce" function of top-coal the strata behaviors was more mild compared with fully-mechanized mining,and effect by strength and thickness of top-coal the asymmetric and intensity of strata behavior will both tend to change.With the increase of top-coal strength and thickness,the strata behavior will became more violent and the asymmetric characteristics gradual approached to the seam with fully-mechanized mining stope.The final medium state of top-coal above the support is the key influence factor of strata behavior on fully-mechanized caving face in steeply dipping soft seam.The rock structure and stratum horizon in overburden is the main controlling factor of mining-induced stress evolution,and will further function on the medium transformation process of top-coal.The rock structure formed as "voussoir beam" along the strike and formed as "ladder" along the inclined.Effected by the factors as overburden lithology,connecting form of rock structure,caved gangue's nonuniform filling,the stratum horizon of"critical zone" rock structure present the character as gradually transforming.Effected by the gradually transforming of "critical zone" rock structure stratum horizon,the location of top-coal medium transformation interface along the inclined in Changshanzi mine 1123 working face expressed difference.The higher the "critical zone" rock structure stratum horizon was the farther top-coal critical medium transformation interface to the coal wall,conversely,the more nearly.The distribution shape of top-coal medium transformation interface in 1123 working face present as an "asymmetric-triangular" arch.The sectional distribution mechanism of support stability along the inclined effected by the top-coal medium transformation interface has been revealed.The farther top-coal medium transformation interface to the coal wall the worse support stability was,oppositely the better.The technology of top-coal control which take the "improving thickness"and "caving amount sectional controlling" as key points,and the technology of support stability control which take the "working face pseudo-inclined arrangement","optimizing support structure design","normalizing support moving process" as key points has been proposed.