Study On Key Problems Of Roadway Caving Mining In Steep Medium-thickness Seam

There were the mainly four key problems on roadway caving mining method of steep inclined medium-thickness seam, which were top coal falling capability and its evaluation, caving roadway layout and maintenance, the top coal broken mechanism and process parameters.Based on the industrial tests of seveal mines, top coal falling capability was analyzed and evaluated by the gray system theory and fuzzy mathematical method. The correlation of indicators and the top coal falling capability is also analyzed and calculated with 12 second indicators and 7 natural indicators. The indicators were seam strength, mining depth, seam thickness, seam dip angle, the roof and floor rock strata, sandwiched rock and safety conditions etal, subdivided in the following order: seam strength,seam dip angle, seam thickness, mining depth, sandwiched rock, safety conditions and the roof and floor strata. Meanwhile, the top coal falling capability is divided into five categories by calculated and comparatived : falling capability good (â… ), falling capability better (â…¡), falling capability fair (â…¢), falling capability poor (â…£), up poor (â…¤). The top coal falling capability can be judged by these indicators.Top coal stress environment and deformation is analyzed by elastic-plastic theory and its simulation software (FLAC). The result shows that the main force of top coal from gravity of top coal and concentrated stress of roof. Meanwhile, the level stress and methane pressure on the top coal to broken coal play a major role. The calculated height of limit equilibrium is consistented with field test data of deep displacement. The limit balanced height of top coal stress top is relevanted with coal caving. The more carshed the broken and caving of the top coal is, the more increased the limit balance height increases. Insteadly, the top coal broken and caving is good with limit equilibrium height decreasing. Stress and displacement of caving roadway and caving chute construction disturbance is simulated by FLAC software of numerical model. The plastic area and plastic damage of caving roadway and caving chute appeared in the roadway shoulder and support-foot-binding is caused by construction disturbance. Displacement trace and main stress of roadway rock will be conducive to the top coal broken.According to the top coal broken mechanism, the broken process of top coal and main factors of top coal caving are analysied by plasticity theory. Top coal broken along the direction of coal seam is because of the tensile stress of central part of the top coal over the tensile strength of coal. Top coal broken is represented as a process of "falling-shift fracture belt-new falling-fracture zone further upward". Top coal broken is greater relevaned with coal mechanical properties and the joints and fractures. Caving deformation and broken process along the dip direction of coal seam are numerically simulated by non-continuum theory and simulation software (UDEC). The broken process and space shape of the top coal crusher deformation along dip of coal seam are analyzed. Space shape of the top coal with arch form, or the formation of a "roof-seam-floor" asymmetrical mechanical arch structure, vault of caving arch to shift direction of coal seam roof. The destruction process of top coal and rock can be divided into four zones. They are the top coal caving area, slide area along the bottom of floor, damaged area of roof separation,coal and rock falling area backward. Deformation of seam roof and floor is small and mostly falling to the caving roof and floor rock as a supporting role.the catastrophe theory is used to analyse the study of top coal broken mechanism. Top coal is destructed by weak of joints and fissures. The cusp catastrophe model of top coal instability is established by the catastrophe theory and reached the criterion of top coal caving that is ratio of stiffness of top coal fissures plane elastic nucleus medium and stiffness of yield zone medium, which is stiffness ratio. When the stiffness ratio is less than 1, the smaller top coal elastic nucleus medium stiffness show, the greater the yield stiffness, more prone to mutation top coal crusher slip instability.Based on the drawing theory of computer simulation to produce top coal process parameters are optimized in order to enhance the top coal recovery rate and to decrease top coal gangue rate. The recent levels is moving down on contact of top coal and gangue by caving orders . Sublevel height and thickness of the coal seam is correlated. Seam thickness increasing decreases sublevel height. Caving chute distance and top coal recovery are closely related. Smaller the distance , higher top coal recovery rate. The gangue of the modest increasing in the amount can increase the recovery rate of the topcoal.The key problems was studyed on roadway caving mining method of steep inclinedmedium-thickness seam. It is of practical and theoretical significance in application and dissemination of the mining method.