| Longwall top-coal caving mining has the advantages of low mining cost,strong adaptability to changes in geological conditions,high yield and high efficiency,and has become one of the main methods of thick coal mining in my country.Scholars at home and abroad have carried out a lot of theoretical and experimental research on this mining technology,and have achieved fruitful research results,but further exploration is needed in the top-coal drawing ratio and the cooperation of procedures and equipment.First of all,it has the problem of relatively low recovery rate;therefore,it is necessary to clarify the flow and drawing law of the top-coal above the support after crushing.Based on this law,guide the selection of coal caving technology and the determination of the criterion for stopping the caving,so as to improve the working face recovery rate and reduce the refuse content;secondly,the technology of longwall top-coal caving mining is complicated,and it is necessary to carry out research on the time-space coordination relationship between the procedures and the equipment,so as to make the coordination of various procedures more closely and give full play to the production capacity of the equipment.This thesis takes the 12309 working face of Wangjialing Coal Mine as the engineering background,through limit equilibrium theory studies the mining stress field evolution law of top-coal,reveals the stress state and caving mechanism of the top-coal in the stress field,and conducts on-site measurement of top-coal caving block size.Based on the measured top-coal caving block size,the discrete element particle flow code(PFC)was used to establish a numerical model of loose coal caving,and the dynamic evolution law of top-coal boundary and the morphological characteristics of draw body are explored.Based on the above research,a numerical simulation experiments with different combination of technology parameters were designed,and the study was carried out research on the top-coal loss rule in multiple drawing cycles,clarified the influence of different coal caving technological parameters on the top-coal drawing effect.A reasonable coal caving technology parameters and criterion for stopping the caving suitable for 12309 working face are determined.According to the obtained reasonable coal caving parameters,using the method of theoretical analysis,the time-space coordination relationship between longwall top-coal caving mining procedures and equipment is studied.(1)The expression of the abutment pressure distribution in the plastic zone and elastic zone of the longwall top-coal caving stope is deduced,and the distance between the peak point of the abutment pressure and the coal wall is 14.8 m,and the influence range is 44.3 m,and the distribution curve is drawn.The top-coal caving mechanism is analyzed in combination with the Mohr stress circle,according to the on-site measurement of the top-coal caving block size,the average mass percentages of the top-coal blocks with a particle size of4.0?9.2 cm,9.2?14.4 cm,14.4?19.6 cm,19.6?24.8 cm,and 24.8?30 cm are 18.96%,32.64%,23.47%,12.53%,12.40%,respectively.Through the statistics of the number of drawing blocks of different size,the law that the number of drawing blocks gradually decreases as the block size increases.(2)The dynamic evolution law of top-coal boundary during initial drawing process and periodic drawing process is studied.Marking points were set to analyze the trajectory and speed of coal gangue at different locations in equal time intervals,and the parabola was used to describe the shape of the top-coal boundary.Through inversion of the draw body,it is found that for the initial draw body and the periodic draw body when the coal drawing time is long,the overall shape is an ellipsoid whose lower part is cut by the support shield beam.The periodic draw body when the coal drawing time is short is similar to the sudden collapse of the loose body.(3)Designed 9 sets of numerical simulation tests with different top-coal caving thickness and top-coal caving step distance,the flow difference and loss rule of top-coal in multiple steps are statistically obtained,and the coal loss is classified into three forms according to the loss rule,and the mechanism of the three forms of coal loss are elaborated separately.The influence of top-coal caving thickness and top-coal caving step distance on the coal drawing effect of each step,such as top-coal output at each step,the aggregates of drawing coal gangue particles,the shape of the residual coal in the goaf,and the amount of residual coal at different loss locations,are respectively studied.Under the premise of considering the coal cutting recovery rate,the reasonable coal caving technological parameters suitable for the12309 working face are determined to be 3 m top-coal caving thickness and 0.8 m top-coal caving step distance,the coal seam recovery rate is 87.51%.(4)Considering the relationship between adjacent steps of drawing coal,the excess coal draw body was inverted and divided into 4 partitions,and the research was carried out around the proportion of each partition and the location of the releasable residual coal.Among the top-coal particles discharged from coal,only about 1/3 of the particles are releasable residual coal that can be released from excessive drawing top-coal,and based on the low refuse content and high recovery rate,the criterion for stopping the caving suitable for the actual production of the 12309 working face is proposed as "seeing the gangue and closing the window".(5)Explained the coordination relationship of various procedures and the coordination relationship of equipment in longwall top-coal caving mining.According to the reasonable coal caving technological parameters of the 12309 working face,the coal cutting speed,the coal drawing speed and the reliability of the coal cutting-moving frame system of the shearer were studied respectively,and the load-bearing coordination relationship of the front and rear scraper conveyors was determined. |
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