Top-coal Caving Law And Top-coal Caving Process Optimization Of Extra-thick Coal Seam With Dirt Bands In Complex Stress Environment

The low top coal release rate of fully-mechanized caving mining in extra-thick coal seams is a problem that has always existed in fully-mechanized caving mining technology.In particular,extra-thick coal seams are prone to contain extremely complex dirt bands layers,which is not conducive to the normal caving of top coal,thus exacerbating the above problems.Therefore,how to improve the recovery rate of fully-mechanized caving mining in extra-thick coal seam has become a difficult point to be overcome.This thesis takes the 13#rich dirt bands thick coal seam of Shaping Coal Mine as the research object,and studies the top coal caving law and the optimization of caving process parameters of the rich dirt bands thick coal seam.The specific results are as follows:（1）The general situation of 13#extra-thick coal seam with rich dirt bands in Shaping Coal Mine is preliminarily analyzed.It is determined that there are extremely complex partings in top coal and mining problems under different stress environments in 13#extra-thick coal seam with rich parting.The physical and mechanical parameters of coal strata in 13103 fully mechanized caving face are tested,and the physical and mechanical parameters of coal strata are obtained,which provides data support for subsequent research.（2）The occurrence of dirt bands in 13#extra-thick coal seam with rich dirt bands is classified.The analysis shows that the top coal can be broken in advance under the action of advance abutment pressure of working face,but the dirt band cannot be broken in advance.Therefore,the structural mechanics model of dirt band cantilever beam is established.The distribution law of bending normal stress in dirt band under the action of mine pressure and hydraulic support support resistance is analyzed,and the calculation formula of critical thickness of dirt band breaking is obtained.The UDEC simulation is used to obtain the top coal caving law of the extra-thick coal seam with rich dirt bands under the influence of different dirt band thickness,number of layers and layers.According to the difficulty of top coal caving,it is proposed that when the top coal contains a single layer of median dirt bands and the thickness exceeds 1.0 m or there are more than three layers of dirt bands in the top coal,and the thickness is greater than or equal to 0.5 m,corresponding measures should be taken to break the dirt bands in the top coal in advance or reduce the strength of the dirt bands,so as to solve the problem that the top coal is difficult to caving under the influence of dirt bands.（3）In order to explore the caving situation of top coal in extra-thick coal seam with rich dirt bands under goaf,FLAC^3D and UDEC were used to simulate and study the stress evolution law,plastic zone development law and top coal caving law of extra-thick coal seam with rich dirt bands under different stress environments.It is concluded that the top coal with rich dirt bands under solid coal is difficult to caving,and the top coal caving degree of extra-thick coal seam with rich dirt bands under goaf increases but the block degree is larger after the dirt band is broken.（4）On the basis of the above research,PFC^2D is used to study the influence of different coal drawing process parameters on top coal drawing under different stress environments.By comprehensively comparing the top coal drawing rate and dirt bands content,the coal drawing process parameters of fully mechanized caving mining under goaf and solid coal are optimized.In the fully mechanized caving mining under the solid coal,the reasonable caving process parameters are the cyclic caving step distance of 1.6 m,the mining and caving ratio of 1:3.3（mining height of 4 m）and multi-round sequential caving.In the fully mechanized caving mining under the goaf,the reasonable caving process parameters are the cycle caving step distance of 0.8 m,the mining and caving ratio of 1:4.7（mining height of 3 m）and the single round interval caving.（5）According to different multi-round coal caving methods,the field measurement is carried out.The measured results show that the top coal caving rate of multi-round interval coal caving is 79%,while the top coal caving rate of multi-round sequential coal caving is 85%～87%,and the top coal caving rate of multi-round sequential coal caving is the highest.The results of numerical simulation are verified.There are 60 figures,12 tables and 81 references in this thesis.