Deformation Mechanism And Control Of Surrounding Rock Structure In Thick Loose And Extra Thick Coal Seam

With the westward shift of China’s energy strategy,coal resources are further developed to the intensive and efficient production mode of large-scale coal bases in the West.The enrichment of thick coal seam resources in Western China provides favorable conditions for the centralized mining of large-scale coal bases.However,the typical geological conditions of thick loose layer,extra thick coal seam and thin bedrock are easy to derive disasters such as severe ground pressure,serious damage to surface environment and frequent occurrence of air leakage and fire pose a severe challenge to the safe and efficient production of large-scale coal bases in Western China.Therefore,surrounding rock deformation mechanism and control of fully mechanized top coal caving face in western shallow buried thick loose seam and extra thick seam have become one of the major key scientific problems to be solved urgently.By means of laboratory test,theoretical analysis,field measurement,similarity simulation,numerical calculation and field test,this thesis makes an in-depth study on the scientific problems of fully mechanized top coal caving face in thick loose and extra thick coal seam,such as ground pressure behavior law,roof structural characteristics,load transfer mechanism,structural optimization method and surrounding rock control technology.The main research work and innovative achievements are as follows:（1）The constitutive model of unloaded coal is established,the unloading mechanical behavior of coal in the process of top coal caving is quantitatively characterized,and the influence laws of parameters such as moisture content and brittleness index on the stress-strain relationship of unloaded coal are obtained.（2）The periodic evolution mechanical model of the basic roof structure of thin bedrock,thick loose layer and extra thick coal seam is established,the multi parameter critical control equation of the structural catastrophe of the roof along the strike of the working face is deduced,the influence laws of the variables such as fracture block degree,rotation angle,breaking angle,friction coefficient and corner extrusion coefficient on the"rotation-sliding"stability of the roof are obtained,and it is clear that the block degree,rotation angle and breaking angle are the main control parameters of the structural catastrophe of the roof.（3）The structural analysis model of gob side roof adjacent to fully mechanized top coal caving face in extra thick coal seam is constructed,and the instability criterion of"bending breaking"under the limit equilibrium state of gob side roof is determined;The coupling dynamic equilibrium differential equation of support surrounding rock under the multi factor action of mass and displacement of key block C,stiffness and damping of lower broken coal and rock mass,stiffness and displacement of hydraulic support is solved,and the coupling relationship between key block C,lower broken coal and rock mass and support load of hydraulic support is clarified.（4）The discrete element calculation model of fully mechanized top coal caving mining in thick loose layer and extra thick coal seam is established,the spatial dynamic evolution law of"large structure"of roof in the mining process of fully mechanized top coal caving face in thick loose layer and extra thick coal seam is analyzed,the deformation characteristics of roof in different layers and the transformation mechanism of bending-breaking structure are revealed,and the quantitative relationship between the evolution of roof structure and the mining influence range is determined.On this basis,the control principle of roof structure in the advancing process of fully mechanized top coal caving face in thick loose seam and extra thick seam is put forward.（5）The similarity test model of fully mechanized top coal caving face in thick loose bed and extra thick coal seam is constructed,and the influence of the length of non caving section at the end of fully mechanized top coal caving face on the inclined roof structure of the face is studied.The evolution law of the key parameters such as the"large structure"hanging length,breaking shape and rotation angle of the roof on the goaf side of the adjacent roadway with the length of the non caving section at the end of the working face is determined;The mechanical response law of"small structure"of section coal pillar and end surrounding rock under the active action of"large structure"of roof is clarified.The structural optimization method of pre splitting and roof cutting at the end of fully mechanized top coal caving face in thick loose seam and extra thick seam is put forward.（6）This paper reveals the dynamic evolution characteristics of section coal pillar stress,ground pressure behavior law of working face and roof load transfer mechanism during the advancement of fully mechanized top coal caving face in thick loose layer and extra thick coal seam.The secondary development of FLAC^3D is carried out,and the constitutive equation is embedded into the calculation model to reasonably describe the mechanical behavior of the surrounding rock at the lower end under the unloading effect of top coal caving mining.The influence laws of the length of the non caving section and the size of the section coal pillar on the energy density of the coal pillar,the stress distribution of the surrounding rock at the end and the load transfer path of the top plate are obtained,It can be used as the optimization basis for the length of non caving section and the size of coal pillar at the end of fully mechanized top coal caving face in thick loose and extra thick coal seam.（7）Based on the design principles of key parameters obtained from theoretical analysis,numerical simulation and experimental research in this thesis,an integrated technical scheme of surrounding rock control in fully mechanized top coal caving face with thick loose layer and extra thick coal seam is proposed,which is centered on the technologies of full caving at the end,directional weakening of roof,removal of roadway support behind the face,optimization of section coal pillar size and so on.The successful implementation of the technical scheme verifies the rationality and practicability of the research results of this thesis.There are 137 figures,23 tables and 289 references.