Study On The Mechanism Of Coal Wall Spalling And Control Of Large Mining Height Longwall Face In Shallow Coal Seam

The fully mechanized mining technology with large mining height is the main mining method of shallow buried thick seam in Northern vegion of Shaanxi.The production of the longwall face has been constantly increased with,the increase of mining height,and the problems such as spalling and roof falling are highlighted,which has become a difficult problem to be solved urgently for large mining height mining technology.This article takes the spalling of longwall face as the research object,based on the measured data of pressure characteristic of longwall face,through physical simulation,theoretical analysis and numerical calculation,the interaction relationship between "roof-coal wall-support" and the spalling mechanism of longwall face is researched,and it can provide theoretical basis for spalling control.Through the study of physical simulation,it is obtained that the maximum spalling depth is located at the upper of coal wall during the periodic roof weighting.The preact fracture of roof and the rotary subsidence are the main factors of the instability of the longwall face.Besides,the interaction relationgship between supports and the coal wall is verified,due to the poor capacity of hydraulic supports,the coal seam bears great roof pressure,so the spalling happens,and the instability coal wall also has an adverse effect on contact and control between supports and roof.Based on the Winkler elastic foundation theory,the mechanical model of roof breaking structure is established,through theoretical analysis,the instability mechanism and process of coal wall under the condition of large mining height is revealed,the roof deflection curve equation is set up,besides,the extremity bearing pressure formula of coal wall is worked out,the discriminant condition of the stability of the coal wall is determined.Based on the research above,five significant factors are selected,which are mining height,internal friction angle,cohesive force,elastic modulus and advancing speed,using UDEC numerical simulation software,the influence of factors on coal wall spalling is analysed,and the law of coal wall spalling under the impact of the five factors is explored.The study of the "roof-coal wall-support" system in the longwall face shows that the proper support resistance can reduce the load of coal wall effectively.improving the proportion of setting load to the rated working resistance properly can help to accelerate the increased speed of support resistance,it can reduce the roof subsidence,coal wall horizontal displacement and plastic failure zone effectively,thus it can reduce the occurrence probability of spalling and the degree of coal wall spalling.Finally,based on the spalling control,the mechanical model of roof structure is established,and the calculation formulas of reasonable setting load and the support resistance are given out.