Study On The Impact Of Dynamic Load In Fully Mechanized Top Caving Faces Of Shallow Thick Coal Seam Under Various Extraction-drawing Ratio

The overburden roof of the shallow thick coal will be instantly fractured and instability after being disturbed by mining in working-face,this will cause the coal-rock to be in a responsive state of superposition of dynamic-static loading in front of the working-face and be susceptible to induce dynamic disasters.With the development of coal mining technology and equipment,it demands higher requirements on the technology of full mechanized top caving faces,especially for shallow thick coal seam with shallow burial,thin bedrock and thick loose-loaded coal seam geological condition.The study was based on the stability of the overburden roof and the coal wall in front of the workings-face in the shallow thick coal seam.The simulation experiments,numerical calculations,field monitoring and validation of theoretical calculations were adopted.It profound studies on the spatial structure evolution characteristics of overburden roof of the shallow thick coal seam and the influence of overburden broken position under various extraction-drawing ratio.The overburden destabilization mechanism of the shallow thick coal seam,dynamic loading effect,and the characteristics of the dynamic loading effect of the different broken positions under various extraction-drawing ratio was analysed.Finally,the dynamic loading responsive law of full mechanized top caving faces under various extraction-drawing ratio was revealed.The first weighting interval and overburden evolution process of overburden roof of the shallow coal thick coal seam was obtains;It analysed the characteristics of the peak of the advance supporting stress and the law of the distance between the peak and the coal wall various extraction-drawing ratio.It determined the intrinsic correlation between the advance supporting stress and the roof breakage location.The dynamic loading theory of fractured and instability of overburden roof was invoked,the principal factors which influence the discrepancies in dynamic loading stress amplitudes at breakage instability in shallow thick coal seams were identified,the non-linear relationship between the main factors and the amplitude of the dynamic loading stress was also analysed,The interrelationship among the magnitude of dynamic loading stress amplitude,the broken position of overburden roof and coal seam thickness was analysed by the theoretical,the intrinsic correlation between dynamic loading stress amplitude and various extraction-drawing ratio was obtained.Based on the full stress-strain responsive characteristics of coal-rock under dynamic load,the responsive characteristics of the coal-rock for different dynamic load was analysed.it obtained the dynamic load stress-time curves for different breaken positions with various extraction-drawing ratio,the difference characteristics and the correlation with the stress-time curves,Ultimately,it was shown that there is a significant correlation between the magnitude of dynamic loading stress for various extraction-drawing ratio.The characteristics of the propagation of the dynamic load on the full mechanized top caving faces and the whole responsive process of the broken overburden roof under small extraction-drawing ratio was analysed.Based on the concept of "disturbance intensity",it revealed the characteristics of disturbance intensity of the full mechanized top caving faces under various extraction-drawing ratio,the influence on the fracture pattern of the overburden roof was shown for various extraction-drawing ratio,it resulted in synchronous variability in the response to dynamic load the full mechanized top caving facesThere are 48 pictures,9 tables,and 121 references.