The Movement Laws Of Overburden And The Response Mechanism Of Foundation Under Dynamic Load In Mining Of Shallow Buried Multi-coal Seam

After coal is mined,a large number of subsidence areas are left on the ground,especially in Shanxi,Inner Mongolia,Shaanxi,Henan,Shandong,and other provinces,where coal resources are abundant,subsidence areas are widely distributed and with a large number and rapid growth.However,with the rapid development of High-Speed Railway(HSR)in China,the construction and planning of HSRs inevitably cross the subsidence areas of coal-production areas.This thesis is based on the practical problems of the construction project of HSR crossing goaf sites,combined with the geological conditions of Majiazhuang coal mine near the Tai-Jiao HSR.Using theoretical derivation,physical model tests,numerical simulation,and on-site monitoring data analysis,to study the movement laws of Shallow Buried Multi Coal Seam(SBMCS)overburden and the foundation response mechanism under the dynamic load of HSR.The main work and achievements of the research are as follows:(1)Based on rock mechanics theory and key strata theory,and combining with physical simulation test and numerical simulation,a mechanical model of overburden collapsed in mining of SBMCS was established.The mechanical structure of overburden failure in mining of SBMCS was clarified,and the movement laws of overburden in mining of SBMCS was studied.(2)Through physical simulation tests and numerical simulations,the collapsed structure of overburden in mining of SBMCS was studied,and the characteristics and laws of overburden and surface damage in mining of SBMCS were elucidated.The vertical manifestation of overlying rock failure in mining of SBMCS is characterized by "two zones",the subsidence of the overburden is manifested as cumulative subsidence at multiple levels,the surface subsidence curve manifested serrated,and the surface tilt and horizontal movement curve is characterized by abrupt changes in cliff shape.(3)The characteristics and laws of overburden cracks development were revealed,and the relationship between fracture development and coal seam thickness and burial depth was analyzed.The vertical and horizontal fractures in the overburden in mining of SBMCS are interconnected,forming a 3D network structure that runs through the goaf of each coal seam and directly connects to the surface.The vertical development spacing of cracks exhibits a periodic distribution pattern.(4)Based on 30 numerical simulation models,the relationship between overburden and surface damage with coal seam mining thickness,burial depth,and the ratio of coal seam burial depth to mining thickness,(RDT)of coal seam,was analyzed.A new calculation method for RDT in mining of SBMCS is provided.The RDT equal to 15 is the boundary between the two states of overburden failure.(5)Based on the residual deformation mechanism,combined with physical model tests and numerical simulation,the characteristics and laws of overburden residual subsidence in mining of SBMCS were analyzed.In similar simulation experiments,Digital Image Correlation(DIC)technology was used to observe residual subsidence of overlying rocks and surface,improving the efficiency and accuracy of experimental data observation.(6)Based on the analysis of HSR’s dynamic load,a similarity simulation test method for HSR’s dynamic load was established,and the propagation and attenuation laws of vibration in the foundation were analyzed.The dynamic load in the form of a sine wave was applied to the model.The movement,deformation,and stress response of the foundation under different positions,widths,and amplitudes of dynamic load applied were studied.The response mechanism of the foundation under HSR’s dynamic load was revealed.There are 94 Figures,7 Tables and 213 References in this thesis.