Stability Analysis Of A Metro Crossing Coal Seam Goaf In Guangzhou City

After coal mining,the deformation and failure of the surrounding rock of the mined-out area is caused by the change of the stress state of the underground rock and soil mass,which constitutes a great hidden danger to the safety of the subway tunnel.Therefore,it is of great practical significance to study the stability of subway tunnel running through goaf for preventing safety accidents.This paper is based on the tunnel passing through the coal seam goal in a section of Guangzhou metro.The numerical simulation method is used to analyze the variation law of the instability length of the tunnel and the main factors in the goaf,the stability analysis of tunnel passing through the typical goaf,the comparison and selection of construction methods of tunnel passing through the goaf,and the treatment research of tunnel passing through the typical goaf of instability.The main results are:(1)Based on the geological and goaf data of the study area,the geotechnical layer,hydrogeology,geological structure,coal seam distribution and mining characteristics are elaborated,and the goaf distribution and engineering geological characteristics of the goaf are determined.(2)Numerical simulation software and Origin software are used to analyze the variation rules of the length of the tunnel instability zone,the thickness and inclination Angle of the goaf.The results show that the length of the instability zone of the tunnel has a positive linear correlation with the thickness of the goaf.For the tunnel in the overhanging goaf section,the length of the instability zone decreases gradually with the increase of the dip Angle,and the downward slope of the curve increases first and then decreases.When the dip Angle increases from 30° to 40°,the shrinkage of the instability zone is the most significant.For the tunnel in When the height is 3～5m,the dip Angle of the curve increases firstly and then decreases.(3)When the shield of tunnel reaches the beginning of the interval of a typical goaf,the internal tension failure of A1 standard block and B2 adjacent block is easy to occur;When the shield reaches the central part of the close goaf,serious deformation is easy to occur at the junction of B3 adjacent block and A4 standard block.When the shield reaches the termination side of the interval of goaf,A7 standard blocks are prone to tensile fracture.When the tunnel runs through the goaf,the degree of segment deformation and failure increases.The instability of coal pillar increases the stress release of A1,A2,A5,A6,A9 standard block,B1,B4 adjacent block and K2 capping block,and the degree of deformation and failure is significant.Segment diameter deformation,axis and elevation deviation can not meet the production safety needs,and the tunnel in goaf section is in a state of instability.(4)The numerical software was used to carry out the simulation of tunnel shield passes through under the advance small conduit reinforcement on the overlying goaf and the underlying goaf under the grouting filling,the goaf under the grouting filling respectively,to analyze and determine the optimal construction technology method.The results show that the stress concentration of subway segments is low when the tunnel passes through the mined-out area with grouting filling,and the deformation of segment diameter and the deviation of subway axial direction and elevation all meet the safety requirements,which is a more reasonable construction method.(5)Numerical software was used to simulate the tunnel crossing under the typical goaf with grouting filling,and to analyze and evaluate the stability of the subway tunnel.The results show that in the shield support and operation stages,the stress release degree of segment is low and the mechanical strength of subway segment is large,so the deformation of subway segment belongs to the allowable range,and the subway tunnel in typical control section is in a stable state.It can be seen that the study of subway tunnel through coal seam goaf can master the law of deformation and failure of tunnel surrounding rock and segment,determine a more reasonable construction method of tunnel through goaf,and provide reference for subway to safely pass through coal seam goaf.