Study On Bearing Characteristics Of Support Structures And Surrounding Rock Stability Of Deep-buried Highway Tunnels Passing Through Complex Goafs

Coal resources have always been an important source of energy in China.With the constant exploitation of coal resources in China,many coal mining goafs of varying sizes and distributions have been formed.In recent years,with the development of the strategy for the western development of the country and the strategy for the rise of central China,China has With the rapid development of the traffic network system,the construction of expressways and high-speed railways is changing with each passing day.This will inevitably involve the issue of highway tunnels or railway tunnels passing through various complex distributions of goafs during the construction process.This article relied on the tunnel project of the Zengjiashan Expressway.There are many large coal mines and many privately-mined small coal mine goafs in the tunnel area of the project,which poses a huge potential safety hazard for the tunnel construction.In this paper,through the methods of numerical simulation,on-site monitoring and geological radar detection,a systematic study on the stability of surrounding rock and the bearing characteristics of the structure through the tunnel in the goaf zone under complex geological conditions has been carried out.The main research work and achievements of this paper are as follows:(1)The field monitoring and tunnel excavation reveals that the surrounding rock of the tunnel entrance and exit faces are broken and there are several horizontal coal lines on the face of the tunnel body.The upper and lower coal seams are well developed,and the fracture water is relatively developed.There are water seepage phenomena in the surrounding rock and the face of the rock,and the surrounding rock conditions are poor.Combined with the measurement results of the displacement of the surrounding rock,the deformation law of the surrounding rock after excavation of the tunnel is revealed.Through on-site geological radar detection,the spatial distribution characteristics of the small kiln goaf in the detection area were revealed.(2)The 3D numerical simulation calculations were carried out by taking account of the spatial distribution characteristics of the local topography and goafs.From the aspects of the construction process and the settlement of the tunnel,the stability of the surrounding rock,the initial supporting force law and the structural safety factor,etc.The influence of the goaf of the large coal mine in Zengjiashan on the tunnel surrounding rock and support structure during and after construction.(3)Using 2D planar elasto-plastic simulation,the small kiln mining zone is located along a 90° directly above the tunnel,45° diagonally above,0° above the horizontal plane,-45° below the inclined plane,and-90° below the tunnel.Change of hole diameter and net distance in open space,development of plastic zone in surrounding rock of tunnel,displacement of surrounding rock and change of carrying capacity of supporting structure.(4)The finite element strength reduction method was used to study the influence of the mined-out area of small kiln on the construction of the tunnel,and a model for assessing the degree of impact was established,and the degree of influence of the spatial distribution of the mined-out area of the small kiln on the stability of the tunnel was evaluated.In general,the results show that from the perspective of net distance,the degree of influence decreases with increasing net distance;from the perspective of hole diameter,the degree of influence decreases with the increase of the diameter of the goaf;from the position distribution From the angle,the goaf above the tunnel has a greater impact than the below goaf.