Study On Stability Of Tunnel Surrounding Rock In Goaf Based On Coupled Numerical Method

With the increase of highway network in recent years,it is inevitable to cross the strata of coal-bearing goaf.As the left area of coal-bearing strata after mining,the goaf is greatly damaged by the disturbance of coal mining,which makes the goaf area have the characteristics of large porosity,strong dispersion and poor stability of surrounding rock.In this paper,through the strata and the concept of continuous lugu highway in goaf areas appropriate doosan tunnel as the backing,is put forward based on FDM and DEM coupling analysis method,discrete element software PFC3 D and FLAC3 D finite difference numerical simulation to the realization of the software platform,to study under the tunnel in coal-bearing formation in the process of tunnel surrounding rock stability of mined-out area damage characteristics.The main research results are as follows:(1)According to the analysis of the goaf formation strata and goaf formation of discreteness,continuity characteristics of FDM and DEM is presented in this paper,the three-dimensional coupling analysis method,at the same time choose Hoek Brown-strength criterion as the constitutive model,to simulate the tunnel in goaf under formation,and discusses the accuracy and rationality of coupling analysis,and determined the MaoLaDai mesoscopic parameters selection.(2)According to the formation characteristics of goaf,the three-dimensional coupling analysis method of FDM and DEM is adopted to complete the simulation analysis of formation structure and tunnel excavation in goaf,and the dip Angle,spacing and coal mining thickness of goaf are taken as control variables respectively.In the case of no support,the presence of goaf has a greater impact on the stability of tunnel surrounding rock than that of no goaf.In particular,when the tunnel underpasses the double-layer goaf,the goaf has a greater impact on tunnel surrounding rock when the middle zone is smaller.However,the variation of dip Angle,spacing and coal mining thickness of goaf has different influences on the surrounding rock of tunnel.In general,the smaller the dip Angle and spacing is,the greater the coal mining thickness is,the worse the stability of surrounding rock is,and the collapse of surrounding rock is easy to occur in construction.(3)Through coupling numerical simulation,the influence of tunnel support structure on surrounding rock stability when running through single and double goaf is studied,and the surrounding rock pressure borne by lining is analyzed.The radial confining pressure of the side wall of the tunnel side wall and the radial confining pressure of the arch waist are larger than the confining pressure of the arch roof and arch bottom as a whole.When the tunnel undergoes the double goaf,the radial confining pressure of the surrounding rock under the tunnel lining is larger than that under the single goaf.At the same time,the range of loose circle of surrounding rock with and without support is compared and analyzed from two aspects of theory and simulation.The result of theoretical calculation is close to that of numerical simulation at the side wall,but the theoretical calculation is a little small at the vault,which demonstrates the accuracy of numerical simulation.