| With the development and perfection of expressway network in China,the construction of long and long expressway tunnels will inevitably pass through unfavorable geological areas in goaf of coal seam.Under the disturbance of tunnel construction,the geological diseases caused by secondary deformation of old goaf are the key problems that must be faced in the process of new tunnel construction.Based on the Zhangjitun Tunnel Project of Erlongguan(Yunnan-Guizhou Provincial Boundary)to Zhenxiong County Expressway,and on the basis of extensive investigation of the mined-out area of Zhangjitun Tunnel Coal Mine,the deformation law,mechanical behavior and construction control technology of the tunnels in the mined-out area are thoroughly analyzed by means of numerical simulation,and the following results are obtained:(1)The distribution,occurrence and characteristics of the old goaf in the tunnel site area are determined,and the surrounding rock properties of the goaf are systematically expounded,and the surrounding rock of Zhangjitun tunnel is divided.(2)According to the displacement criterion,a criterion for determining the stability of surrounding rock of tunnels in overburden inclined goaf section(i.e.,monitoring displacement value is not greater than the limit displacement of tunnels)is proposed to establish the boundary value of the length range of the area strongly affected by overburden goaf section on tunnels;the displacement of tunnels in underlying goaf section is synthetically proposed to evaluate the structural stability of highway tunnels according to the deformation control index of tunnel pavement structure.Indicators(tunnel bottom sag value)and relevant specifications are combined to give the boundaries of the length range of the strongly affected area.Considering the effect of inclined goaf on tunnel in space and longitude,a three-dimensional numerical calculation model of 25 inclined goaf tunnels is established.The final vertical displacement of characteristic points of arch roof and arch bottom along tunnel depth is extracted.The boundary value of strongly affected area of tunnel is extracted based on the criteria for dividing the strongly affected area of overlying and underlying inclined goaf.The data are fitted and analyzed by MATLAB.Under the influence of two factors of mining height D and intersection angle,the length variation law of the tunnel in goaf section strongly affects the area.(3)According to the actual construction conditions of the tunnel,through numerical calculation method,the calculation models of CD method,CRD method and step method for circular excavation and support are established respectively,and the variation laws of the principal stress and displacement around the tunnel under different excavation and support modes are analyzed.Through comparative study,it is concluded that during the construction of the tunnel in the goaf section,CD method and CRD method are used to excavate and support the tunnel safety.Considering the factors of economy and complexity of working procedure,CD method is selected to construct the fractured surrounding rock in goaf.(4)According to the research on the construction control technology of inclined goaf tunnel,it is concluded that the treatment measures of advance small conduit plus CD excavation support method are reliable and effective in the construction of overlying inclined goaf section,and the improvement effect of grouting reinforcement measures of underlying inclined tunnel basement is obvious in the strong influence area of underlying inclined goaf of Zhangjitun tunnel.Through numerical simulation,the influence of coal pillar activation in goaf beyond the strong influence area on tunnels above the roof of goaf is analyzed.It is concluded that the whole tunnel subsides after horizontal goaf activation in cross-section,and shear failure of surrounding rock occurs at the arch waist.Therefore,the activation of goaf outside the strong influence area has certain influence on the structural safety of existing tunnels,which needs to be strengthened in the construction process.Structural strength. |
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