Study On Anisotropic Seepage Field Characteristics Of Tunnel Fractured Surrounding Rock

After long-term geological action,a large number of discontinuities are produced in the rock mass,including cracks,fault surfaces,joints,etc.Because there are a large number of discontinuities with different geometric parameters in the rock mass,the rock mass has obvious permeability anisotropy.At present,in the analysis of seepage field of mountain railway tunnel,it is generally assumed that the stratum is permeable isotropic.In view of this,based on a single-line tunnel project of Xuyong-Bijie Railway,this paper studies the influence of surrounding rock permeability anisotropy on tunnel structure and stratum by deducing seepage field formula and numerical simulation,and studies the applicable conditions of seepage analysis by establishing two-dimensional random fracture network to solve permeability tensor and the representative element volume(REV),and obtains the following research results :(1)Based on the conformal mapping theory of complex variable function and the principle of groundwater hydraulics,the analytical formula of seepage field of deep-buried water-rich circular tunnel under the condition of permeability anisotropy is derived.Taking the waterproof and drainage form of ’ water plugging and drainage restriction ’ as the research object,the influence of main permeability coefficient ratio,grouting circle parameters and initial support parameters on the seepage field of the tunnel is analyzed.(2)By the Monte-Carlo stochastic simulation technique,a two-dimensional stochastic fracture network is established.By solving the permeability tensor,permeability ellipse and the representative element volume(REV)of the stochastic fracture network,the applicable conditions of considering the fractured surrounding rock as an equivalent continuous medium seepage model are analyzed.(3)By establishing the numerical model of equivalent continuous medium seepage,the influence of permeability anisotropy of surrounding rock on seepage field of tunnel and stratum is studied under two conditions of main permeability coefficient direction and ratio of main permeability coefficient.Combined with equivalent lining parameters,the sensitivity analysis of orthogonal test was carried out,and the influence of surrounding rock permeability anisotropy and lining parameters on tunnel seepage field was studied from range analysis and variance analysis.