| In shallow shield tunnels located in saturated soft soil,the long-term leakage of segment lining will have an important impact on the mechanical state of tunnels and surrounding strata during operation.Due to the structural characteristics of shield tunnels,with the increase of operation time,groundwater seepage will gradually occur at segment joints,bolt holes,grouting holes and other locations,resulting in a steady seepage field in the soil after a long time.The leakage of segments makes the lining become a local drainage boundary.The change of permeability will affect the distribution of seepage field around the tunnel,and then change the stress and displacement field in the stratum,and ultimately affect the overall consolidation settlement of the stratum where the tunnel is located with the increase of time.Aiming at shallow-buried shield tunnels in saturated strata during operation period,this paper introduces the boundary condition of local leakage water of lining.Based on the conformal transformation method of complex variable function,Airy stress function method of elasticity mechanics and Davis's non-linear consolidation theory,the calculation methods of seepage field,stress-displacement field and theoretical prediction methods of long-term consolidation settlement of strata around the tunnel under the condition of long-term leakage water of lining are studied.At the same time,the influence of the leakage degree of lining on the long-term mechanical properties of soil around the tunnel is analyzed,and the theoretical calculation value is compared with the numerical simulation value and the engineering measured value.The main research contents and achievements are as follows:(1)In continuous media,the analytical expressions of pore water pressure,total head and seepage flow around shallow-buried tunnel under steady seepage flow are obtained by using the method of calculating soil,grouting layer and lining,according to the boundary conditions of pore pressure and seepage flow at the inner edge and surface of tunnel and the continuous conditions of seepage flow.The influence of relative permeability of lining,grouting layer and soil on the distribution of groundwater seepage field is analyzed.The evaluation index of lining leakage is defined.According to the index value,lining is divided into different leakage boundaries,and the actual leakage state of tunnel is judged based on it.(2)Based on Airy stress function method of elasticity mechanics,on the basis of theoretical analysis of steady seepage field in the first part,the formulas for calculating stress and displacement fields of soil around tunnel considering the influence of lining seepage are derived,and the influence of groundwater seepage on the size and distribution of stress and displacement fields in soil is further analyzed.The calculation program of MATLAB is compiled,and the distribution law of stress and displacement of surrounding rock under different local seepage conditions is obtained.(3)Based on Davis's non-linear consolidation theory,the local seepage boundary condition of lining is introduced.The analytical solution of long-term consolidation settlement of stratum considering the non-linear change of permeability and compressibility of soil with time is derived by taking the calculation results of seepage field and stress field of soil as initial boundary conditions in the first and second parts of this paper.Stepwise search method and time discrete method are used in the solution.A step-by-step iterative algorithm is designed for the calculation of non-linear consolidation.The calculation process is realized by MATLAB programming.By comparing the theoretical predicted value with the measured value,the reliability of the calculation formula is verified.In addition,the influence of dinfferent seepage conditions of lining on the average consolidation degree of soil around the tunnel,the dissipation time of excess pore water pressure,the subsidence rate of stratum and the surface subsidence curve are analyzed. |
PDF Full Text Request