Study On Influence Mechanism Of Sewage Pipeline Leakage On Subway Tunnel Structure And Surrounding Strata

In recent years,the pace of urbanization construction has been speeding up.In the process of development and utilization of urban underground space,underground pipeline,especially sewage pipeline,is vulnerable to construction disturbance to appear damaged or broken,so as to cause long-term leakage disease,which causes the pavement collapse and has an adverse effect on the structure of subway tunnel below.Based on the background of deep underground water level and the existence of subway tunnel in a city,this paper analyzes the influence of long-term leakage of underground sewage pipe on surrounding stratum and tunnel structure below based on the methods of literature investigation,numerical simulation and model test.The main research work and results are as follows:(1)Eight working conditions were designed according to different formation conditions,pipeline burial depth,water pressure in the pipe and seepage point location,and the influence of each factor on the diffusion range of pipeline seepage and the morphological change of the leakage area was studied by numerical simulation method.The results show that: 1)in the tunnel-free stratum,the development of pipeline leakage zone roughly goes through three stages: "heart-shaped,round-shaped and elliptic".When the tunnel is located under the pipeline,it changes the seepage path of water,and the leakage zone is approximately "pear-shaped" in the later period.2)The greater the buried depth of the pipeline,the longer it will take for the seepage water to spread to the ground.When the buried depth reaches a certain depth,the leakage area will not be able to reach the surface.3)With the increase of water pressure in the pipe,the diffusion rate of seepage water leakage increases,and the proportion of the high saturation area occupying the whole leakage area increases obviously,and its shape is closer to the overall shape of the leakage area;4)The location of different pipe seepage points mainly affects the water diffusion form in the early stage of leakage,but has relatively little influence on the scope of the late seepage area.(2)Based on the finite element software ABAQUS,the fluid-solid coupling analysis was carried out on the leakage process of sewage pipe when the centreline of pipe and tunnel coincides,and the change law of stratum deformation and tunnel structure stress during the leakage process was studied.The results show that: 1)At the initial stage of leakage,the range of ground subsidence and its settlement value are relatively small,and gradually increase with the expansion of the leakage area.The overall settlement trough at different times presents an approximate symmetrical "unimodal" shape.The maximum settlement point is located on the surface directly above the pipeline,and the settlement value at other locations decreases with the increase of the horizontal distance from the pipeline.2)The stress of the tunnel lining structure will change with the leakage,the maximum position of the bending moment and axial force are located in the vault and the arch,and the internal force values in the leakage process show a trend of "first increase,then decrease and then tend to be stable".When the seepage water seepage to about 1 times the diameter of the tunnel arch bottom,the internal force reaches the peak,and the safety factor of the vault and the arch bottom is the minimum.(3)By carrying out three sets of indoor model tests of pipeline leakage under different working conditions,the influence of the relative position of the pipe-tunnel on the variation rule of formation deformation and tunnel structure stress in the leakage process was studied,and the results were compared and verified with the numerical simulation results.The results show that: 1)With the increase of the horizontal distance between the pipe and tunnel,the time required for water leakage to reach the tunnel location increases,and the formation wetting range far away from the pipeline side decreases.However,the maximum height and width of the leakage zone under different working conditions at the same time have little difference,and the overall development law accords with the numerical simulation results.2)The surface settlement curves in different pipe-tunnel conditions are roughly symmetrical around the pipeline center line,and the settlement near the ground directly above the pipeline is the largest,and the difference between the maximum settlement values in different conditions is small.3)When the pipeline deviates to the right,the approximate bias of the tunnel will be generated in the leakage process,which changes the overall stress distribution of the lining structure.The maximum position of the bending moment and axial force and the position of the most unfavorable section of the structure will also be deflected at different angles.The overall law obtained by the two research methods is basically the same.