Model Test And Numerical Simulation Analysis Of The Influence Of Pipeline Leakage On Subway Shield Construction

In recent years,accidents caused by pipeline leakage have been reported in the subway shield construction.The reasons are mainly as follows,the subway shield construction inevitably lead to the formation of the disturbance,causing deformation and even destruction of the water supply and drainage pipe in the soil,the pipeline seeps into the soil,and weakening the mechanical properties of soil layers.Construction disturbance increases formation deformation settlement and pipeline leakage,the formation collapse under the joint action of pipeline leakage and formation deformation and settlement.With the research background of hefei subway construction,the typical sandy soil in hefei area is the experimental material,Research on the influence of pipeline leakage on subway shield construction by means of indoor model test and numerical simulation.Two phase analysis methods are used to study.In the first stage,the influence of leakage on surface subsidence,pipeline settlement and tunnel pressure change is studied by using the indoor model test method.In the second stage,numerical simulation method is adopted to study the deformation law of surface subsidence in subway construction and the distribution law of seepage field in the surrounding strata under the condition of pipeline leakage,and compared with indoor model test results,analysis the influence law of pipeline leakage of subway construction.The main results are as follows:(1)In the test where no leakage occurred in the pipeline,the surface settlement caused by the tunnel excavation resulted in the formation of a "single-peak" sedimentation tank with an approximately normal distribution.Due to the pipe-soil interaction,the pipeline settlement curve also approximates a normal distribution.The maximum settlement occurs directly above the excavation tunnel,and the settlement value decreases with the distance from the tunnel centerline.(2)In the case of different seepage stages,the influence of leakage on pipeline and surface subsidence d as the time of seepage during tunnel excavation goes backwards.In the case of leakage pressure and leakage location and the relative position of the excavation tunnel,the scope of the leakage is basically unchanged.It is limited to the range of 50 cm from the center line of the tunnel,and the settlement value of the measurement points away from the excavation and seepage position is almost unchanged.The earlier the leakage of the pipeline,the greater the immediate impact on the sedimentation of the stratum.In the absence of formation instability and failure,the settlement amount due to seepage is about 35% ~ 38% of the final settlement.(3)Because of the influence of the tube-soil interaction,the ground settlement caused by pipeline leakage value increases,pipeline settlement also will increase,but relative to the surface subsidence,pipeline settlement decreases slightly.The sedimentation of sand soil and the final stability curve indicate that the settlement of the pipeline is similar to that of a simple supported beam with a uniformly distributed load on both ends.(4)During the tunnel excavation,the top of the tunnel segment is always subjected to the pressure of the upper soil and gradually increases.In the pipeline leakage stage,the surface settlement caused by the leakage of water increases,and the stress on the top of the tunnel segment increases significantly;after the leakage is completed,the stress gradually stabilizes as the surface settlement value no longer changes.(5)In the case where the relative position of the pipe-tunnel is constant,the growth rate of the impact range of the pipeline seepage water increases slowly until it does not change with the start time of the leakage.The surface settlement data obtained by the simulation is strictly in line with the centerline of the tunnel,and the settlement curve caused by pipeline leakage and tunnel excavation is normally distributed.In the condition of the relative position of the pipe-tunnel and the pressure head,the final settlements produced at different leakage periods are close to each other.When seepage water is produced in the pipeline,the settlement of the surface at this time is much larger than the amount of the pipeline that has not leaked.