The Influence And Safety Analysis On Existing Rail Caused By Shield Tunneling Pass Through Underpass

With the large-scale construction of underground transportation in China,the construction condition of urban shield tunnel is increasingly complicated.It is inevitable to encounter the situation of shield tunneling through railway underpass,which seriously affects railway safety operation due to the deformation of rail.This paper based on the actual project—Zhengzhou metro Line 5 go through underpass,carries out the research from three aspects of model test,theoretical analysis and numerical simulation.The main research work of this paper is as follows:(1)Model tests are conducted,the experimental results were compared with the theoretical values,and then the traditional empirical formula was modified and verified by finite element method.The results show that the modified empirical solution can better fit the deformation of rail.(2)According to the tunnel pass through railway underpass model test,the rail settlement is analyzed by the improved "two-stage" method.The "soil-structure separation model" was added to the previous Winkler elastic foundation model to obtain the theoretical deformation solution of rail in this condition.Finally,the theoretical calculation results were compared with the model test results.The results show that the "gap" between the underpass and the bottom soil will affect the deformation of the rail,and the improved "two-stage" method is more accurate to calculate the deformation of the upper rail.(3)Based on the actual project,a finite element calculation model is established to study the influence of shield construction process on the surface and railway underpass.By comparing the finite element results with the measured data,it is found that the underpass attitude changed when the shield machine was passing through it.And the underpass presents a trend of overall subsidence with the shield machine coming out from underneath it.The deformation of the upper rail is relatively large and becomes stable as the shield drives away from the underpass area.(4)The influence of shield construction environment and construction parameters on underpass and rail deformation is studied.Through comparing numerical simulation results,it is found that the closer the tunnel central axis is to the central axis of railway underpass,the less the influence of shield construction on railway rail and underpass.The deformation of the upper railway and underpass increases with the increase of tunnel diameter.The settlement of railway track and underpass will decrease with the increase of soil cohesion and internal friction angle.Among the construction control parameters,the loss rate has the greatest impact on the upper structure,followed by the grouting pressure,and the excavation surface pressure has a relatively small influence.This paper has practical reference value for calculation and safety analysis of railway rail deformation caused by tunnel pass through underpass.