Study On Seismic Responses Of Shield Tunnel In Soft Soil Foundation

As the most ideal way to solve the traffic congestion in the metropolis,the subway will have a particularly broad development space in the future urban construction.At present,the shield tunnel with its unique advantages have been widely used in many construction projects,more and more cities use shield tunneling method to build subway tunnels.All previous occurrence of strong earthquakes consistently showed that soft soil will increase the damage degree of earthquake.Therefore,it is very necessary to study the seismic dynamic response of subway shield tunnel combined with the soil condition in soft soil area.In this paper,taking a subway shield tunnel in soft soil area as the project background,large-scale general finite element software ABAQUS were mainly used to deep study the lateral earthquake dynamic response characteristic of the shield tunnel,which provides reliable basis for optimization design and simplified seismic calculation method of subway shield tunnel in soft soil area.The main contents and conclusions of this paper are as follows:1.Shaking table model test of shield tunnel in soft soil area was carried out with geometric similarity ratio of 1/30.The dynamic response characteristics of tunnels and the influence of tunnels on surrounding rock were analyzed,in order to provide a reliable basis for software analysis.2.Based on the definition of contact,the constitutive relation of soil,the selection of damping and the boundary conditions,a three dimensional finite element model of lining structure-soil-infinite element was established.Taking the tunnel stress and deformation under the action of tunnel gravity and soil gravity as the initial conditions,the multi-step analysis was used to analyze the dynamic response time-history of subway shield tunnel under the initial conditions.3.Comparing the strain data of the experiment and simulation,we can get the same consistent rule: the strains at the places with central angles of ±30° to the top or bottom of the tunnel structure are larger than other places.The simulation results are in good agreement with the experimental results,which verifies the rationality of the model.4.Through the analysis of the acceleration,displacement,stress and deformation response of the lining structure under different earthquake intensity and different seismic waves,it was found that the soft soil has obvious amplification effect on the acceleration of the earthquake;the existence of the tunnel has a reduced effect on the acceleration peak value of the surrounding soil;the circumferential stress of lining structure was obviously larger than the axial stress.5.According to the analysis of the structural seismic response characteristics,the seismic fortification measures were put forward to reduce the damage of the tunnel under earthquake action.