Study On Large Scale Shaking Table Test Method Of Shield Tunnel Under Non-uniform Excitation

Shaking table test is one of the effective measures to study the seismic response of structures at the present time.For underground structures such as tunnels,shaking table test is mostly carried out with the help of model box.The dynamic characteristics and boundary effects of the model box determine the accuracy of the test results.Although many scholars have made improvements on the model box,the boundary effect problem of a model box has not been well solved,and the test based on the model box needs to fill a large amount of soil in the test process,which increases the load of the shaking table and limits the size of the model tunnel.It is difficult to study the longitudinal response of large-scale shield tunnel on the shaking table test,and it is difficult to strictly conform to the similarity between the model soil and the undisturbed soil.At present,in the tunnel shaking table test based on model box,the test similarity ratio often designs the model structure and model soil separately,and the geometric similarity ratio of tunnel structure is mostly less than 1:25.Considering the difficulties,based on the principle of response displacement method,this paper proposes a loading device suitable for large-scale shaking table test of shield tunnel passing through non-uniform stratum.It is able to carry out the large-scale shaking table test of the shield tunnel to study the longitudinal seismic response of the tunnel passing through the abrupt soil stratum.The main contents of this paper are as follows:(1)The similarity ratio of tunnel model is obtained.The model similarity design method and joint similarity design method are introduced by the similarity theory.Based on the second similarity theorem and combined with dimensional analysis method,the similarity relationship of the shield tunnel shaking table test model with geometric similarity ratio of 1:12 is deduced,and the similarity constants of various physical quantities are obtained.According to the stiffness similarity ratio,the design stiffness of model joint is obtained.Based on the similarity relationship of test model designed,preliminarily determine the model materials that meet the test similarity ratio.(2)The analysis length of shield tunnel structure model is studied.Based on the longitudinal beam spring model,two shield tunnels with different analysis lengths of 200 m and1000m are calculated and analyzed.The comparison results show that when studying the seismic response of the shield tunnel for soil mutation,the analysis length of the shield tunnel can be intercepted from 100 m along both ends of the soil mutation section.The analysis length value can provide a reference for the analysis length value of the model test.(3)The feasibility of input mode of traveling wave effect in shaking table test of shield tunnel is studied.In homogeneous soil,the seismic response results with and without traveling wave effect are quite different,so it is necessary to consider traveling wave effect;In the shaking table test,the input of traveling wave can only be realized by setting the time difference between the arrays,that is,the influence of traveling wave can only be considered on the concerned section,while each point in the same array cannot simulate the traveling wave effect,so the result value on the same array is smaller than the actual value.In homogeneous soil,considering the time difference in the traveling wave input of the shaking table,if it is set as the time when the traveling wave passes through the center distance between the two arrays,the result will be too conservative.When the time difference is considered to be consistent with the time difference of the actual traveling wave,the seismic response at the key section is similar to the actual result.In the case of sudden change of soil,the influence of traveling wave will be eliminated by the influence of soil difference.In this case,considering the traveling wave effect has little impact.(4)The design scheme and detailed dimensions of the loading device for shaking table test are studied,and the finite element model of the test support is established by ABAQUS.The basic dynamic characteristics of the test support are obtained through modal analysis.(5)The feasibility of using the shaking table test loading device to analyze the seismic response of large-scale shaking table of shield tunnel crossing non-uniform stratum is analyzed.Based on the finite element model of the multi segment shaking table test support,the shield tunnel model and spring connection is established to form the finite element model of the shaking table test loading device-tunnel system,and the horizontal transverse action is input at the bottom of the test support to simulate the excitation process of the actual shaking table test,so as to study whether the loading device of shaking table test is applicable.The numerical simulation results show that the strength and deformation of the test support in the shaking table test loading device meet the requirements of "large load and small deformation",can better realize the input loading,and the regular pattern of the shield tunnel dynamic response are consistent with the reality.