| From the end of the 20 th century to the present,with the accelerating pace of urbanization in China,the rapid growth of population density in urban areas and the increasing demand for electricity,the electricity transmission mode has changed from the initial overground transmission to underground power tunnel transmission.For some developed cities,the supporting facilities of underground rail transit are relatively perfect,and the power tunnel will inevitably cross the existing subway lines in the construction process.However,due to the change of the initial stress field,the existing subway tunnel will produce additional internal force and additional displacement,which may lead to cracking and water seepage of the existing subway tunnel segment,which seriously threatens the safety of the tunnel operation.Therefore,it is of great significance to study the disturbance mechanism of power shield tunnel orthogonal underpassing existing metro tunnel construction.In this paper,based on the power tunnel project of Guangzhou Nanda trunk line,field investigation,centrifugal model test and numerical analysis are adopted to study the construction disturbance mechanism of the power shield tunnel’s orthogonal underpassing of the existing subway tunnel.The main results are as follows:1.The grating optical fiber sensing technology was introduced into the geotechnical centrifugal model test system of Chang ’an University,and the tunnel centrifugal model test system based on FBG sensing technology was established,which greatly reduced the error of test results caused by a large number of endings and wiring in previous tests;2.Based on the FBG fiber grating tunnel centrifugal model test system,centrifugal tests were carried out to study the disturbance mechanism of power shield tunnel orthogonal underpassing existing subway tunnel construction with ground loss rate and net distance as two main influencing factors.Centrifugal tests show that with the increase of ground loss rate and the decrease of net distance,the maximum settlement value of ground surface and existing tunnel vault as well as the maximum additional longitudinal bending moment,circum-axial bending moment and circum-axial force caused by deformation all increase,but the distribution of settlement and internal force does not change.The confining pressure does not decrease obviously at the vault,but at the bottom and waist of the arch.Under the influence of soil arching effect,the longitudinal confining pressure distribution along the existing tunnel and the soil pressure distribution in the interlayer presents a "V" shape distribution.When the local layer loss rate is less than 0.5%,and the net distance is less than 0.5DE,the soil arching formation is poor,and the increase of ground loss rate and net distance is more conducive to the formation of soil arching effect.The generated position is basically 6m away from the central symmetry plane of the existing tunnel.3.The three-dimensional finite element model under different working conditions is established.The calculation and analysis show that the existing tunnel structure not only produces vertical tensile and horizontal convergent deformation,but also has torsional deformation during the construction process of the new power tunnel.The settlement value at the bottom of the arch is greater than that at the vault,and the surface settlement at the axis of the existing tunnel is smaller than that on both sides of the axis,which indicates that the existing tunnel inhibits the upward development trend of the deformation of surrounding soil.;4.Numerical simulation results compared with centrifugal test analysis found that the two kinds of research methods in data exist certain differences,this basically is probably caused by the numerical simulation will be regarded as isotropic soil,but the results change both settlement and internal force of tunnel,and the centrifugal model experiment results show good consistency,and proves the test conclusion;... |
