| With the continuous improvement and expansion of China's railway,highway and railway networks,in the prosperous areas of the city or in some special sections,the construction of new tunnels and existing structures is not uncommon,and the forms encountered are more and more complicated.Underground engineering is sensitive to proximity construction.The process of new tunnels crossing existing structures has great influence on each other and may even cause damage to existing structures.The cross-tunnel is a kind of adjacent tunnel.The cross-section of the tunnel is often a critical part of the project.The force structure of the cross-section is complex and has a great influence on each other.The selection of excavation methods,reinforcement of rock and soil and construction monitoring There are special requirements in other aspects.Repeated excavation disturbances lead to an increase in surface settlement,and the excavation disturbance of the subsequent tunnel will also affect the structural safety of the preceding tunnel.Due to historical reasons,Chongqing has retained a large number of civil air defense works,which are intensive and complicated,which has brought certain difficulties to the construction of underground transportation in Chongqing.Based on the actual project,this paper studies the deformation and stress laws of new tunnels and existing man-made defense projects in the near-construction process,and uses FLAC3 D software to numerically simulate and optimize the two construction schemes.The specific research contents are as follows:(1)In view of the adverse effects of tunnel construction on existing structures in the neighborhood and nearby areas,the neighborhood catastrophic changes in tunnel construction were studied,and the deformation,catastrophic mechanism,basic characteristics and influencing factors of tunnel construction neighborhood were expounded.The research on the tunnel construction affected area mainly focuses on the estimation of the area affected by the tunnel construction and the division of the regional influence degree.According to the current technical norms and standards in China,two methods for estimating and dividing the influence domain are introduced,and the existing tunnel control standards and the division of the proximity of the three-dimensional cross tunnel are discussed.(2)Summarize the application of numerical analysis in tunnel engineering,elaborates the finite difference method and the calculation idea of FLAC3 D,and introduces the most commonly used yield criterion for geotechnical materials in numerical analysis,namely Drucker-Prager and Mohr-Coulomb yield criterion;To ensure the accuracy and rationality of the numerical model,the simulation of the construction of the new Austrian tunnel is studied,including the construction sequence,lining stress and load distribution mode and construction defects.The flow of numerical simulation of the tunnel is introduced.The value of the support is described based on FLAC3 D.Simulation method and numerical simulation method for tunnel excavation.(3)For the intersection of the tunnel and the existing man-made defense project,two tunnel excavation schemes were simulated,that is,the excavation of the civil anti-cavity chamber without backfilling and the backfilling of the civil defense cavern with slurry masonry and then excavation.According to the geological survey data and design documents,the three-dimensional model is established and the calculation parameters are selected.The numerical simulation of the double-track tunnel excavation is carried out and relevant data are obtained.The deformation of the surrounding rock of the tunnel,the initial lining displacement,the axial force of the anchor,and the deformation of the support structure of the civil air defense tunnel In the aspect of surface settlement,the law of tunnel construction is studied.On the basis of numerical analysis,the selection of excavation scheme for tunnel crossing civil air defense cavern is carried out. |
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