Study On Mechanical Response Of Cross-Overlap Tunnel Construction Based On Numerical Simulation Method

With the continuous development of urbanization,urban traffic becomes increasingly congested,so the utilization of urban underground space is paid more and more attention.The underground three-dimensional transportation projects are increasing day by day,because there are many surface buildings,existing underground buildings and dense surface people in urban underground space.Therefore,compared with the single tunnel project,the construction of underground three-dimensional transportation project is more difficult and faced with more problems.This thesis mainly relies on a new tunnel in a planning to pass through the existing tunnel project in short range orthogonal,and discusses the influence law of tunnel construction under the new tunnel on the displacement field,stress field and structural internal force of the upper tunnel,as well as the mechanical change law under different tunnel clear distance,supporting structure parameters,surrounding rock level and excavation method through the numerical simulation research method.The main research achievements and conclusions of this thesis are as follows:(1)This thesis systematically statistics the cases of cross-overlapping tunnels in China,obtains the deformation characteristics,construction methods,tunnel spacing and other information of each case,analyzes the existing cases of cross-overlapping tunnels in China under different stratum conditions and the deformation and distribution law of tunnel,as well as the relationship between tunnel spacing and the stratum where the tunnel is located and the construction method,and summarizes the influence law of cross-overlapping tunnel deformation.(2)The principle of the horizontal layer method is elaborated,and the conversion formula of the thickness of the layer under the single layer and the layer under the single layer method is derived according to the horizontal layer method.Combined with the formula of the horizontal layer method and Sagaseta mirror method,the calculation model of the interaction between the "lower tunnel--upper tunnel--the overlying soil layer" is established respectively when the single layer and the multi-layer soil are covered.The displacement and deformation problem of cross-overlapping tunnel is transformed into a homogeneous soil deformation problem,and the formula for calculating the displacement of new tunnel soil layer is derived when the existing tunnel exists.(3)FLAC3D numerical simulation software is used to simulate the construction process of the lower tunnel passing through the upper tunnel in a short distance.Study the displacement and mechanical change law of the upper tunnel during the construction of the lower tunnel.The change law of displacement,axial force and bending moment increment at different sections of upper tunnel along its longitudinal length is discussed.(4)By using FLAC3 D software,the three-dimensional numerical model of the underpass tunnel is established,and the influencing factors of the cross-overlapping tunnel are analyzed.From the Angle of displacement,structural internal force and surrounding rock stress,the influence law of the lower tunnel construction on the upper tunnel under different influencing factors is studied.The influence laws of different tunnel spacing,different supporting structure parameters(elastic modulus of lining,thickness of lining,),different surrounding rock levels and different excavation methods on the construction mechanics and stability of the upper tunnel are obtained.According to the results of numerical simulation,the expression of criterion based on tunnel spacing is proposed,which can provide some help for the construction and design of underpass tunnel.