Study On The Influence Of Rock Foundation Pit Excavation On The Deformation Of Existing Tunnel

With the rapid development of a large number of urban underground rail transit system and underground complex pipeline corridor system at home and abroad,the threedimensional development of underground space is a trend of the future development of each city.The excavation of foundation pit has become an inevitable new situation in the above or adjacent underground tunnel.Due to the tensile strength of concrete is very small,too large lining deformation,will lead to cracks in the lining,coupled with the impact of groundwater seepage,the operation of the tunnel safety hazards.Based on the actual project,this paper carries out the analysis and calculation of the displacement of the tunnel under the rock foundation pit excavation.According to the monitoring results of tunnel lining deformation,the FLAC^3D numerical simulation software was used to analyze the deformation law of the existing tunnel lining under the super close distance rock foundation pit excavation.The main research work and production of the dissertation are as follows:（1）Through dynamic monitoring of the excavation of the tunnel vault,arch waist,the displacement of the bottom of the arch and the deformation of the lining crack,get the rock foundation pit unloading,lining displacement deformation law: Under the condition of rock mass,the vertical displacement and the horizontal convergence displacement of the arch and the arch are gradually changed with the excavation of the foundation pit;The greater the excavation depth,the greater the change of tunnel lining displacement;The nearer the center of foundation pit,the larger the tunnel displacement;Vertical displacement of arch crown is larger than vertical displacement,and there is a certain proportion of vertical displacement and horizontal convergence displacement;With the excavation of foundation pit,the vertical crack of lining becomes smaller and smaller,and the transverse crack is larger.（2）Using FLAC^3D software to simulate the actual excavation of foundation pit engineering,analysis of tunnel lining stress and displacement nephogram and stress curve of stress and displacement.In the process of rock foundation pit excavation,the law of displacement and stress distribution of tunnel lining are obtained;The stress Lode parameters μ_σ were used to judge the stress state of the inner and outerside of the arch vault and spandrel,the arch foot and the arch bottom.（3）Through the comparison of 3D simulation and measured data,the results of numerical simulation are consistent with the actual excavation results.Using numerical simulation method to analyze the influence of excavation on the existing tunnel is reasonable.（4）Investigate the influence of excavation width and length of excavation on the existing tunnel.Based on the calculation results,the formula of the maximum deformation of the tunnel under the different excavation width and length is fitted.The influence of foundation pit excavation on the deformation of existing tunnel lining under the condition of three kinds of rock strata（mudstone,sandstone and limestone）is simulated.Obtaine the deformation law of the existing tunnel under the excavation of foundation pit.（5）Two kinds of different excavation methods are simulated respectively in transverse and longitudinal blocks.From the displacement and stress Lode parameters to determine the different excavation methods,the law of structural displacement and stress variation.Determine the optimal excavation method.The optimized excavation scheme is applied to practical engineering.Compared with the monitoring data,it is found that the optimized scheme has smaller deformation and better stress state.