Study On Construction Reinforcement Measures For Diversion Tunnel Adjacent To Railway Tunnel

As the scale of tunnel construction continues to increase,it is always inevitable to construct new tunnels near the existing tunnels.The construction of a new tunnel will redistribute the surrounding rock stress field again,which will worsen the stress state of the existing tunnel.This will have a very negative impact on the existing tunnels.Therefore,research on this type of project is of great significance.This article is based on the North Main Canal Project of Xiangjiaba Irrigation District.Fast Lagrangian Analysis of Continua is used: Conduct research on the impacts of existing tunnels,such as deformation,changes in lining internal forces during the construction and operation of the upper-crossing diversion tunnel at different distances from it.Then further study is the reinforcement measures and optimization during the construction of the diversion tunnel.Some conclusions of the study are mainly listed below:(1)During the construction of the overpass of the diversion tunnel,the overall deformation trend of the existing tunnel is "vertical extension and lateral compression".In the normal operation of the diversion tunnel,when the hydraulic load increases,the existing tunnel has a deformation tendency of "vertical compression and lateral extension".The deformation trend of the existing tunnel is always the largest at the point orthogonal to the newly built tunnel,and the horizontal convergence deformation of the arch waist is greater than the arch toe,and the vertical displacement of the vault is greater than the invert.(2)Before and after the completion of the construction of the diversion tunnel,the internal force distribution law of the existing tunnel lining remained basically unchanged,but it decreased to varying degrees.During the normal operation of the diversion tunnel,as the hydraulic load increases,the internal force value of the existing tunnel lining increases to varying degrees.But the distribution law remains basically unchanged.The maximum axial force value change is always significantly greater than the maximum bending moment value change.As the spacing increases,the impact of the construction and operation of the diversion tunnel on the existing railway tunnel becomes less and less.(3)During the construction of the diversion tunnel overpass over the existing tunnel,the displacement trend of the diversion tunnel circumference is "vertical compression,lateral compression" The roof subsidence is almost unaffected by the existing tunnels.The uplift of the tunnel bottom and the horizontal convergence of the tunnel waist are the smallest at the orthogonal points of the two tunnels,and gradually increase within 15 m along the axis direction and then stabilize.(4)When taking reinforcement measures,as the depth of the pile foundation increases,its ability to control the horizontal convergent deformation of the existing tunnel and the change of the internal force of the lining is stronger.When the pile depth is 5m,the reinforcement effect is relatively poor.The pile depth of 10 m and 20 m have good reinforcement effects and the difference is small.It is recommended that the depth of the pile foundation be 10 m,and the distance from the outer side of the second lining of the existing tunnel is 2m.(5)Both the original reinforcement measures and the optimized reinforcement measures can effectively reduce the impact of the overhead tunnel construction on the existing tunnel.The two effects are equivalent,and the optimized reinforcement measures can reduce the workload by nearly half,and greatly shorten the construction period on the basis of ensuring the effectiveness of the reinforcement measures.