Study On Construction Method Of Foling Tunnel Portal Section Under Shallow And Weak Surrounding Rock

Much entrance of highway tunnel is strong weathering zone,where the rock is generally broken,and usually have layers folder,covering more general thin layer.Under the construction,how to make rational use of good variety of construction methods,reduce engineering investment,improve efficiency,and at the same time to strengthen the mechanism of formation damage,a variety of support methods and the interaction between the rock of the study,which is need to be addressed urgently.This paper introduces a variety of support and excavation methods in the entrance of mountain tunnel,summed up the characteristics of these methods and the application of stratigraphy,as well as the mechanism of these methods and construction techniques, and compared the advantages and disadvantages.Under the construction of Foling tunnel in Anhui Province,bench reservation core soil,with the use of common international procedures for the finite element method-ANSYS finite element model to establish the basis of the actual terrain model,bench reservation core soil,CD method, CRD method,and twin-side heading method are adopted based on FLAC^3D to study on suitable method and stability principium of entrance of long and large tunnel in poor stability and complex geological conditions,combined with the settlement of crown, plastic zone distribution and development in special section of tunnel.Considering the construction cost,the simulation results show that the twin-side heading method is the optimal act.For twin-side heading method mediated process characterized by complexity,a reasonable implementation plan is designed,and the key technology of the construction is researched.Finally,This paper introduces the causes of collapse incidents in the entrance of Foling tunnel,and bring forward the appropriate and reasonable measures.The conclusions of this paper,provide a technical basis for guidance in the excavation of Foling tunnel,so it could scientifically guide the dynamic construction of long and large tunnel and ensure safety for similar construction practice.