Optimal Analysis On Excavation Method Of The Chongqing Rail Transit Line Four Xiazibian Station

With the acceleration of the city process,the construction of the subway is also steadily advancing,the construction of large section tunnel is becoming more and more common.The excavation of large section tunnel is easy to lead to the vault settlement and the convergence value is too large,the impact on the surrounding buildings is also significant.Therefore,the selection of construction technology of large section tunnel has great effect on the deformation of surrounding rock.It is an important task of tunnel engineering to choose a construction technology which can meet the requirements of safety and economy and meet the deformation demand of the surrounding environment.In this paper,based on the Chongqing Rail Transit Line Four a station project,the finite element software ANSYS is used to establish a model to simulate the deformation and stress changes of surrounding rock and support structure during construction.Through comparison,choose the construction method that suitable for this project to achieve the purpose of optimization.Though the study of this paper,several conclusions are drawn as follow:(1)This paper introduces the advantages and disadvantages of the CRD method,the double side drift method,the big arch feet method and the hole pile method,and also introduce the construction process and construction points of the four methods.(2)Through the finite element software ANSYS to simulate the excavation of the double side drift method of a station,the calculated values for the final settlement of vault is 11.3mm,the maximum horizontal displacement is 20.8mm,the maximum value of the first principal stress in surrounding rock is 2.62 MPa,the minimum value of the third principal stress is-2.92 MPa,the maximum value of the first principal stress in lining is 11.2MPa,the minimum value of the third principal stress is-8.6MPa;(3)Through the finite element software ANSYS to simulate the excavation of the big arch feet method of a station,the calculated values for the final settlement of vault is18.9mm,the maximum horizontal displacement is 6.8mm,the maximum value of the first principal stress in surrounding rock is 2.41 MPa,the minimum value of the third principal stress is-4.81 MPa,the maximum value of the first principal stress in lining is10.2MPa,the minimum value of the third principal stress is-7.76MPa;(4)Through the finite element software ANSYS to simulate the excavation of the hole pile method of a station,the calculated values for the final settlement of vault is11.8mm,the maximum horizontal displacement is 5.3mm,the maximum value of the first principal stress in surrounding rock is 0.67 MPa,the minimum value of the third principal stress is-1.55 MPa,the maximum value of the first principal stress in lining is3.11 MPa,the minimum value of the third principal stress is-3.90MPa;(5)TO compare these calculation results,we recommend use the double sidemethod to construct this metro tunnel;(6)Through the comparison of monitoring measurement and finite element calculation of a station,the trend of the changes is consistent,so the finite element method can be used to guide the tunnel construction.