INFLUENCE OF LARGE-SECTION RECTANGULAR PIPE JACKING ON DEFORMATION OF EXISTING SUBWAY TUNNELS

During the construction of a large section rectangular pipe jacking over an existing subway tunnel,the unloading effect caused by the close excavation of the soil leads to the floating deformation of the existing subway tunnel,which can endanger the safety of subway operation. In order to study the influence of the large-section rectangular pipe jacking construction on the deformation of existing subway tunnels,this paper takes the rectangular pipe jacking project of the comprehensive pipe corridor in Changhe West Road(Zhaoshan Street~Luyang Street),Tongzhou District,Beijing as research project. This paper uses FLAC^3D finite difference software,establishes a 3D numerical model of a large section rectangular pipe jacking over an existing subway tunnel and studies the floating deformation pattern of the subway tunnel caused by double-line rectangular pipe jacking construction and the influence of different anti-floating weights on the deformation of the existing subway tunnel. The simulation results are compared with on-site monitoring data to verify the accuracy of the numerical model. The results show that the floating deformation of the subway tunnel caused by the double-line pipe jacking construction is larger than that caused by the single-line pipe jacking. The maximum floating deformation is located at the axis of the pipe jacking tunnel. When a counterweight similar to the weight of the soil lost by excavation is applied,the original horizontal deformation pattern of the subway tunnel can be changed as follows. (1)The subway tunnel that has been traversed first moves to the direction of the originating shaft; (2)The subway tunnel that has been traversed later moves to the direction of the receiving shaft. Floating deformation and tensile stress of subway tunnel decrease with the increase of anti-floating weights. Applying anti-floating weight of 50% of the lost soil weight during excavation can control the floating deformation of the subway tunnel within 1.4 mm. The results provide a reference for the anti-floating design of the subway tunnel in this project.