Study On Interaction Mechanism Between Undercrossing Shield At Short Range And Existing Subway Tunnel

With the increasing of metro rail construction in main cities, there are more and more crossing tunnel construction. In the undercrossing project, the construction of new shield tunnel will have a great influence on the existing subway tunnel. Thus, the interaction mechanism of the undercrossing shield, existing subway tunnel and surrounding strata has practical significance in the crossing construction.The project of Shenzhen new Metro Line 9 shield tunnel undercrossing the existing Metro Line 4 tunnel is applied in the research. Based on the monitoring data of the surface and existing subway tunnel in the project, the interaction mechanism between the undercrossing shield tunnel and the existing subway tunnel is studied. In addition, the deformation law of the existing subway tunnel, surrounding strata and the surface is taken into account by means of theoretical analysis, 3D numerical calculation and data fitting.Considering the timeliness, the whole process of shield tunnel undercrossing is divided into phases. Researches show that during the period from the arrival of the shield machine cutter to the shield tail completely out of the existing subway tunnel, the settlement deformation of existing subway tunnel, surface and strata have a fastest rate and a maximum amplitude. In this period of time, the settlement accounts for 60%~80%. Based on Peck formula and the theory of beam on elastic foundation, the simplified calculation formula of the existing subway tunnel structure longitudinal deformation is deduced as well as the deformation of same depth stratum caused by the construction of the undercrossing shield. Combined with the field measured data, the foundation modulus is analyzed, the results show that the foundation modulus reduces about 32.75% in the process of shield tunnel undercrossing. According to the field monitoring data and the finite element numerical simulation, the influence of the existing subway tunnel on the settlement deformation of above strata and surface is analyzed. The actual effect of grouting reinforcement measures behind the concrete segments is also studied, which is taken to control settlement deformation of the existing subway tunnel. Studies show that the existence of the subway tunnel make upper strata and surface settlement deformation decreases about 50% compared with the conventional construction of shield tunnel excavation. Grouting reinforcement measures behind the concrete segments can directly change the deformation trend of existing subway tunnel structure and cause the deformation of tunnel structure with a certain raise. Thereby it can effectively control the settlement deformation of the existing metro tunnel structure.