Abstract: The safe shield overcrossing adjacent existing operation tunnel during launching should be guaranteed. Hence, the key and difficult points of the project are analyzed, the construction control measures for shield overcrossing are introduced, the overcrossing effect is analyzed according to the control of construction parameters, and the deformation law of existing tunnel is analyzed. The analytical results show that: (1) The successful shield launching according to design can be effectively ensured by adjusting the launching base to be consistent with the slope of shield tunnel axis and welding the guide rail at the steel ring of the portal. (2) By injecting lubrication material, clay shock slurry, to the shield, the thrust force can be reduced, and further the disturbance to the existing tunnel can be reduced as well. (3) The existing tunnel displaces towards upside and tunneling direction before shield cutterhead crosses; after the gravity center of the shield overpasses the existing tunnel, the vertical deformation of the existing tunnel reduces and becomes stable after the shield tail passes; the deformation of the existing tunnel towards tunneling direction increases sharply when cutterhead is right above the tunnel, and becomes stable after the shield tail passes.

Key words: shield launching, overcrossing existing tunnel, clay shock slurry, shield attitude control, tunnel reinforcement, field monitoring