Experimental Study on the Impact of the Starting of Shield Tunnels in Contact Channel Construction on Existing Shield Tunnels

The impact of shield tunneling machine starting on the deformation of the existing shield tunnel under load during the construction process of the shield tunneling method connecting passage is currently unclear. By designing a 1:10 scaled model experiment, conducted experimental research on the impact of shield tunneling machine initiation on existing shield tunnels. The experimental results indicate that, during the construction of the shield tunneling method connecting passage, under the action of the shield tunneling machine's top pushing reaction force, the existing shield tunnel at the starting end undergoes horizontal elliptical deformation within a range of about 1 tunnel diameter at the connecting passage position, while vertical elliptical deformation occurs at both ends. When a shield tunnel undergoes cross-sectional deformation, the horizontal diameter deformation is about 3-4 times that of the vertical diameter deformation. Horizontal bending deformation occurred in the direction of upward pushing reaction force within a range of approximately 1 tunnel diameter at the location of the connecting passage, and horizontal bending phenomenon occurred on both sides of it. The trend of vertical deflection deformation is the same as that of horizontal deflection deformation, and the amplitude is smaller than that of horizontal deflection deformation. The increase in horizontal diameter within the range of about 1 times the tunnel diameter at the location of the connecting passage leads to an increase in horizontal soil pressure on both sides of the tunnel, while the decrease in vertical diameter leads to a decrease in vertical soil pressure on both the top and bottom of the tunnel. The variation of soil pressure around the shield tunnel is the result of the combined action of cross-sectional deformation and longitudinal deflection deformation of the shield tunnel. It is recommended to consider both cross-sectional deformation and longitudinal deflection deformation in the stress analysis process of the shield tunnel.