Influence Analysis of Setting Separation Piles for Metro Shield Tunnel Sidecrossing Highspeed Railway Bridge Pile Groups

Taking the case of certain shield tunnel side-crossing high-speed railway bridge pile group foundation as an example, the influence of shield tunnel side-crossing construction on high-speed railway bridge pile groups is studied. By taking separation piles measure to reduce the impact on pile groups, different scopes, locations, and depths of separation piles are analyzed and compared. Following conclusions are obtained: 1) When there is an angle between tunnel axis and the foundation of pile groups, uneven settlement will take place in pile foundation and bearing platform. The deformation of pile groups is affected by the platform rigidity. The position of piles and the platform near the tunnel are generally settlement deformation, and the deformation increases with the distance decreasing. Affected by platform rigidity and group piles effects, the partial position on the far side to the tunnel are upward deformation. Extra attention should be spared on the uneven deformation. 2) The maximum deformation position of piles is located above the shield tunnel bottom. The value of piles deformation below the shield tunnel bottom is small. Therefore, the measure of soil improvement is mainly for the upper piles above the bottom of tunnel. 3) Adopting separation piles measure can reduce the deformation by up to 40%. The separation piles play an important protection role. 4) The optimal scope of separation piles is 1.0 D~1.5 D (D is the shield tunnel diameter) outside the projection of pile groups. Separation piles are less useful when the scope excesses 1.5 D. 5) Considering using separation piles to decrease the deformation of existing bridge piles, it should be designed as close as possible to the tunnel, so that the impact of the tunnel, as well as that of the construction of separation piles, to the existing high-speed railway bridge foundation will be smaller. 6) It is most effective and most economical to design the separation piles 1~3 m below the tunnel bottom and set up according to demand.