盾构切桩后桩基对管片作用力确定及控制措施

为获得盾构切除桥梁桩基后残桩对管片的竖向荷载及残桩的承载力，评估切桩后桥梁和盾构隧道结构安全，开展残桩对管片作用力的计算分析。首先，分析盾构切桩后残桩对管片作用力的影响因素，包括桩长减短、施工扰动及桥桩竖向刚度变化等。然后，在考虑这些因素影响的基础上建立残桩承载能力和所受竖向荷载计算公式，并以具体工程为例进行计算对比，结果表明： 本工程残桩承载力无法满足所受竖向荷载，需进行残桩周围地基加固；通过对地基注浆加固计算，残桩承载力可满足竖向荷载，能够保证管片和上部桥梁结构安全。最后，根据理论和实例分析，提出减小残桩对管片受力影响的施工控制措施，包括减小施工扰动、提高桩侧摩阻力及加强管片配筋和螺栓强度等。

Determination of Pile Foundation Force on Shield Tunnel Segments after Pile Cutting and Control Measures

To obtain the vertical load and vertical bearing capacity of the residual pile after removing the bridge pile foundation by shield cutting, the structural safety of bridge and shield tunnel after the pile cutting is evaluated, and the calculation and analysis on the force of residual pile on segment is conducted. First, the influence factors of residual pile on segment force after pile cutting by shield, including pile length reduction, construction disturbance and vertical stiffness change of bridge pile, are analyzed. Then, on the basis of influence factors mentioned above, the calculation formula for residual pile bearing capacity and vertical load is established, and is applied to project practice. The results show that the bearing capacity of the residual pile in this project cannot meet the vertical load requirement, which leads to grounting reinforcement of the foundation around the residual pile. The calculation results of foundation after grouting reinforcement show that the bearing capacity of the residual pile can meet the vertical load requirement, which ensures the safety of the segment and the upper bridge structure. Finally, according to the theoretical and practical analysis, the construction control measures to reduce the force of the residual pile on shield tunnel segment are proposed, including reducing the construction disturbance, improving the lateral friction of the pile and strengthening the rebars and bolts of segment.