小半径隧道的转弯半径越小，超挖量越大。为减少超小半径曲线盾构隧道施工中的地层扰动，探索无超挖刀掘进技术的可行性，提出一种基于盾体几何参数优化的无超挖掘进方法，无需使用刀盘超挖刀，依靠刀盘与盾体直径差提供转弯所需空间，相比传统超挖模式可减少内侧超挖量。首先，建立超小半径曲线盾构隧道的几何约束模型，推导无超挖条件下前盾长度的定量确定方法； 其次，提出盾构关键参数的设计； 然后，建立基于优化盾构的掘进控制策略； 最后，结合110 m级小半径工程实例，验证该技术路径的可行性。结果表明： 1）对于超小曲线半径盾构施工，通过建立几何约束模型，充分利用刀盘与盾体的直径差，可实现无超挖模式盾构施工。2）优先选择可实现大铰接角度的主动铰接，铰接位置选择盾构中部可保证尾盾的转弯能力。3）盾构进曲线段后维持稳定的铰接姿态，姿态微调主要依靠推进千斤顶实现，减少控制变量； 隧道腰部土体的沉降趋势会随盾构掘进发生转变。
As the turning radius of a tunnel decreases, the overcut volume increases during shield tunneling. To reduce ground disturbance in shield tunneling with ultra-small turning radii and explore the technical feasibility of tunneling without over-cutters, a overcut-free tunneling method based on the optimization of shield geometric parameters is proposed. This method requires no over-cutters installed on the cutterhead, and utilizes the diameter difference between the cutterhead and the shield body to create the space required for curve turning. Compared with the conventional overcut mode, it can reduce the overcut on the inner curve side. First, a geometric constraint model for shield tunneling in ultra-small radius curves is established, and a quantitative method for determining the front shield length under overcut-free conditions is derived. Second, the design of key shield parameters is proposed, and subsequently, a tunneling control strategy adapted to the optimized shield is formulated. Finally, a case study is conducted on a tunnel with a turning radius of 110 m, verifying the feasibility of the proposed technical scheme. The results show that: (1) For shield construction in ultra-small radius curves, the overcut-free construction mode can be realized by establishing the geometric constraint model and fully utilizing the diameter difference between the cutterhead and the shield body. (2) Active hinge that allows a large hinge angle is preferred. Setting the hinge joint at the middle part of the shield can guarantee the turning capacity of the tail shield. (3) After the shield enters the curved section, the hinged posture shall be kept stable, and fine attitude adjustments are mainly completed by thrust jacks to reduce control variables. The settlement trend of soil at the tunnel springline changes continuously with shield advancement.
