摘要:
盾构管片拆除会打破环间纵向压紧平衡状态，造成推力损失，继而诱发结构变形及环缝渗漏水，是西安地铁穿地裂缝设防段采用“先盾后扩”建造面临的关键难题之一。本文自研加载平台开展1:10比尺模型试验，探究管片拆除下推力损失和环缝张开量变化规律，分析螺栓二次预紧、拉紧措施范围、刚度以及组合措施的加固效果，并基于试验数据对既有纵向应力传递完整管模型进行修正。结果表明：距拆除位置越近，推力损失越大，残余推力总体服从指数分布。管片拆除引起的最大环缝张开量可达4.1mm，会造成设防段两侧管片防水性能降低。螺栓二次预紧仅能改善残余推力分布均匀性，对环缝张开量作用不大。型钢拉紧措施对减小推力损失率、改善推力均匀性和减小环缝张开量均有效果，但并不随拉紧范围或拉紧刚度增大而成比例改善。采用“14b槽钢拉紧10环+螺栓二次预紧”组合措施与“14b槽钢拉紧15环”或“16b槽钢拉紧10环”的效果基本相同。为定量给出管片拆除下推力损失影响范围，基于刚度串联原理，推导了考虑环缝效应的纵向应力传递优化模型，给出的推力传递规律更符合模型试验结果和工程实际，给出的纵向影响范围仅为完整管模型约1/10。环缝效应的本质在于放大管片—地层间纵向相对位移梯度，进而增大应力传递梯度，最终改变纵向推力传递路径和影响范围。
Abstract:
The removal of shield segments disrupts compressive equilibrium between tunnel rings, triggering thrust loss that induces structural deformation and ring joint leakage. This poses a critical challenge for fortification section of Xi’an Metro, constructed through ground fissures using the "shield before expansion" method. To investigate thrust loss and ring joint openings induced by segment removal, a 1:10 scale model test was conducted using a custom-designed loading platform. The efficacy of multiple reinforcement measures—including bolt re-tightening, variable tensioning ranges/stiffness, and combined strategies—was evaluated. Experimental data informed a revision of the conventional whole-pipe longitudinal stress transfer model. Results show that: Thrust loss intensifies proximal to the removal zone, with residual thrust stress following an exponential distribution. Segment removal induces ring joint openings up to 4.1 mm, significantly degrading waterproofing integrity on both sides of the fortification section. Bolt re-tightening improves residual thrust stress uniformity but minimally mitigates joint openings. Channel steel tightening measures are effective in increasing residual thrust stress, enhancing stress uniformity, and reducing ring joint opening. However, these improvements do not increase proportionally with the tensioning range or stiffness. Using a combination measure of "14b channel steel tightening 10 rings + bolt re-tightening" achieves the same effect as either "14b channel steel tightening 15 rings" or "16b channel steel tightening 10 rings." An optimized longitudinal stress transfer model, incorporating ring joint effects via series-stiffness principles, was derived to quantify thrust loss influence ranges. This model aligns more closely with test data and field observations, indicating a longitudinal influence range 1/10 of the whole-pipe model's estimate. Fundamentally, ring joint effects amplify the longitudinal segment-ground displacement gradient, elevating stress transfer gradients and altering thrust transmission paths and influence extents.
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