盾构穿切过程中单桩复合地基动态响应的研究

为探究盾构直接穿切复合地基对复合地基承载性状的影响规律，依托郑州地铁5号线某区间盾构穿切水泥土群桩复合地基工程，对盾构穿切单桩复合地基进行现场试验研究。分析盾构切桩全过程中地表沉降、桩顶压应力和桩间土应力的变化规律。同时，在与现场试验分析结果进行对比验证的基础上，利用数值模拟进一步对桩身轴力和桩侧摩阻力进行补充分析。主要结论如下： 1）在盾构穿切单桩复合地基全过程中，加载板沉降发展规律大体分为盾构切桩前、刀盘切桩、盾体穿越残桩、盾体脱离残桩、同步注浆层填充与凝结、残桩脱离盾尾6个阶段。2）桩土应力比随着切桩施工过程先减小后增大；桩身轴力随着整个切桩过程发生变化，最终阶段轴力值相比切桩前有所增大。3）由于残桩桩长变短，桩身应力重分配比使得桩身出现2个中性点，中性点以上为正摩阻力，桩体受压；中性点以下为负摩阻力，桩体受拉。4）与最终的累计量相比，各阶段加载板沉降增幅比分别为20%（盾构切桩前）、60%（盾构切桩—注浆层凝结）、20%（盾构远离残桩复合地基）；桩土应力比增幅分别为-8%、-16%、-53%、3%、25%、66%。

Dynamic Response of Single Pile Composite Foundation during Shield Tunneling

To investigate the influence of shield tunneling on the bearing behavior of the composite foundation, a case study and a field test are conducted on the shield tunneling through composite foundation of cement soil pile group in a section on the Zhengzhou metro line 5. The variation trends of the ground settlement, pile top pressure stress, and soil stress between the piles are analyzed for the entire process of shield tunneling via piles. Moreover, the pile shaft axial force and side friction are further analyzed using numerical simulations based on the comparison and verification with the field test results. The conclusions inferred from the present findings are stated as follows: (1) During the entire process of shield tunneling through single pile composite foundation, the development law of loading plate settlement can be generally classified into six stages, i.e., before shield tunneling, cutterhead cutting, shield tunneling through residual piles, shield tunneling away from residual piles, filling and condensation of synchronous grouting layer, and shield tail away from residual piles. (2) The pile soil stress ratio initially decreases but later increases with the pile cutting construction process; the axial force of the pile shaft varies with the pile cutting process, and the axial force value in the final stage increases compared with that before pile cutting. (3) As the length of the residual pile shortens, the stress redistribution of the pile body induces two neutral points on the pile body, above which the pile body experiences positive friction and compression, and below these points, it endures negative friction and tension. (4) Compared with the final cumulative settlement, the loading plate settlement in each stage increases by 20% before shield cutting, 60% during the condensation of the shield cutting grouting layer, and 20% for the shield situates farther from composite foundation. The increase ratio of the pile soil stress ratio is －8%, －16%, －53%, 3%, 25%, and 66%.