考虑近期应力历史对土体小应变刚度影响时双线盾构隧道施工引起的地表变形研究

With the densification of urban subway lines, it is often required to excavate twin tunnels, such as parallel tunnels, overlapped tunnels underneath existing buildings, running railways et al., where ground deformation is strictly limited. Due to the superposition of tunnelling effects, it is more difficult to control the ground deformation induced by the construction of twin tunnels when compared with that of a single tunnel. Therefore, it is of great importance to accurately predict twin-tunnelling-induced ground deformation. It has been proved that the recent stress history significantly affects the small strain behavior of soil, and hence plays an important role in the prediction of tunnelling-induced ground deformation. However, previous studies on the construction effects of twin shield tunnels do not take the influence of recent stress history into account, which makes it difficult to achieve accurate prediction and control of the ground deformation..In this study, laboratory triaxial tests will be performed first following the true stress path of the soil during shield tunnelling, to investigate the influence of recent stress history on the small strain behavior of soil and to improve currently existed constitutive models. After that, by incorporating numerical modelling, centrifuge tests as well as in situ measurements, the ground deformation induced by the construction of both single and twin shield tunnels will be studied, on basis of which subtilized methods for controlling the ground deformation induced by the construction of twin shield tunnels can be proposed to guarantee the safety of surrounding environments.

城市地铁线路网络渐趋密集，经常出现隧道近接既有建筑物、已运营铁路等施工的情况，地表变形控制要求严格。与单条隧道施工相比，双线隧道施工因涉及两条隧道施工影响叠加，变形控制更加困难，故精确预测双线隧道施工引起的地表变形尤为重要。已有研究表明，土的近期应力历史对土体小应变刚度影响显著，是预测隧道施工变形所要考虑的关键因素。双线隧道采用盾构法施工时，会在土中形成复杂的应力历史，影响两隧道施工期间土体刚度及变形行为。目前关于双线盾构隧道施工引起的地表变形研究均未考虑施工期间应力历史的影响，难以实现地表变形精细预测。.拟首先开展室内三轴试验，研究盾构施工扰动下土的应力历史对小应变刚度的影响，改进现有本构。而后，结合数值模拟、现场实测及离心机试验，研究单条及双线盾构隧道考虑施工扰动下土体应力历史影响时的地表变形规律。在此基础上，提出双线盾构隧道施工地表变形的精细化控制方法，保证双线盾构施工周边环境安全。

城市地铁线路网络渐趋密集，经常出现隧道近接既有建筑物、已运营铁路等施工的情况，地表变形控制要求严格。与单条隧道施工相比，双线隧道施工因涉及两条隧道施工影响叠加，变形控制更加困难，故精确预测双线隧道施工引起的地表变形尤为重要。已有研究表明，土的近期应力历史对土体小应变刚度影响显著，是预测隧道施工变形所要考虑的关键因素。双线隧道采用盾构法施工时，会在土中形成复杂的应力历史，影响两隧道施工期间土体刚度及变形行为。..首先开展了室内三轴试验，研究了复杂应力历史对土体小应变刚度的影响机理。而后结合单条隧道施工各阶段周围土体应力路径特点，分析了单条盾构隧道施工各阶段土层刚度变化情况及其对地表沉降的影响。研究表明：根据隧道周围土体应力路径特点，盾构施工可分为掌子面到达前、掌子面经过后以及盾尾经过后三个阶段。对于拱顶和拱底土体，三个阶段相邻阶段由于应力路径方向改变较为明显，均出现刚度骤增，对隧道上方土体沉降有一定的抑制。而对于拱腰处土体，在掌子面到达前以及经过后这两个阶段表现出应力路径延续，刚度持续衰减，软化明显。因此，隧道两侧土体产生更多指向隧道中心的位移。..在单条隧道研究基础上，开展双线隧道模型试验及数值模拟，研究了先建隧道施工在土中产生的应力历史对后建隧道施工时地表变形的影响。研究表明：对于不在同一埋深的双线隧道，上线隧道先开挖会导致下线隧道拱腰和拱肩土体软化，下线隧道开挖时就会产生更多指向下线隧道的位移，最终引起地表沉降槽更深窄；下线隧道开挖会导致上线隧道拱腰及拱肩（靠近下线隧道一侧）土体软化，上线隧道拱顶处土体硬化，最终引起地表沉降槽更浅宽。..本项目基于土体对于复杂扰动具有记忆特性并将对后续变形行为产生影响的观点，从全新的角度揭示了双线盾构隧道施工引起的地表变形规律及机理。研究成果可助于推动和创新精确预测双线盾构隧道施工对地层及周边环境的影响，以及实现双线盾构隧道施工变形的精细化控制。