软土盾构法隧道纵向应力松弛的发生机理及其效应

It is found that the longitudinal instability of shield-driven tunnel, which is featured with instable time-lasting deformation and varying load bearing conditions in soft ground, is closely related to the longitudinal stress degradation observed in-between lining rings both at construction and service stages of tunnels. This proposal focuses specially on the scientific study of key issues involved in the longitudinal stress relaxation: the origination and evolution of longitudinal stress relaxation as well as their effects on the long-term stability of tunnels in soft ground. Field and laboratory tests, as well as numerical modeling and analytical methods are all used in order to conduct a comprehensive and in-depth study. The proposed study is: (1) to analyze the variation and discontinuity of contact state between adjacent lining rings induced by the original gaps and those discrepancies generated in the assembly procedure of segment lining, and also to make clear their correlations and interactions with the longitudinal stress relaxation; (2) to create mechanical models for stress relaxation on the contact surface and bolts between adjacent rings respectively, as well as creep-relaxation coupling model for the contact surface between lining and soils; and then to construct an integrated model of the entire ring based on the above elemental models. (3) to define and solve the criterion equations for critical deformation state and load bearing state of ring-ring contact surface accounting for the effect of longitudinal stress relaxation. (4) to apply numerical modeling incorporating the above elemental models and criterion to simulate more accurately the changing states of surface contact under longitudinal stress relaxation and its effect on the longitudinal stability of tunnel rings, thus to further explore the evolution mechanism of tunnel lining stabilizing process from its assembly to becoming stable in ground, which is achieved by the adjustment of the surface contact state between rings; and finally to solve the longitudinal stability of segmental tunnel and its time dependent problems substantially. The present study is of great values not only in science, but also in engineering practice, optimizing the geometry design of tunnel ring-ring face and control of shield driving and segment assembly procedure.

实践表明，盾构隧道纵向长期承载及变形的非稳定性与其衬砌环间应力及接触状态密切相关。课题围绕隧道纵向环间应力松弛的发生机理这一核心问题展开研究，采用工程实测、模型实验、数值模拟和理论解析相结合的研究方法，分析隧道衬砌环缝几何构造及衬砌拼装过程所致典型非连续几何接触状态、及其与纵向应力松弛的相互影响过程及相互关系，推导衬砌环面接触应力、纵向螺栓应力的松弛模型以及衬砌-土体接触蠕变松弛模型等三种要素模型，在此基础上构建衬砌环整体松弛模型；推导、求解基于应力松弛的环间临界承载和变形状态方程；采用基于上述模型和状态方程的数值方法定量分析应力松弛导致的隧道衬砌环间几何接触状态的变化规律及隧道纵向承载、变形特性，从而揭示隧道结构本体从形成到稳定的演化过程与力学机制，从本质上解决隧道纵向稳定的临界与时变问题；课题的研究对于管片衬砌隧道环间构造设计、盾构掘进与衬砌拼装控制等均有重要的理论指导意义和实用价值。

盾构隧道纵向长期承载及变形的非稳定性与其衬砌环间的纵向应力密切相关。围绕盾构隧道纵向应力松弛的发生机理及其效应展开研究。首先通过现场试验揭示了纵向应力松弛的阶段性及其演变规律，然后研究了纵向应力松弛的发生机理。在此基础上，构建了盾构隧道纵向应力松弛的理论计算模型。最后进一步推导了基于应力松弛的隧道衬砌环缝抗剪及接缝渗漏的计算模型。.主要结论如下：.（1）分块管片拼装后的实测内力经历了平稳变化、波动或急剧跳跃后逐渐逼近理论值；盾构隧道纵向应力在管片拼装后将经历周期性波动、持续衰减、相对稳定、加速衰减四个阶段的演变，期间，隧道结构顶部的纵向应力松弛最为明显、腰部次之、底部最小，应力松弛度最大可达80%。.（2）盾构隧道纵向应力周期性波动阶段持续时间相对较短，且在该阶段受千斤顶推力较大等的影响，纵向应力可能出现短期内增大趋势；持续衰减阶段是纵向应力调整的关键阶段，持续时间超过半年，若计入施工期发生的纵向沉降影响后，该阶段的持续时间将进一步延长；后期发生的不均匀沉降导致纵向应力可能由相对稳定阶段转入加速衰减阶段，最终造成隧道失稳破坏。.（3）盾构隧道纵向应力松弛受隧道接缝几何接触条件变化、隧道结构本体材料应力松弛和外部环境变化的多重影响。考虑隧道纵向应力松弛和密封垫防水性能弱化的共同影响后，衬砌环间渗漏水更为严重。.主要创新性工作如下：.（1）通过对隧道管片拼装及运营阶段纵横向应力的全过程连续监测，并结合数值模拟分析，揭示了盾构隧道纵向应力松弛的发生机理。.（2）考虑盾构隧道结构的非连续性及其与地基接触关系的时变特性，推导建立了考虑地基水平剪切蠕变的粘弹性地基梁模型，从理论上分析阐明了盾构隧道纵向应力松弛的力学本质及其规律。.（3）建立了盾构隧道在纵向应力松弛条件下的接缝渗流量及抗剪承载的计算模型，并据此分析得到了接缝渗漏水和环间抗剪性能的时变规律。