高填黄土减载明洞土拱效应时效性演变规律及衬砌结构长期安全状态研究

In order to meeting the city area of the Loess Plateau region and demanding of the traffic construction land, the high fill loess open cut tunnels are increased.Load reduction measures form soil arching effect on the top of open cut tunnel,changing the mechanical and deformation behavior. However, the creep behavior of loess, EPS plate and geogrid makes soil arching effect,mechanical and deformation of lining structure in the dynamic change, which affect the long-term safety of the structure. Researching the timeliness of soil arching effect of high fill loess load reduction open cut tunnel with laboratory test and numerical simulation, and the lining structure mechanics, deformation behavior and safety are obtained which consider the time effect. Obtaining the creep behavior of loess and load reduction materials through laboratory test, the creep model is established and the parameters are determined. On the premise of similarity theory, the model test of EPS plate and geogrids of high fill loess open cut tunnel is conducted considering the creep behavior of soil and load reduction materials. The model test and numerical analysis results are verified mutually,then conduct the systemic finite element calculation to obtain the change rule of soil arching effect, lining structure mechanics, and deformation behavior of high fill loess open cut tunnel load reduction considering the effect of time. Finally, comprehensive analysis of long-term safety state of lining structure through variation of safety factor, principal stress, crack occurrence and distribution with time in different positions of lining structure.

为满足黄土高原地区城市及交通建设用地需求，高填黄土明洞日趋增多。减载措施促使明洞顶部形成土拱效应，改变其受力和变形性能。然而，黄土、EPS板、土工格栅的蠕变共同作用使得土拱效应、衬砌结构受力和变形处于动态变化中，影响结构长期使用安全。本课题采用室内试验和数值模拟相结合的方法，研究高填黄土减载明洞土拱效应的时效性，并进一步得到考虑时间效应的衬砌结构力学、变形性能及其安全状态。通过室内试验，得到黄土及减载材料蠕变特性，建立其蠕变模型，并确定参数取值；以相似理论为前提，考虑填土、减载材料蠕变特性，进行EPS板+土工格栅减载的高填黄土明洞模型试验；将模型试验和数值分析结果相互验证；随后进行系统的有限元计算，获得考虑时间效应的高填黄土减载明洞土拱效应和衬砌结构力学、变形性能变化规律；最后，通过衬砌结构不同位置截面安全系数、主应力、裂缝发生及其分布随时间的变化规律，综合分析衬砌结构长期安全状态。

在我国“一带一路”战略背景下，中西部黄土地区工程建设将迎来高峰。而在黄土地区沟壑纵横的地形地貌，以及错综复杂的交通线路的共同影响下，高填方明洞工程的出现难以避免。对于黄土地区的高填方明洞，当采用重塑黄土进行回填时，考虑到重塑黄土尽管在回填时重新压实，但其蠕变性质仍然明显，可能会对高填方明洞衬砌长期安全性产生一定影响。为此，本文通过数值模拟方法，考虑高填方明洞回填黄土蠕变，探究高填方明洞长期力学性能演化规律。结果表明，在回填料蠕变的基础上进一步考虑减载材料蠕变后，高填方明洞衬砌内力、变形随时间仍将经历“不稳定变化状态、不稳定变化状态逐渐消失、内力优化、变形恢复”的变化过程。不稳定变化状态下，衬砌内力、变形因铺设减载材料而产生的变化量随时间增长基本保持恒定，减载效果未发生显著变化。而不稳定变化状态消失后，随时间继续增长，衬砌内力、变形因铺设减载材料而产生的变化量总体趋于减小，减载效果下降。