砂卵石地层隧道近接高层建筑施工的影响分区研究

This application will carry out a study on influence partition of tunnel (excavated by mining method) approaching to existing high-rise building in sand and gravel stratum, by using methods of theoretical analysis, numerical simulation and model test. First, changing the initial stress field will be used to simulate different depths, revealing transfer mechanism and their failure characteristics of structure-controlled failure and stress-controlled failure in sand and gravel stratum. Then tunnel support concept of heavy support for soft rock and light support for granular material will be put forward. For sand and gravel stratum with high content of large particle size, light support system considering full use of rock mass strength will be studied. In addition, the interaction mechanism of support and surrounding rock will be analyzed microscopically and macroscopically. On this basis, the study will be extended to more complex environment of tunnel approaching to existing high-rise building. Mechanical behavior will be compared when tunnel in different positions near building foundation. Then influence degree will be defined according to a certain criterion and threshold. After that, mathematical statistics method will be used to deal with the discrete calculation results. Consequently, influence partitions of non-supported (i.e., support failed) case and light supported case will be respectively formed. At last, research findings of the project supported by the Young Scientists Fund of NSFC will be introduced, in order to establish relationship between influence partitions in granular material and that in continuous medium material considering the macro equivalent physical properties. The achievements may provide guidance for design and construction of related projects, and also provide theoretical and technological support for establishment of standards in the future.

通过理论分析、数值模拟、室内模型试验等方法，对砂卵石地层矿山法隧道近接高层建筑施工的影响分区进行研究。首先通过改变初始应力场来模拟不同埋深的影响，揭示散体围岩结构控制型破坏与应力控制型破坏的转换机理及其破坏特征，进而提出“怕软不怕散”的隧道支护理念，对于大粒径砂卵石地层探索充分利用岩块强度的轻型支护体系，并对支护与围岩的相互作用机理进行细、宏观分析。在此基础上，推广到新建隧道邻近既有高层建筑施工这一近接施工类型，对比分析隧道处于建筑物基础附近不同部位时的力学行为，并根据一定的判别准则和阈值划分影响程度，再用数学拟合方法从点到面，形成无支护（即支护失效）与有支护工况下的影响分区。最后引入青年科学基金项目研究成果，建立散体材料与考虑宏观等效物理属性的连续介质材料之间的影响分区联系。研究成果可为相关工程的设计与施工提供指导，也为今后规范标准编制提供理论和技术支撑。

砂卵石地层在我国各大城市分布广泛。作为一种散体颗粒材料，这种地层主要表现为颗粒粒径大，离散性强，单体强度高，非连续力学特征明显。然而，目前工程设计并未细致考虑“松散但质硬”和“完整但质软”两类围岩的力学差异，对该地层隧道近接建筑物施工的风险研判亦缺少通用性标准参考，仅限个案研究。本项目结合理论分析、数值模拟、模型试验等方法，对砂卵石地层的工程特性以及该地层新建隧道近接既有高层建筑施工的影响分区标准进行了研究。主要成果如下：（1）在经典“粮仓效应”的基础上，开展了砂体斜坡竖向自重应力分布的试验研究，揭示了颗粒接触力链拱效应和坡顶应力凹陷现象；提出了砂卵石材料分别基于颗粒细观力链稳定和基于宏观摩尔库伦强度准则控制的破坏模式转换条件，以及工程上结构控制型破坏与应力控制型破坏的转换临界埋深；建立了成都砂卵石颗粒计算所用细观参数与连续介质宏观本构模型参数的定量关系；（2）针对有约束的砂卵石工程特性，开展了格宾卵石笼试件的单轴（无侧限）压缩试验，得到了全过程应力-应变曲线，以及卵石笼单轴压缩峰值强度与格宾网、填料（砂卵石）之间的定量关系，体现了有约束的砂卵石具有很好的承载能力。进而提出了“怕软不怕散”的隧道支护理念，对于大粒径砂卵石地层建议采用能辅助散而硬的围岩形成承载拱的轻型支护体系，充分利用颗粒强度。通过砂卵石地层隧道不同支护厚度的极限承载力模型试验，验证了散体成拱后承载的主体是围岩本身，不同支护厚度的极限承载力差异不大；（3）分别建立了无支护（即支护失效）和轻型支护条件下的砂卵石地层新建隧道邻近既有高层建筑施工的近接影响分区标准，为预判该类工程的安全风险和控制对策选用提供依据。在此基础上，引入青年基金项目硬岩影响分区成果和日本规范相关规定，总结分析了相互之间的联系与区别。上述研究成果可为砂卵石地层隧道的设计与施工提供理论与技术支撑，也可为今后相关规范指南编制提供参考。