地震液化诱发地铁结构上浮的机理及数值分析方法研究

Sand liquefaction is a typical hazard during the earthquake, which brings huge damages to the structures and facilities, such as ground settlement, lateral spreading and so on. So that seismic liquefaction of saturated sand is a hot topic in the current few decades. The special design should be proposed when the subway route pass through the liquefiable area, among which, the uplift of subway structure is a key issue. In this project, based on the practical project, model test, theoretical analysis and numerical simulations will be conducted to analysis the mechanism of subway uplift response. A shaking table test system and a FEM-SPH coupled method will be developed to simulate seismic liquefaction and subway uplift behaviors, meanwhile, an adaptive stepping method will be embedded to adapt the earthquake load with the characteristics of randomness. The proposed adaptive FEM-SPH method can improve the calculation accuracy and efficiency. The main research content is as follows: (1) Subway internal models with rectangle, circular and horseshoe-shaped sections are established respectively, the influence of section type, buried depth, earthquake intensity, liquefaction degree, as well as the uplift mechanism will be studied. (2) Through the proposed numerical method, the anti-liquefaction and anti-uplift project measures such as tensile pile, cutoff wall, and grouting reinforcement are verified and compared. It will propose an optimized anti-liquefaction strategy for the practical project. Through this project, it can provide scientific proofs for the subway aseismic design and safety assessment, with great benefit to scientific research and engineering application.

饱和砂土地震液化会造成地基沉降、液化土横向流动等灾害，是目前研究的热点课题。当城市地铁穿越可液化土层时，需进行专项设计，但是液化土与地铁的相互作用机理尚不明确。本项目以实际工程为背景，从模型试验、理论分析和数值模拟三方面入手，研究地铁结构液化上浮的机理，拟研制一套可模拟液化场地中地铁结构上浮响应的振动台试验系统，同时开发有限元-无网格耦合的数值方法模拟液化土体大变形及结构响应，引入自适应步长法适应地震荷载的随机性，提高计算的精度和效率。主要研究内容有：（1）对矩形、圆形和马蹄形三种区间断面模型进行分析，研究断面型式、埋置深度、地震强度、液化程度等因素对上浮响应的影响，探究地铁结构液化上浮的机理及分析方法。（2）研究抗拔桩、隔离墙、注浆加固等抗浮措施的作用机理和效果，比选三种抗浮方案及设计参数，提出最优的抗液化措施。通过本项研究可为地铁抗震设计提供参考依据，具有一定的科学意义和工程应用价值。

饱和砂土地震液化会造成地基沉降、液化土横向流动等灾害、地下结构上浮等灾害，且修复难度大，经济损失严重。当城市地铁穿越可液化土层时，需进行专项设计，但是液化土与地铁的相互作用机理尚不明确。本项目从理论分析、数值模拟、工程技术研发等方法开展研究。主要研究内容及取得的成果如下：（1）采用循环弹塑性动力本构模型模拟液化地层的大变形特性，同时开发了自适应步长数值方法，对地铁结构液化上浮的机理开展相关研究，获得了表征场地液化程度的超孔隙水压力比分布规律，揭示了液化上浮响应与液化程度的关系。（2）研究了抗拔桩与隔离墙抗浮效果，对比分析了抗浮桩长度、隔离墙距离等多种影响抗浮的因素，发现抗浮桩需打入非液化地层才能起到良好的抗浮效果。地表的变形呈现明显的“几”字形，通过抗拔桩与隔离墙的加固，“几”字形变矮，地表隆起变形得到了明显改善。（3）采用自适应步长算法，获得了数值计算的位移误差及孔压误差分布规律，通过混合误差控制，有效提高了计算的精度，节省了计算时间。（4）研发了新型抗浮桩、新型抗浮锚杆等地铁车站抗液化上浮的工程措施。抗浮桩采用抗拔桩和排水砂桩组合布置，一方面可以对液化场地进行快速超孔隙水压力消散，另一方面抗拔桩起到对地下车站的锚固力。本项研究的科学意义为：（1）解决了液化大变形动力数值计算中计算精度和计算误差矛盾的问题，合理优化了计算资源。（2）探究了地铁结构在液化场地发生上浮响应的机理，为下一步研究结构损伤提供了相关依据。（3）开发了抗浮的技术措施，在今后的工程中可以参考应用。