高速列车荷载引发主应力轴旋转路径下软土动力特性试验与理论建模研究

Chinese high-speed railway construction is developing rapidly. Ensuring the stability and controlling the long-term settlement of soft ground has become one of the key technologies of these projects. Under the high-speed train load, the stress path charactered with principal stress rotation will generate in the ground. It will influence the soil quiet different from the other stress paths. But the related research was seldom reported. The project is aimed to discover the macro and meso static and dynamic behaviors of soft clay under the coupling changes of principal stress orientation and amplitude with the hollow cylinder testing and micro telescopic testing. Meanwhile the evolution rules of characteristics of soft clay as well as the unified failure criterion under complicated stress paths will be revealed. Based on the experimental data and theoretical analysis, the relations and differences of non-coaxial characteristics for intact and remold clay will be discovered. Then the dynamic constitutive model will be established, which is suitable for the stress paths under the coupling change of principal stress orientation and amplitude. To verify and compare the laboratory testing results, the large scale model dynamic tests will be carried out. Finally with the testing data and mathematical analysis the mechanism of soil's cumulative plastic deformation in the soft substratum will be studied. Then the empirical calculation methods on soft clay's cumulative plastic deformation under high-speed train load will be established. These researches will contribute to the improvement on the theories of soil constitutive model under conplex stress paths and design of high-speed train construction.

我国高速铁路建设飞速发展，确保软基稳定和控制长期沉降是相关工程建设的关键技术之一。列车作用下，路基中产生主应力轴循环旋转的应力路径对软基土体产生显著且不同于其他动力路径的影响，但相关研究成果少见报道。本项目拟通过空心圆柱试验和细观结构电镜分析，揭示主应力轴循环旋转与应力幅值耦合变化下软土宏细观静、动力特性与复杂动力路径下软土性状演变规律，建立相关路径下软土破坏统一评价准则；结合试验数据，通过理论分析，揭示各种复杂应力路径下饱和原状和重塑软黏土的非共轴特性关联与差异，建立可综合反映包括主应力方向旋转与应力幅值耦合在内的复杂应力路径下的软黏土动力本构模型；开展大型模型槽动力试验，基于室内外试验结果对比修正，结合数值分析，系统研究软弱下卧层土体的累积变形机理，建立列车荷载下软土地基长期沉降变形计算与控制方法。研究成果将对完善复杂路径下土力学本构体系和高速铁路工程设计理论具有重要参考价值。

针对高速列车荷载作用的软弱下卧层土的工程问题，通过室内空心圆柱单元体试验和室外大型模型槽试验以及理论分析、数值仿真等手段，对高速列车荷载引发主应力轴旋转路径下软土动力特性试验与理论建模进行了系统的研究。（1）项目对饱和软黏土的基本动力特性试验与机理进行了分析研究，探究原状软黏土和重塑软黏土在静、动态主应力轴旋转条件下剪胀特性以及临界状态特性，分析了频率和动应力比对竖向累计变形及累积孔压的影响，建立了列车荷载下土体的塑性累积模型和孔压模型，基于列车荷载下地基土孔压-应变发展曲线进行分析，利提出了新的破坏标准。（2）研究了高速列车荷载作用下饱和软黏土应力应变非共轴关系建模及本构理论，建立了考虑频率、动应力比对非共轴与大主应力方向角关系曲线形态变化影响的非共轴模型，采用分数阶微分和传统塑性力学的交叉，对屈服进行分数阶微分，建立分数阶非关联流动法则，假定土体屈服面服从各向同性硬化，基于分数阶梯度律，建立分数阶塑性硬化模量，基于所提出分数阶塑性流动法则和塑性模量，建立分数阶塑性力学本构关系，在该边界面函数中插入组构张量，提出考虑非共轴角影响的各向异性边界面本构模型。（3）开展地基的长期沉降变形机理与计算方法的研究，利用大型土工模型试验槽，开展了复合地基动力试验模型研究，建立了列车荷载下复合地基的归一化沉降与归一化荷载循环次数之间的函数经验模型，有助于根据现场沉降情况预估长期沉降，将本构模型二次开发入有限元数值软件中，建立基于动力有限元分析的饱和软黏土长期变形理论计算方法。