在役桩网结构动力土拱损伤与拉膜耦合承载宏细观机理研究

The long-term cyclic loading of high-speed railway would lead to the repeated adjustments of arching effect and cushion tensioned membrane effect in pile-net structure, thus causing arching structure damage and cushion fatigue failure. This project, based on the combined researching methods of model test, dynamic triaxial test, numerical simulation and theoretical modeling, designs the new reduced-scale model tests of dynamic arching in pile-net structure by integrating transparent soil and PIV monitoring technology. By contrast, the numerical models of the particle flow mesoscopic mechanism are also established. Based on the quantitative evaluation of the macro-mesoscopic morphological evolution of arching structure, the damage mechanism of dynamic arching and the reinforcement effect of cushion tensioned membrane under cyclic loading can be explored. Thereby, the coupling bearing mechanism of dynamic arching and tensioned membrane effect is revealed gradually. Following the above-mentioned ideas, firstly, this project studies the damage stage division of dynamic arching on the basis of the evolution law of arching morphology. By further investigating the stress state of arching unit and the criterion for critical state of arching filling material, the damage criterion of arching degradation can be proposed and the macro-mesoscopic mechanical mechanism of dynamic arching damage can be revealed. On this basis, the space form and tension distribution of cushion in the process of dynamic arching damage is described quantitatively, and its reinforcement effect and resistance effect of dynamic load is further illustrated. Finally, by considering co-bearing mechanism of dynamic arching damage and tensioned membrane effect, this project builds a theoretical calculation model of pile-soil load sharing. The results of this research could enrich the carrying capacity theory of pile-net structure under dynamic loading, and provide technical support for improving the dynamic design method of pile-net structure.

高速列车长期循环荷载作用会导致桩网结构土拱效应和垫层拉膜的反复调整，引发土拱结构损伤和垫层疲劳破坏。本项目采用基于透明土和粒子成像测速（PIV）技术的动力土拱模型试验、填料动力特性三轴试验、颗粒流细观机制数值模拟以及理论建模相结合的方法，分析土拱结构形态的宏细观演化规律，研究循环荷载下动力土拱损伤过程和垫层拉膜的加筋机制，从而揭示动力土拱与拉膜效应耦合承载机理。遵循上述思路，通过查明土拱形态演变规律为定量划分动力土拱损伤阶段奠定基础；然后，确定填料临界状态的判别准则，分析拱体单元应力状态，进而提出土拱结构损伤的判别条件，揭示动力土拱的宏细观损伤机理；进一步，定量描述土拱损伤过程垫层拉膜的空间形态和拉力分布，研究垫层加筋作用和抗动效应；最后，建立动力土拱与拉膜承载耦合的桩土荷载分担计算模型。本研究成果将丰富桩网结构动力承载理论体系，为完善桩网结构动力设计方法提供支撑。

高速列车长期动循环荷载作用导致桩网结构土拱效应和垫层拉膜效应的反复调整和变化，引发土拱结构损伤失稳以及格栅垫层疲劳破坏。本项目采用桩网动力土拱模型试验、填料动力特性三轴试验、理论分析以及解析计算结合的方法，分析土拱结构形态的演化，研究动力土拱的损伤失稳条件，探讨垫层拉膜效应的荷载传递特征，揭示循环荷载下土拱与拉膜效应的耦合承载机制。本项目通过开展填料动三轴剪切试验，确定了填料处于稳定、临界、破坏状态的界限荷载，提出拱体材料临界状态的判别准则。然后，研发了循环荷载下桩网结构土拱损伤与拉膜耦合承载的缩尺模型测试系统，模拟循环荷载下基床-拉膜垫层-桩土之间的相互作用，监测了土拱结构形成演化过程，研究了动力土拱退化-重构、失稳破坏的演化规律，查明了动力土拱结构的损伤机制。在此基础上，描述了土拱损伤过程中垫层形态和拉力分布，研究了拉膜效应发挥对桩土荷载传递的影响规律，综合评价了循环荷载下土拱效应以及拉膜效应协同荷载传递的工作过程。最后，通过分析拱体单元应力状态，建立动荷载下土拱与拉膜综合承载的桩土荷载分担计算模型。本研究成果将丰富在役桩网结构动力承载理论体系，为完善桩网结构动力计算方法提供了技术支撑。