循环移动列车荷载下路基应力状态变化及安定分析

With breathtaking development of China railway network, current trackbed design method needs to be improved in terms of rationality and flexibility. Controls on train-induced trackbed settlement are mainly based on empirical equations and elastic theory, therefore characteristics of trackbed plastic deformation due to sophisticated train-induced stress state variation have not been well revealed. In this project, firstly, elastic-plastic finite element simulations of trackbed subjected to repeated moving train loads will be carried out to analyse development of residual stress field in the trackbed. Effect of residual stresses on stress state variation of soils will also be investigated. Then, shakedown analysis will be undertaken based on lower bound shakedown theorem and characteristics of residual stress field in the trackbed. Shakedown limits obtained through shakedown analysis can be used to predict the trend of accumulated plastic deformation in the trackbed. After that, a series of drained HCA tests will be carried out under various stress paths to examine the influences of residual stresses and load magnitudes on the trend of cumulative plastic deformation. This trend will also be compared with predictions from shakedown analysis. Finally, a shakedown-based trackbed design programme will developed. This project will reveal characteristics of train-induced trackbed plastic deformation and its results can also be used to serve as a new theoretical basis for trackbed design.

国家铁路建设事业的蓬勃发展对铁路路基设计的合理性和灵活性提出了更高的要求。目前对于铁路路基在长期列车荷载作用下的工后沉降的控制，一般采用经验方法和弹性理论，因此不能反映复杂应力状态变化带来的路基累积塑性变形的本质。本项目拟通过弹塑性数值模拟系统分析循环移动列车荷载作用下路基中残余应力的分布和发展，揭示残余应力在铁路路基中的产生机理和分布规律；研究路基土单元应力状态随残余应力发展而产生的变化；基于下限安定理论对铁路路基沉降问题进行安定分析，结果可用于预测路基塑性变形趋势；通过空心扭转仪实验研究不同大小列车荷载及残余应力对塑性变形累积趋势的影响，并与安定分析的预测结果进行比较；最后编制一套基于安定分析的铁路路基设计程序。项目研究成果将对正确认识长期列车荷载所引起的路基累积塑性变形，以及建立新的铁路路基设计方法具有重要意义。

铁路路基在循环移动列车荷载下的塑性累积变形是导致路基沉降的一个重要因素。本项目采用数值模拟、理论分析和室内试验等方法从多方面研究了铁路路基土在循环移动列车荷载下的应力状态变化及其塑性应变累积情况。通过三维和二维数值模拟，研究获得了铁路路基中塑性应变和残余应力的分布及其变化规律，并提出了判定路基结构是否安定的数值经验方法。基于数值模拟结果，研究建立了一套求解无砟轨道路基安定极限的方法，适用于准静态情况和动力情况，进而揭示了影响准静态安定极限和动力安定极限的主要因素及其影响规律，包括弹性模量、内摩擦角、剪胀角、层厚、临界波速和列车速度等。通过动力空心扭剪试验模拟典型路基结构中地基土关键点的应力路径，研究获得了不同列车荷载幅值下关键位置砂土的塑性累积应变与塑性应变增量，证实了安定分析所获得的安定极限值。此外，研究还揭示了变化围压对塑性累积应变的影响规律。研究最后提出了基于安定理论的铁路路基设计方法，发展了铁路路基长期稳定性理论，并为未来铁路路基设计提供参考。