铁路碎石道床-土质基床界面接触应力的随机多尺度分析

The underline structure with ballast bed of crushed stone and subgrade bed of fine-grained soil, which occupies a fairly large proportion in the existing ordinary railways of our country, is frequently troubled by a variety of subgrade diseases. The dynamic stress of the rail subgrade surface (the interface between the ballast bed and the subgrade bed) is one external factor causing subgrade diseases. Currently, the stress of subgrade surface under train load is usually obtained through macroscopic hypothesis analysis on ballast bed. This method is not able to reflect the microscopic characteristics of the contact between ballast and subgrade bed soil. Nor can it show how the shape and the grain size of ballast randomly distributed influence the interface contact behavior. Therefore, compared with the actual loaded condition, some local significant information of contact stress is probably neglected, which may then cause deviation of the research on subgrade bed disease. To this end, this project, taking random shape characteristic and particle size distribution as the principle line, plans to carry out systematic research by means of the testing technique of diaphragm pressure distribution, the DEM-FEM coupled multiscale numerical method, the probability stochastic simulation and other research tools. This project proposes to reveal the internal force transfer rule of the ballast particle under cyclic loading and the dynamic evolution of the contact characteristics between the discrete ballast and the continuous soil, ascertain the behavior and the random variation characteristics of the “discrete type” contact stress of the surface between ballast and subgrade bed soil, and establish a probability model considering the maximum contact stress and other factors. The research result will offer a scientific criterion to forecast, prevention and treatment of the railway subgrade disease.

碎石道床-土质基床直接接触作用的这种结构形式在既有普通铁路中占比大，并产生了大量基床病害。列车荷载下道床-基床界面（路基面）动应力是引起基床病害的重要因素。目前基于对道床的宏观假设分析得到的路基面应力，由于不能反映道砟-基床土两种介质接触的细观特性，也不能体现随机分布的道砟形态、粒径等对界面接触行为的影响，其与路基面真实受荷环境相比，可能会忽视某些局部重要的接触应力信息，从而引起基床病害研究上的偏差。本项目以道砟颗粒离散性和随机性特征为主线，融合薄膜压力分布测试技术、离散元-有限元多尺度数值方法、随机概率模拟等手段，揭示循环加载下道砟颗粒体系内力传递规律和道砟-基床土两种介质接触细观动态演化这一科学问题，探明道床-基床界面“离散型”接触应力特性和随机变异规律，建立最大接触应力等的概率分布模型，改变目前采用连续性分布描述、确定性方法量化路基面应力存在的不足，为基床病害预测和整治提供科学依据。

围绕铁路碎石道床-土质基床界面接触应力的连续-非连续介质接触问题，基于罚函数方法，引入界面单元实现不同求解域间数据交换，采用开源有限元程序OOFEM以及离散元程序YADE，在集成程序MuPIF框架下开发了离散元-有限元界面耦合计算程序。针对道砟颗粒随机形态量化表征问题，基于离散点局部曲率提出了道砟颗粒局部形态特征指标——曲率指数（Curvature Index, CI）来定量表征颗粒棱角特征。在此基础上，基于本征正交分解与径向基神经网络提出了满足颗粒整体及局部形态指标概率密度分布的道砟库的重生成算法。采用该方法重构道砟颗粒的形态特征指标统计结果与扫描试样结果接近。开展了碎石道床-土质基床室内模型试验，采用矩阵式薄膜压力分布测试技术测试道床与基床面接触应力的分布规律，分析路基面上最大接触应力以及轨枕下方平均应力。揭示了路基面离散型应力分布，且应力集中现象显著，远高于传统土压力盒测试结果。结合试验结果，基于道砟颗粒形态指标概率密度分布函数，建立了铁路轨枕-道床-土质基床DEM-FEM三维动力耦合模型，从细观角度揭示了列车荷载由道床到路基表面的传递特征，以及分析了颗粒运动与棱角对接触应力的影响。统计得到不同列车轴重作用下路基面峰值应力与平均应力的正态分布规律，预测了路基面应力最大值。本研究量化了碎石道砟随机形态特征，揭示了道砟与基床界面接触“离散型”分布机理，为有砟铁路基床病害精细化分析提供理论依据，具有应用价值。