行车荷载作用下道砟横向迁移引起道床变形的细观力学分析

Ballast lateral movement induced by moving train load leads to track deformation and consequently give rise to security risk of train operation. Contact force between ballast grains induced by train load is the driven force of ballast lateral movement. Track deformation characteristics concluded by current researches based on triaxial test and model test have not directly taken the contact force between ballast grains into account. Therefore, they are insufficient to evaluate the deformation stability of ballasted track effectively and consequently affect the treatment strategy and maintenance cost. This program is proposed to investigate the inter-particle contact force evolution, spatial topology characteristics of force chain and ballast displacement in the lateral layered ballast-roadbed system by considering the contact force propagation characteristics in granular materials and interaction between ballasted track and roadbed. Both macro and micro mechanical analysis are adopted. Then the relationship between inter-particle contact force and ballast displacement can be built to illustrate the force transfer mechanism that vertical train load can result in lateral displacement of ballast. The relationship between ballast displacement and strain can also be built by averaging. Finally, track deformation can be linked with inter-particle contact force through ballast displacement, which makes the deformation characteristics more rational under cyclic loads. The research achievements will offer a scientific criterion to track deformation control and other related maintenance.

行车荷载作用下道砟颗粒会发生横向迁移，进而引起碎石道床变形，危及行车安全。道砟颗粒横向迁移的驱动力是行车荷载引起的道砟颗粒间的接触力。目前基于单元体试验和模型试验研究得到的碎石道床变形特性,并未直接考虑道砟颗粒间接触力对道床变形的影响，从而在评价道床变形稳定性时具有一定局限性，进而影响到道床的整修策略和维养成本。本项目以碎石道床—基床层状散体为研究对象，考虑散体中接触力传递特性和层面相互作用，采用宏细观相结合的方法，对行车荷载作用下道砟颗粒间接触演化、力链空间拓扑及道砟位移场等进行分析，得出道砟颗粒间接触力与颗粒位移的对应关系，以明确垂向荷载引起道砟横向迁移的传力机制，并基于平均化方法关联道砟颗粒位移与道床变形。最后以道砟颗粒位移为中间量，建立碎石道床散体系统细观接触特征（包括力链）与宏观变形的关系，从而更为合理地确定行车荷载引起的道床变形及其稳定性，为道床变形控制等维养工作提供科学依据。

有砟铁路碎石道床的动力特性不仅决定了线路的行车速度和轴重，还直接关系到行车安全和维养成本。现有研究对道砟的运动、迁移特性及其引起的道床结构演变考虑不足，这不利于评价道床的变形稳定性。为此，本项目以碎石道床层状颗粒体系为研究对象，采用室内和数值模型试验相结合的方法开展宏-细观的量测和分析，系统研究了“轮轨力-道床内力-道砟颗粒运动-道床变形”的动力响应过程，明确了速度、轴重变化对道床的荷载传递和扩散性能、道砟颗粒的受力及空间运动特性、道床累积塑性变形及动刚度的影响，得到如下创新性结论：（1）获得了横向不同位置道砟所受平均应力、偏应力与轮轨力的量化关系，发现碎石道床横向和纵向扩散荷载的能力随轮轨力的增大有所下降，是垂向累积塑性变形呈幂律增大的力学根源；（2）道砟颗粒在水平面内的转动主要表现为累积转角变化，而其他两个平面内的转动主要表现为可恢复转角，这一特性不受轮轨力、频率和加载次数的影响；行车荷载作用下道砟颗粒水平面内的旋转和竖平面内的滚动是其横向迁移的主要形式，而道砟颗粒的横向平动不明显；（3）轮轨力变化对道砟颗粒的加速度和转动均有显著影响；而加载频率仅对颗粒加速度影响较大；轮轨力和频率在影响颗粒接触力和运动时存在相互增益，高频作用下颗粒的加速度对轮轨力的变化更敏感；（4）发现道砟颗粒间动接触力因颗粒转动表现出“跷跷板”效应，通过获取同相和反相接触应力的概率分布，提出了基于区域平均应力估算颗粒间最大接触应力的方法。此次研究将以往侧重外部宏观现象的“轮轨力-道床变形”关联分析，扩展为内外部特征兼具、宏细观响应并存的“轮轨力-道床内力-道砟颗粒运动-道床变形”全过程分析，提出了通过约束道砟迁移来减小道床变形加固措施。研究结果可为高速、重载条件下碎石道床的设计和维养提供理论基础。