干湿交替与流固相变下高铁基床填料累积变形演化规律及细观机理

Investigation of China’s operating high-speed railway indicates that the scope and rick of subgrade bed disease obviously increases in very moist and cold region. The basic reason lies on that the mechanical properties of the fillings are more likely to degrade in complicated water and temperature environment. However, systematic study has not been conducted yet to solve this problem. Therefore, dynamic triaxial test system for coarse-grained soil is remoulded to realize synchronized regulation and control of water content and temperature. The developing law of accumulative deformation and degradative effect for subgrade bed filling is studied in terms of the coupling effect of cyclic loading and alternation of drying and wetting, as well as the coupling effect of cyclic loading and transformation of fluid and solid phase induced by alternation of drying-cooling and wetting-warming. Furthermore, discrete element simulation method is adopted to investigate the influencing mechanism of skeleton particle, fine grain content, water content and temperature on the degradation of the filling. Then microscopic influencing mechanism of alternation of drying and wetting, together with transformation of fluid and solid phase, on the evolution characteristic of accumulation deformation is revealed. For the subgrade bed filling with different granular composition and fine grain content, fabric features of coarse-grained soil is analyzed in terms of particle contact and void distribution. The internal relationship between fabric features and evolution of accumulative deformation is further studied. As a result, the regulation and control method for microscopic fabric is established on a basis of macroscopic mechanical behavior. Finally, given the constructions of Djakarta-Bandung high speed railway in Indonesia and Moscow-Kazan high speed railway in Russia, which are the representatives of going out of China’s high-speed railway, control countermeasures and key parameters are put forward for high-speed railway constructed in rainy and cold regions. Model test is carefully performed to verify the reasonability of new structure and guideposts system.

我国运营高铁调查表明，特别潮湿和寒冷地区基床病害发生范围和风险明显增加，其根本原因在于复杂水温环境下的填料性质更易劣化，但目前这一问题并未得到系统性研究。通过改造可实现湿度和温度同步调控的粗粒土动三轴试验系统，研究循环荷载与“干湿交替”或“干冷-湿热流固相变”耦合下基床填料累积变形演化规律及劣化效应；采用离散元模拟技术，结合三轴试验结果，探明粗粒土中的骨架颗粒、填充细粒料、水分和温度变化等因素对填料劣化的作用机制及规律，揭示水的干-湿交替与流-固循环相变对累积变形演化的细观影响机理；针对级配和细粒含量不同的高铁基床填料，从颗粒接触和孔隙分布两方面分析粗粒土组构特征及其与累积变形演化的内在关系，建立基于宏观力学行为的细观组构调控方法；最后，以我国高铁“走出去”极具代表性的印尼雅万、俄罗斯莫喀高铁设计建造为背景，提出适用于多雨、严寒地区高速铁路基床填料控制对策及关键参数，并进行模型试验验证。

在我国潮湿和寒冷地区，高速铁路基床结构病害的程度和范围明显增加。复杂的水和温度环境下，填料的力学性能更易发生劣化。目前针对此类问题尚缺乏系统性研究。项目改造了一套可实现湿度和温度同步调控的粗粒土动三轴试验系统，研究了循环荷载与“干湿交替”或“干冷-湿热流固相变”耦合下基床填料累积变形演化规律及劣化效应；采用离散元仿真，探明了粗粒土中的骨架颗粒、填充细粒料、水分和温度变化等因素对填料劣化的作用机制，揭示了水的干-湿交替与流-固循环相变对累积变形演化的细观影响机理；针对不同级配和细粒含量的高铁基床填料，基于颗粒接触和孔隙分布分析了粗粒土组构特征及与累积变形演化的内在关系，建立了基于宏观力学行为的细观组构调控方法；以印尼雅万和俄罗斯莫喀高铁为技术背景，提出适用于多雨、严寒地区高速铁路基床填料控制对策及关键参数，并进行模型试验验证。研究表明：高速铁路路基级配碎石颗粒形态对宏观力学性质具有显著影响，不同粒组碎石颗粒的形状、棱角、纹理指标基本呈正态分布特征，随粒径增大，块状颗粒占比提高，棱角和纹理特征愈加突出。低温环境下，无沥青混凝土的普通基床循环变形为高温环境下循环变形的74%，层厚8 cm的沥青混凝土基床循环变形为高温环境下循环变形的75%，层厚12 cm的沥青混凝土基床循环变形为高温环境下循环变形的59%，基床填料在低温冻结下刚度有较大的提升，有效降低基床循环变形。经沥青混凝土层强化后的基床抵抗瞬时、永久变形能力提升显著。相比常用的级配碎石型基床结构，在三类极端温度环境下，沥青混凝土基床顶面的弹性变形均降低40%左右，累积变形发展则更加平缓，趋于稳定后变形减小约23%~59%。高速铁路路基面应力沿横向分布基本均匀，宽度与底座相等；纵向分布呈两类基本形态，结构连续位置为等腰梯形，底座缝位置为等腰三角形。研究成果有助于支撑中国高铁“走出去”战略。