季节冻土区含盐水泥稳定碎石集料侵蚀膨胀的宏细观机理研究

Recently, some High Speed Railway (HSR) in seasonally frozen region experienced a continuous and severe heave, both in the subgrade bed and the cushion layer at the bottom of the subgrade filled with cement treated graded macadam (CTGM), which detrimentally influenced the operation of HSR. The soluble salt content in the aggregate was found to be relatively high, and expansive mineral like thaumasite and ettringite were identified according to mineral composition analysis, both of which were generated as a result of salt attack on cement. Intensive researches were conducted on the salt attacking induced heave of cement treated clay soil with few focus on the CTGM constituting of larger particles and pores. Based on the existing studies, especially the in-situ monitoring and experimental results，the macroscopic and microscopic mechanism of salt attacking induced heave of CTGM will be investigated, and the theoretical deformation model will be established in this project . The critical conditions and influencing factors of the salt attacking induced heave will be analyzed experimentally. X-ray diffraction, scanning electron microscope and computed tomography methods will be adopted to study the microscopic heave mechanism .Finally, the theoretical deformation model will be proposed based on numerical calculation of discrete element method and theoretical analysis of minimum energy method, which will be further verified and modified by comparing with experimental results.

近年来，我国季节冻土区高速铁路部分段落的基床及基底的水泥稳定碎石集料层发生了明显的膨胀变形，严重影响了线路的正常运营。取样分析结果显示，集料中易溶盐含量偏高，且含有硅灰石膏、钙矾石等盐分侵蚀水泥形成的膨胀性矿物。目前，针对水泥改良细粒土盐分侵蚀膨胀的研究已较为成熟，还缺乏针对粗颗粒、大孔隙的水泥稳定碎石集料的膨胀变形研究。本项目基于现有研究成果，特别是现场监测及试验结果，从宏细观尺度出发，采用室内试验、数值模拟与理论分析相结合的方法对含盐水泥稳定碎石集料的侵蚀膨胀变形机理与理论模型进行研究。通过考虑环境变化的室内侵蚀膨胀试验提出宏观变形的发生条件与影响因素；通过成分、矿物及细观结构分析试验（X光衍射、扫描电镜及三维重构分析），研究膨胀的细观发育机制。结合离散元方法及基于最小能量原理的理论分析方法，构建多因素条件下含盐水泥稳定碎石集料侵蚀膨胀的理论模型，并通过对比试验结果进行验证与改进。

在道路与铁道工程中，盐分侵蚀水泥改良填料引起膨胀以及破坏的问题日益显现，本研究基于我国季节冻土区盐分侵蚀无砟轨道路基水泥改良填料引起膨胀变形的问题，通过现场调研、原位测试、室内试验及理论计算分析等手段对侵蚀膨胀变形特性与宏细观机理展开研究，主要开展的研究工作和结论有：.（1）无砟轨道路基侵蚀膨胀变形主要发生在路桥（涵）过渡段范围，整体呈现出波动增长的特性，与温度具有较大的相关性，降温过程中上拱变形增长较快；基床表层及地基垫层由于水泥掺量更多，盐分聚集及外部环境影响剧烈，更易发生侵蚀膨胀；.（2）系统分析了各因素对于侵蚀膨胀变形的影响，侵蚀膨胀量随硫酸钠含量的增加而增加，随水泥掺量的增加，则没有一致性规律；较低的碱性环境下（pH<10）也可能发生侵蚀膨胀。结合全局灵敏度分析方法，各因素对膨胀影响从大到小的排序分别为：硫酸钠含量、养护溶液硫酸钠浓度、压实度、硫酸钙含量、养护湿度、水泥含量及水泥比表面积。.（3）从化学反应角度出发，同时考虑水泥水化，晶体填充，石膏、钙矾石和芒硝晶体的生成，以及反应过程中水分蒸发和水泥固化作用等因素的影响，通过理论计算及实验修正，建立了侵蚀膨胀预测模型。.（4）结合数值分析方法，研究了膨胀过程中颗粒切向刚度、法向刚度及摩擦系数等细观参数对集料宏观变形的影响，同时明确了膨胀过程中，集料内部孔隙、颗粒配位数及能量的演化规律。.研究成果对于季节冻土区道路与铁道工程的设计施工及无砟轨道路基的运营维护有重要的参考价值。