季冻区高铁新型桩板结构体系-路基土体冻胀作用机理及变形特性研究

The pile-plank embankment has been widely adopted in non-frozen regions, showing a good performance in solving the settlement-related problems of high-speed railway subgrades. In order to prevent track structure damage and railroad line irregularity caused by frost heaving of subgrade soils in seasonally frozen regions, the principle investigator of this grant proposed an improved pile-plank embankment system by incorporating a layer of thermal insulation cushion below the concrete plank. Although the feasibility of this new system has been studied in context of Moscow-Kazan high-speed railway design, but there is lack of research on its frost heave deformation mechanisms. To mitigate this gap, this research project performs a series of frost heave tests on subgrade soils under different confinements and frozen soil microstructure analysis, aimed at establishing a unified frost heave stress-strain relation under different low temperature conditions and further revealing the frost heave mechanisms at a micro scale. Through a series of the pullout test of pile element in soils upon frost heave and frost heave model test of newly improved pile-plank embankment，this project investigates the interaction mechanisms between pile-plank system and subgrade soil subjected frost heave and the distribution characteristics of frost heaving force acting on the pile-plank structure. On basis of the principle of structural analysis, this project develops a semi-analytic approach for calculating frost heave deformation of pile-plank structure. Finally, this project proposes a simple numerical model for frost heave deformation analysis of the whole pile-plank embankment by implementing the developed unified frost heave stress-strain relation into a thermo-mechanical coupled finite element code. The outcomes of this research is able to provide a theoretical basis for the design of this new structure and the evaluation of its long-term service performance.

现有桩板结构路基已被广泛应用于非冻土区并成功解决了高铁路基的沉降变形问题，为解决季冻区土体冻胀引起的轨道结构损伤及线路平顺性问题，申请人提出了铺设保温板垫层的新型桩板结构路基，并结合莫-喀高铁的设计完成了该新结构控制冻胀变形的可行性研究。但这一新路基结构形式的冻胀变形机理研究在国内外尚处空白。基于此，本项目拟通过不同约束条件下土体冻胀试验及微观结构分析，建立不同低温条件下土体冻胀应力-冻胀应变的归一化关系并揭示土体冻胀的微观机理；结合桩单元体冻拔试验和桩板结构路基冻胀模型试验，揭示桩板结构体系-冻胀土体的相互作用机理并明确桩板结构体系所受冻胀力的分布特征，进而基于结构力学原理建立桩板结构体系冻胀变形的半解析分析方法；将土体冻胀的归一化关系嵌入热-力耦合有限元理论框架，最终建立桩板结构路基冻胀变形分析的数值计算模型。本研究成果预期为该新结构的设计及长期服役性能的评估提供理论基础。

我国季节冻土区分布广泛，然而关于季节性冻土的研究则相对零碎而不系统全面，且很多机理尚未探明，特别是在铁路线路工程设计中，缺乏广泛认同的设计理论和经验支持。在一些季节性冻土区，已经出现较为严重的铁路路基冻害现象，冬季强烈的冻胀将直接导致轨道结构的损伤、破坏及春季严重的融沉和翻浆。高速铁路对路基工程的平顺性要求极高，如高速铁路设计规范要求无砟轨道路基工后沉降不宜超过15 mm，且冻胀量不超过轨道扣件的调低量4 mm，这给季节性冻土区路基工程的冻胀变形控制提出新的挑战。本课题以季冻区高速铁路为研究对象，提出一种在承台板底部铺设XPS保温板的新型桩板结构路基，并通过现场调研、模型试验、理论分析和数值计算等科研方法对其进行研究分析。通过不同约束下土体冻胀试验，研究路基冻土在不同边界约束条件下的冻胀变形机理；通过整体路基结构的冻胀模型试验，揭示桩板结构体系与土体在冻胀变形情况下的相互作用机理；通过水-热-力耦合有限元计算平台，建立季节性冻土区桩板结构路基冻胀变形的计算理论与预测方法。本课题研究成果已成功应用于莫-喀高铁路基段、川藏铁路桥隧连接过渡段和成渝中线高铁红层泥岩土路堑段等不同地理位置线路的设计方案中，该成果可为解决季节性冻土区高速铁路线路平顺性问题提供理论支撑。