工程扰动和气候变暖双重情景下高温多年冻土区铁路路基的热-力强化机制研究

Excessive or differential settlement appears in quiet a few railway embankments in warmer permafrost regions. How to strengthen these embankments is a significant matter that world confronted. Under the background of global warming, whether the strengthening measures could effectively cool the embankment in a short term and enhance the thermal-mechanical stability of the embankment with engineering disturbance in a long term is the key issue. On the basis of conventional three-dimensional turbulence model considering air temperature and wind speed, an improved Xiyuan model considering accelerated creep of frozen soil will be introduced. The two yield-surface rheological yield function and the critical boundary discriminant function for accelerated creep will be introduced. A three-dimensional coupled thermal-mechanical model and forward and back analysis method will be applied to reveal the thermal-mechanical stability responsing process and failure mechanism of the noremal reinforcement measures in road engineering in permafrost regions. Some new strengthening measures will be promoted based on the coupled model on the joint effect of global warming and engineering disturbance. Differential strengthening mechanism on sunny and shady slope will be proposed through the three-dimensional numerical experimentation. Achievement of this project will provide science-technology support for safe operation of the existing road engineering in permafrost regions.

不少高温多年冻土路段铁路路基在服役期间出现了过量、不均匀沉降的问题，如何针对这些路基进行强化是各国面临的重要问题。在气候变暖的背景下，强化措施能否在短期内对热扰动后的冻土路基行成有效降温、长期提高路基热-力稳定性是该项研究的主要瓶颈。本课题拟以青藏铁路多年冻土区实体工程为例，基于现场调研、现场原位监测、室内试验，在考虑空气中温度、风速的三维湍流模型基础上，引入考虑冻土加速蠕变的改进西原模型、帽子型双屈服面屈服函数、冻土加速蠕变界限判别函数，构建三维湍流-热-力耦合正反分析模型，揭示多年冻土区道路工程中目前常用强化措施的热力稳定性响应过程和失效机制；在考虑气候变暖、工程热扰动的双重情景下提出新型强化措施；通过三维数值试验来得出不同路基的阴阳坡差异性强化机制。课题成果为多年冻土区已有道路工程的安全运营进一步提供科学支撑和技术保障。

建设于多年冻土区的铁路路基无论在建设过程中还是运营过程中，都可能会在先期工程扰动和后期气候变暖的影响下逐步出现各类病害，给工程设计、施工、后期维修补强带来了十分严峻的考验。课题组首先基于青藏铁路北麓河高含冰量试验段现场监测资料分析了传统方式布设的块/碎石护坡、热管作为强化措施在高温、低温多年冻土区不同路段的强化效果及机理，结果表明：高温多年冻土区铁路路基阴阳坡差异性退化现象十分普遍，块/碎石护坡除在高温高含冰量多年冻土区路基阳坡并不足以限制先期工程热扰动下多年冻土地基的退化，其他工况下强化效果尚可。碎石护坡+热管的强化效果除在路桥过渡段墩台附近强化效应不足外，其他路段强化效果较为理想。以“冷却路基”为主导思想的强化措施及时施加仍能有效限制高温多年冻土路基的沉降变形。其次，通过实体建模方式建立的气固分离的块石路基模型和基于局部非热平衡理论建立的块石路基模型的计算和分析结果均表明，块石层内部局部非热平衡现象较为普遍，将来该方面数值计算过程中应考虑这一因素的影响。此外，通过改进建模方式，融入强度折减法和冻融界面力学发展了块石路基稳定性的计算方法，未来可基于此对工程扰动和气候变暖双重情境下的多年冻土路基的热-力稳定性进行系统评估和筛查。在考虑气候变暖、工程热扰动的双重情景下提出新型强化措施，并进一步通过三维数值试验分析并阐明了应对高温多年冻土路基阴阳坡差异性退化的强化机制。研究成果可为未来多年冻区铁路路基的补强工程的设计和施工提供科学依据。