考虑覆盖效应的路基水热传输及冻胀过程多场耦合分析模型及方法研究

There are a vast area of seasonally frozen soil in China. Frost heave and thawing settlement of seasonally frozen soil may cause unacceptable damage to the engineering facilities constructed thereon. This is especially true for highways and high speed railways, constructed in a large scale nowadays in China, as they are quite susceptible to foundation deformation. Most of the current research concentrates on the freezing process and possible frost heave for soil which is fully or partly saturated with water. This cannot explain the significant frost heave noted in northwest China where it is dry and lack of rain. Recently the discovery of the Canopy Effect in road foundation and the development of theory for multi-field coupled analysis have offered possibility for a systematic in-depth study of this problem. This research project proposed intends to perform in-depth quantitative analysis of water-heat transfer and froze damage in railway embankment by using the water-vapor-heat-force coupled analysis theory combined with indoor experiments and in-situ measurements, so as to provide scientific support for the prevention and mitigation of frost damage for the road foundation. This is believed to be meaningful for the relevant theory development as well as for the engineering practice.

我国有大面积的季节性冻土区，土的冻融对建于其上的工程设施可造成不可接受的严重危害，特别是对近年来大量兴建、对路基变形敏感的高速铁路和高速公路。目前已有研究多集中于含水土层的冻结过程以及可能发生的冻胀变形，这难以解释西北干旱少雨地区某些铁路和公路路基所发生的严重冻胀变形。近年来路基土体“锅盖”效应（覆盖效应）的发现以及多场耦合分析理论的发展，为该问题的进一步深入系统研究提供了可能。本项目拟在已有工作的基础上，针对路基冻害问题，发展基于水-气-热-力多场耦合分析理论的计算模型和方法，结合试验实测，深入定量分析研究铁路路堤内水热传输和发生冻害的规律，从而为制定有效可行的路基冻害防治措施提供科学依据。相信该项研究在有关基础理论及工程实践方面均有重要意义。

针对西北干旱地区铁路路基在冬季同样会发生冻胀的问题，提出时变覆盖效应的概念，即路基浅层含有一定水分的细粒土在入冬时节逐步冻结，对在温度梯度作用下向上迁移的深层水气形成逐渐加强的覆盖作用，从而使水分在路基顶层之下集聚结冰，引发较大的冻胀。进而通过在兰新铁路武威段历年冻胀较大区段选取监测断面，在路基中心与路肩部位不同深度布设温湿度传感器及冻胀计等，进行细致的持续监测，取得宝贵的实测数据。还与有关厂家合作研制了水-热-力边界条件可变可控的时变覆盖效应冻融循环模拟试验仪，可以实现复杂时变覆盖效应的模拟，为深入开展有关研究提供了试验工具。结合实测试验及深入的理论分析，进一步改进发展了考虑非饱和土中水气迁移、热传导、相转换的多场耦合理论，特别是根据实测分析在模型中考虑了冻结缘中以前被忽略的冰-水-气非饱和层的存在，还据已有研究通过解析分析确定铁路道砟层存在条件下路基顶面的水气蒸发条件，较好实现了此类问题的数值模拟。通过理论分析、数值模拟结合实测试验论证了时变覆盖效应是西北寒旱地区铁路路基发生较大冻胀的重要原因，并分析了主要有关因素的影响，深入揭示了该地区路基冻胀机理，可为此类路基冻害防治提供参考。部分成果已在国内外发表或在申请有关专利，对相应领域的理论发展及技术进步起到一定的促进作用。