青藏高原多年冻土区路基下融化夹层水热过程观测与模拟研究

According to the tendency of climate warming and generally developing thawed-interlayer under the embankment of the Qinghai-Tibet Highway (QTH) and the Qinghai-Tibet Railway (QTR) in permafrost regions, the observation and simulation study on water-heat process of the thawed-interlayer will be systematically carried out. The project is concentrated on the following aspects: . Based on the data of ground temperature and geological survey from the QTH and QTR, the growing characteristics and the main factors affecting the development of the thawed-interlayer under the embankment of the QTH and QTR would be analyzed, and then two typical scetions of the QTH in which the thawed-interlayer has been developing rapidly, are to be chosen to be monitored, and the sensors used to measure simultaneously water content and ground temperature, would to be placed into the thawed-interlayer as required, the changes of water and heat are to be explained, respctively. By obtaining the data of heat flux beneath the slope toe, the exchange mechanism of heat between soils under the embankment and natural field along the horizontal direction is to be discussed. Based on soil water dynamics, heat transfer theory and frozen soil physics, a numerical coupled model of water-heat in the thawed-interlayer would be set up, the corresponding computer program is done and justified, and checked on the basis of the observed data. Using the model, the evolution tendency of thawing-interlayer in the future is to be predicted and analyzed. The present project will make us know the developing mechanism and evolution of thawed-interlayer under the embankment in permafrost regions more entirely and exactly, which has special theoretical and engineering meanings, and will supply a strong base for forcasting the embankment disease in permafrost regions.

针对青藏高原多年冻土区路基下融化夹层普遍发育的现状，系统开展融化夹层水热过程观测及模拟研究。具体内容包括：充分利用已有青藏公路与青藏铁路沿线的地温及勘察资料，查明两种路基下融化夹层的发育特点及影响融化夹层发育的主要因素；在路基下典型发育融化夹层的路段设观测断面，通过观测融化夹层中的水分及温度状况，揭示出融化夹层水热动态变化过程；通过观测断面不同位置的地温及坡脚下水平方向上的热流观测数据，分析路基下部与天然场地下部土体在水平方向上的热交换机制；基于土壤水动力学、传热学与冻土物理学，建立路基下融化夹层水热过程数值模型，同时编制和调试相应的模型计算程序，并运用观测数据（温度与水分）对模型进行检验和修正，采用得到的数值模型预测和分析路基下融化夹层的演变趋势。本研究对多年冻土区路基下融化夹层的发育机理及演变趋势有更全面准确的认识，具有重要的理论和实际工程意义，可为冻土区路基病害的预测提供基础。

多年冻土区路基下融化夹层是指在季节最大冻结深度和多年冻土上限之间形成的隔年或多年不冻的融化土层。融化夹层的形成与发展往往导致路基出现较大的沉降变形。基于青藏铁路长期监测系统所获取的路基地温与变形资料，以及青藏公路新建观测场地的地温与变形资料，查明融化夹层的发育特点及影响融化夹层发育的主要因素，揭示出融化夹层动态变化过程，建立路基下融化夹层热力过程数值模型，预测和分析路基下融化夹层的演变趋势。项目取得的主要结果如下：(1)揭示了青藏铁路沿线天然场地不同地温分区下的多年冻土变化特征；(2)揭示了青藏铁路沿线主要融区的特征及其变化趋势；(3)总结了青藏铁路多年冻土区路基下融化夹层的分布特征及主要影响因素；(4)阐明路基累计沉降变形与融化夹层厚度之间的关系，揭示出路基下融化夹层厚度增加的主要来源；(5)利用青藏铁路路基长期监测系统的地温监测资料，揭示了路基下融化夹层的形成机制；(6)构建含融化夹层路基热力计算模型，模拟预测了青藏铁路路基修筑后30年的温度场与变形场；(7)证实了块石护坡与热管补强措施治理路基下融化夹层的效果。项目积累了典型路基监测断面近15年较为完整连续的地温与变形资料。本研究加深了对多年冻土区路基下融化夹层的形成机制及变化趋势的认识，具有重要的理论和实际工程意义，可为冻土区路基病害的预测提供科学基础。