高温不稳定多年冻土地区高等级公路路基的适应性研究

The construction of expressway subgrade in warm-instable permafrost region disturbed the original heat exchange conditions between the ground and atmosphere, and different subgrade slope, pavement materials as well as subgrade fillings will generate heat input to accelerate degeneration of underlying permafrost. Thus, the mutual influences between engineering thermal stability of subgrade and permafrost environment need to be emphasized. Whether the monitoring data obtained could provide early warning and effective measures for disease may appear on the subgrade or not, has been a significant matter that researchers confronted. Firstly, based on the monitoring data of standard meteorological system from Qinghai permafrost base, combined with the climate change and local factors, the response of instable-warm permafrost to climate change and engineering thermal disturbance will be analyzed to predict the frozen soil evolution trend. Secondly, the variations of temperature, radiation and heat flux of fine grained soil, coarse grained soil obtained from eight trustum of a pyramid will be used to explain the slope effect on subgrade and establish sunny-shady slope radiation mechanism. The pavement materials and subgrade fillings will also be considered as factors to provide theoretical basis for reasonable selection of subgrade filling types and pavement structures with its influence on the underlying permafrost degradation. Finally, the field measured data will be used to correct and optimize multi-field coupling calculation model, which could be applied to optimize subgrade structure and key parameters. The results of this study would be expected to provide important data and technical supports for the safely operation of highway and improve theory of subgrade construction in permafrost region.

高温不稳定多年冻土地区的高等级公路路基建设破坏了原始冻土环境的地气热交换平衡状态，而且不同的路基坡向、路面材料和路基填料都会产生不同程度的热输入，导致路基下伏多年冻土不断退化。因此，高等级路基本身的工程热稳定性和与冻土环境间的相互影响需要继续关注和维护，获取的监测数据能否对已建道路工程可能出现的路基病害提供预警也是当前面临的重要问题。本课题拟结合气候变化驱动背景，分析高温不稳定冻土对气候变化和工程热扰动的响应；分析路基坡向、路面材料和路基填料对下伏多年冻土退化的影响，建立工程措施、冻土环境与冻土条件相互作用体系，评价其效果及有效性，为合理选择路基走向、填料类型和路面结构型式提供理论依据；利用现有现场实测资料修正和优化多年冻土路基水热多场耦合计算模型，从而优化路基结构及关键参数。通过以上研究，以期为高温不稳定多年冻土区高等级公路工程安全运营进一步提供数据支撑和技术保障。

高温不稳定多年冻土地区的公路路基建设破坏了原始冻土环境的地气热交换平衡状态，而且运营期间不同的路基坡向、路面材料和路基填料都会产生不同程度的热输入，导致路基下伏多年冻土不断退化。项目通过现场调研和数据及理论分析、数值模拟等技术手段，发现多年冻土地区高等级公路病害主要以沉降变形和裂缝为主，出现路基变形的有52段，单幅累计长50.331km，占多年冻土段的11.05%，其中变形较大的区段14.565km，占多年冻土段的3.2%。根据多年冻土区路基变形段所处的区域来看，高温高含冰量多年冻土融化是导致病害的主要原因；分析八棱台、地气热交换等实验系统地温长期时空变化规律，坡向、路面及填料等不同组合对路基活动层的冻融循环过程的影响，发现东-西坡向表面温差最小，坡向热效应最不明显，南北坡向表面温差最大，坡向效应最显著。东南-西北坡向表面温差略低于西南-东北坡向表面温差，它们介于中间。比较的结果建议多年冻土公路路基走向应以南北走向为主，其次可选择西南-东北走向，避免东西走向，以减小坡向效应引起的不均匀沉陷；发现不管是沥青混凝土路面还是水泥混凝土路面，普通路基冻土上限均处于下降阶段，而片块石层的存在可以大幅度抬升或减缓冻土上限下降。路面类型的改变并未明显改变普通路基阴阳坡路肩冻土上限下降幅度，而在浅色水泥混凝土路面片块石路基阴坡路肩冻土上限抬升幅度大于黑色沥青混凝土路面，阳坡路肩冻土上限下降幅度小于黑色沥青混凝土路面，表明浅色路面材料更有利于维持片块石路基的热稳定性。修正和优化水热力耦合作用下冻土工程数值计算模型，并以热棒、块石等主动冷却措施后特殊结构路基为主，分析工程扰动后多年冻土高等级公路路基的工程适应性，研究了斜插式双热棒路基、倒T型块石层宽幅路基结构及块石层+竖向通风管宽幅路基等优化路基结构的长期降温效果。相关结果可以为高温不稳定多年冻土公路工程的安全运营进一步提供数据支撑和技术保障，完善冻土区路基工程建设理论与技术。