热管性能劣化机制及其对冻土区输电塔基稳定性影响研究

Thermosyphons are common engineering measures used for efficiently cooling foundation soils in permafrost regions. The damage or corrosion of the pipe, or decomposition of working fluid may result in a lowering effectiveness of a thermosyphon, or even its failure. However, the fining study on the deterioration mechanism, effectiveness assessment, as well as its influence on the variation of stability of foundation soils is still insufficient. More than 7000 thermosyphons were used for cooling foundation soils along the Qinghai-Tibet direct current power transmission line (QTDC), revealing the general close relationship between the stability of the line and the performance of the thermosyphons. Based on the results of the examination on the working states of thermosyphons, aiming to reveal the deterioration mechanism and its influencing factors of thermosyphons, correlation analysis will be conducted between the working states of thermosyphons and the distribution of climate, frozen soil, engineering conditions of thermosyphons along the QTDC. To give an assessment method about the cooling efficiency of thermosyphons, the change characteristics with time and space of the pipe wall thermal characteristics will be systematically analyzed based on monitoring data. Besides, the influence of the degree, time, number and location of the deterioration of thermosyphons on the hydro-thermal regime of foundation soils under various permafrost, engineering and climate condition will be quantitatively analyzed by a combination of in-situ monitoring and numerical simulation. The change characteristics of stability of tower foundations under the influence of deterioration of thermosyphons will also be studied. The results of this study are considered to help to improve the assessment of application results of thermosyphons, the prevention and treatment of the deterioration of thermosyphons, and the maintaining of permafrost foundations.

热管是冻土区工程建设中广泛采用的一种地基温度场调控措施，其优点是可快速有效降低冻土地温进而改善地基土稳定性。但在多年冻土区恶劣环境下，管内工质分解等可能引起热管劣化乃至失效，而对其劣化机制、功效评估及其带来的冻土地基稳定性状况变化一直缺乏精细化研究。青藏直流输电线塔地基普遍采用了热管降温保护措施，全线共采用7000多根，因此线路基础整体稳定性与热管功效关系密切。本项目拟以输电塔基及周围热管为研究对象，基于现场检测数据分析热管工作性能与环境及工程因素的相关性，揭示热管的劣化机制与影响因素；基于实例监测，系统分析管壁热参数的时空变化特性，提出热管功效评价方法；通过现场监测与数值模拟，定量研究热管性能劣化程度、时段、数量、位置等对地基土水热状况的影响，分析热管劣化过程中冻土区电塔基础稳定性的变化特性。研究结果有望为热管长期服役性能评估、性能劣化防治与补救，以及冻土地基稳定性维护等提供有益借鉴。

热管是冻土区工程建设中广泛采用的一种地基调控设备，是可快速降低冻土地温、改善地基土稳定性。但热管性能劣化劣化乃至失效特性、及其引起的冻土地基稳定性状况变化一直缺乏精细化研究。青藏直流联网工程冻土基础采用了7000多根热管，这些热管对于塔基的安全稳定具有重要的保障作用，因此线路基础整体稳定性与热管功效关系密切。本项目基于现场监测资料首先揭示了热管性能劣化、尤其是热管失效状况下冷凝段管壁温度变化特性，构建了热管效能识别模式；结合塔基变形观测资料和数值模拟计算，采用热阻法模拟了热管对周围土体地温场的影响，基于现场监测资料验证了计算模型的准确性，揭示了正常热管周围地温场的变化特性，阐明了热管效能降低对其降温效能的影响，明确了热管失效会引起周围地温场的快速升高特性；发现了热管失效可能引起塔基差异变形显著增大、稳定性下降的现象；基于塔基-冻土-热管耦合的三维数值模拟计算，揭示了多年冻土融区热管对塔基的作用效果，阐明了热管引起该区域基础冻拔、以及热管失效引起塔基差异变形显著增大的机理；基于高密度电法现场探测，发现热管的降温作用引起基础周围一定范围内土体的冻结，导致土体电阻率至少升高1个数量级，明确了热管失效引起的基础周围冻土地温升高的现象。基于本项目热管效能识别模式的研究，成功研发了适用于输电线路热管大规模检测的热管检测仪，并对青藏直流联网工程1200根热管的工作状况进行了检测，取得了很好的检测效果，目前“热管检测仪研发及应用”有望获得相关单位的进一步支持，用于对热管检测仪进行规模化生产和商业化推广，并对青藏直流联网工程热管进行全面检测。对热管失效的工程影响的研究，有助于推动冻土工程应用中关于热管失效问题的工程稳定性影响评价、应对措施等方面的研究。