Abstract During the construction of the ±400 kV direct current power transmission line (DCPTL), frozen blocks were backfilled into the foundation pits in permafrost regions because of the lack of backfilling materials and other problems, but this resulted in less compact backfilled soils. To ensure the stability of the tower foundations, a large number of thermosiphons were installed. This study discusses the threat to the stability of tower foundations of water infiltration along the large voids created within the backfilled soils by the use of frozen blocks, and quantifies the efficacy of a combination of thermosiphons and vegetation cover in enhancing tower stability, based on field collected data from January 2011 to April 2017. The results indicate that the cooling effects of thermosiphons caused a large amount of net heat removal from the foundation soils, even during the first operational year of the foundation, while foundation soils without thermosiphons exhibited net heat input during the same period. Ponding in the pits and downward infiltration of water obviously work to warm the foundation soils, and can result in the settlement of the tower footings, threatening the tower stability. The combination of thermosiphons and vegetation cover is shown to effectively cool the foundation soils and to reduce the settlement of the footings, thus ensuring the continued tower stability. This study also shows that the backfilling of frozen blocks should be avoided in the current climate conditions, even though effective cooling measures like thermosiphons are used because the downward infiltration of water along the large voids between the frozen backfilled blocks can’t be totally prevented. If the current degradation of the frozen state of the backfilled soils continues, the infiltrated water, which has been frozen at the bottom of the backfill, will begin to thaw again, threatening the stability of the tower foundations.

中文翻译：

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青藏高原热虹吸和植被覆盖多年冻土输电塔基础稳定性分析

摘要 在±400 kV直流输电线路（DCPTL）建设过程中，由于回填材料不足等问题，冻土块回填到多年冻土地区的基坑中，导致回填土的密实度较低。为了确保塔基础的稳定性，安装了大量的热虹吸管。本研究讨论了通过使用冻结块在回填土壤中产生的大空隙渗水对塔基础稳定性的威胁，并量化了热虹吸管和植被覆盖的组合在增强塔稳定性方面的功效，基于现场收集了 2011 年 1 月至 2017 年 4 月的数据。结果表明，即使在基础运行的第一年，热虹吸管的冷却效应导致地基土壤中大量净热去除，而没有热虹吸管的地基土壤在同一时期表现出净热输入。坑内蓄水和向下渗水明显使地基土变暖，并可能导致塔基沉降，威胁塔的稳定性。热虹吸管和植被覆盖的组合被证明可以有效地冷却地基土壤并减少地基沉降，从而确保塔的持续稳定性。这项研究还表明，在目前的气候条件下，应避免回填冻结块，即使使用了热虹吸等有效的冷却措施，因为无法完全阻止水沿着冻结回填块之间的大空隙向下渗透。如果目前回填土冻结状态的恶化继续下去，已经冻结在回填土底部的渗透水将再次开始解冻，威胁塔基的稳定性。