Problems and countermeasures in construction of transmission line projects in permafrost regions

Construction of power transmission lines is becoming an important part of permafrost engineering in China. This paper reviews the construction status and problems of transmission lines in different countries, as well as corresponding solutions that would be of practical significance for sustainable engineering practices. Russia has the longest history of transmission line construction in permafrost areas, with transmission lines (mainly 220 kV and 500 kV) spanning approximately 100,000 km. However, all countries suffer from permafrost-related tower foundation stability problems caused by freezing- thawing hazards such as frost heave and thaw settlement, frost lifting, and harmful cryogenic phenomena. As point-line transmission line constructions, the lines, poles and towers should be reasonably selected and installed with a comprehensive consideration of frozen soil characteristics to effectively reduce the occurrence of freezing-thawing disasters. Reinforced concrete pile foundations are widely used in the permafrost regions, and construction in winter is also a universal practice. Moreover, facilitating engineering measures like thermosyphons are an effective way to reduce freezing- thawing hazards and to maintain the stability of tower foundations.