Frost Jacking Characteristics of Transmission Tower Pile Foundations with and without Thermosyphons in Permafrost Regions of Qinghai-Tibet Plateau

Frost jacking of electricity transmission tower (ETT) pile foundations in permafrost regions of the Qinghai-Tibet Plateau is becoming increasingly serious. This study investigated the effects of thermosyphons on the frost jacking characteristics of such pile foundations. Field tests of pile foundations with and without thermosyphons were carried out in the Wonkhu-Budongquan section of the Qinghai-Tibet Plateau. A three-dimensional finite-element model was established to analyze the effectiveness of thermosyphons, ground temperature distributions, and jacking displacements and force characteristics of ETT pile foundations. The results showed that the power of thermosyphons decreases yearly within 30 years. The thermosyphons can effectively increase the cold reserves of the permafrost and reduce the soil temperature; the soil temperature around the pile and the depth of thaw is the lowest in the fifth year, and this will increase the top of permafrost by 48 cm in the thirtieth year. Thermosyphons can effectively increase the adfreezing force of the pile side below the active layer and reduce the frost jacking displacement, thus alleviating frost jacking damage to ETT pile foundations.