Numerical study of long-term cooling effects of thermosyphons around tower footings in permafrost regions along the Qinghai-Tibet Power Transmission Line

Abstract Two-phase closed thermosyphons are extensively used for cooling foundation soils of tower footings in permafrost regions along the Qinghai-Tibet Power Transmission Line (QTPTL). In this paper, the working period of these thermosyphons is firstly determined by field observations. Then, a 3-D numerical heat transfer model is constructed to study the long-term cooling effects of thermosyphons and thermal performance of foundation soils. The numerically simulated results show a significant cooling of foundation soils near thermosyphons in cold season approximately from late October to early May, and a rapid shift of the thermosyphon cooling to the footing side due to greater thermal conductivity of the concrete footing. As a consequence, a colder bulb would develop under the footing, increasing the bearing capacity of foundation soils. In warm season from the mid-May to mid-October, the maximum thaw around the footing would be greater than that in the natural ground due to better heat transfer through the concrete footing. During a 50-year operational period, foundation soils under the footing would roughly go through about four thermal stages under a combined effect of the thermosyphon cooling and climate warming: a rapid cooling stage in the first to 5th year, a stable stage in the 6th–15th year, a rapid warming stage in the 16th–35th year and a slow warming stage after the 35th year. During the operational period, the maximum thaw around the footing would be less than the embedding depth of the footing (5.8 m), meeting the design criterion for thermal stability of foundation soils.

[1]  Liu Yongzhi,et al.  A review of recent frozen soil engineering in permafrost regions along Qinghai‐Tibet Highway, China , 2002 .

[2]  Zhang Jianming,et al.  Monitoring the Tower Foundations in the Permafrost Regions along the Qinghai-Tibet DC Transmission Line from Qinghai Province to Tibetan Autonomous Region , 2012 .

[3]  Yang Pan,et al.  Numerical investigations and engineering applications on freezing expansion of soil restrained two-phase closed thermosyphons , 2002 .

[4]  Qihao Yu,et al.  Impacts of Permafrost Mean Annual Ground Temperature and Ice Content on Thermal Regime of Pile Foundation of Qinghai-Tibet Power Transmission Line , 2012 .

[5]  Qingbai Wu,et al.  Permafrost temperatures and thickness on the Qinghai-Tibet Plateau , 2010 .

[6]  R.A.S. Ratchliffe,et al.  Book reviewBoundary-layer meteorology: A new quarterly journal of physical and biological processes in the atmospheric boundary layer. R. E. Munn (Editor). D. Reidel Publishing Company, Dordrecht, 1969, Volume 1(1). , 1971 .

[7]  Mingyi Zhang,et al.  Seismic Analysis of Embankment of Qinghai–Tibet Railway , 2009 .

[8]  Liu Yongzhi,et al.  Interaction study of permafrost and highway along Qinghai-Xizang Highway , 2003 .

[9]  Wei Zhan-yua.  Analysis the Reason of Subside and Displacement of Cone Cylindrical Foundation for Qinghai-Tibet Railway 110kV Transmission Project and Treatment Measure , 2009 .

[10]  Qihao Yu,et al.  Displacements of tower foundations in permafrost regions along the Qinghai–Tibet Power Transmission Line , 2016 .

[11]  Di Wu,et al.  The thermal budget evaluation of the two-phase closed thermosyphon embankment of the Qinghai–Tibet Highway in permafrost regions , 2014 .

[12]  Zhizhong Sun,et al.  Numerical study on cooling characteristics of two-phase closed thermosyphon embankment in permafrost regions , 2011 .

[13]  Lei Guo,et al.  Analysis of tower foundation stability along the Qinghai–Tibet Power Transmission Line and impact of the route on the permafrost , 2016 .

[14]  Qingbai Wu,et al.  Thermal state of the active layer and permafrost along the Qinghai-Xizang (Tibet) Railway from 2006 to 2010 , 2011 .

[15]  Z. Wen,et al.  Managing ice-rich permafrost exposed during cutting excavation along Qinghai–Tibetan railway: Experiences and implementation , 2011 .

[16]  Ma Wei,et al.  Construction on permafrost foundations: Lessons learned from the Qinghai–Tibet railroad , 2009 .

[17]  Amir Faghri,et al.  Thermal characteristics of a closed thermosyphon under various filling conditions , 2014 .

[18]  Z. Wen,et al.  Remedying embankment thaw settlement in a warm permafrost region with thermosyphons and crushed rock revetment , 2012 .

[19]  W. Ma,et al.  Characteristics and mechanisms of embankment deformation along the Qinghai–Tibet Railway in permafrost regions , 2011 .

[20]  W. Ma,et al.  Monitoring investigation on thermal stability of air-convection crushed-rock embankment , 2010 .

[21]  Zhao Lin,et al.  Thermal regimes and degradation modes of permafrost along the Qinghai-Tibet Highway , 2006 .

[22]  W Zhi,et al.  Analysis on effect of permafrost protection by two-phase closed thermosyphon and insulation jointly in permafrost regions , 2005 .

[23]  S. H. Noie.  Heat transfer characteristics of a two-phase closed thermosyphon , 2005 .

[24]  L. Zhiqiang,et al.  Numerical analysis for cooling effect of open boundary ripped-rock embankment on Qinghai-Tibetan railway , 2006 .

[25]  Yang Yong-ping,et al.  Numerical Analysis of Proper Thermosyphon Inclination Angle Used in Permafrost Embankment , 2006 .

[26]  Pan Wei-dong.  Application of Thermal Probe to Enhance Thermal Stability of Roadbed in Plateau Permafrost Areas , 2003 .

[27]  Chen Wu.  Cooling effect of combined L-shaped thermosyphon,crushed-rock revetment and insulation for high-grade highways in permafrost regions , 2012 .