Laboratory testing on heat transfer of frozen soil blocks used as backfills of pile foundation in permafrost along Qinghai-Tibet electrical transmission line
- 355 Downloads
Generally, construction for pile foundation in permafrost has to be carried out in winter to minimize the thermal distribution to the underlying or surrounding permafrost. Thus, there exists a problem that it is hard to meet the stipulated requirement to the compaction degree of the backfilled frozen soil blocks around the pile foundation excavated quickly. In order to study the effect of froze soil blocks on the heat transfer process between pile and permafrost during the construction of the Qinghai-Tibet electrical transmission line in winter, some laboratory tests were carried out for the highly porous frozen soil blocks and the naturally compacted thawed soil body, respectively. In addition, the thermal conductivities were calculated under different temperature gradient according to the measured thermal data. Results show that the convective heat transfer occurs in the highly porous frozen soil blocks at negative temperature corresponding to winter time, which is favorable for refreezing the pile foundation and lowering permafrost temperature. However, backfilling the highly porous frozen soil blocks hardly meet the requirement of compaction degree. It has dual effect on the stability of tower foundation depending on the specific site conditions such as permafrost temperature, ice content, soil type, permeability, hydraulic condition, and embedded depth of pile. Results also show that the equivalent thermal conductivity of the frozen soil blocks is over five times more than that of the thawed soil body on average. This is because the convective heat transfer occurs in frozen soil blocks in winter, which has stronger heat exchange effectiveness and can diminish refreezing time. Tests have revealed the process of heat transfer of frozen soil blocks used as fills around the pile foundation in permafrost, verified its thermal semiconductor effect, and accumulated and expanded data of the thermal conductivity.
KeywordsQinghai-Tibet electrical transmission line Permafrost Thermal conductivity Pile foundation Porous media Freeze-thaw
This work was supported by the Program for Innovative Research Group of Natural Science Foundation of China (No. 41121061), National Key Basic Research Program of China (973 Program) (No. 2012CB026106), Science and Technology Project of State Grid Corporation of China (SGJSJS (2010) 935-936), National Natural Science Foundation of China (Nos. 41171055, 41023003), Funds of the State Key Laboratory of Frozen Soils Engineering of CAS (Nos. SKLFSE-ZY-11 and SKLFSE-ZT-16), and Western Communications Construction Scientific and Technological Project (200831800025). The authors would like to express gratitude to the editor and reviewers for their constructive and valuable comments.
- Cheng Y, Lu X, Liu H, Wang R (2004) Moedl test study on pile foundation of 110 kV transmission line of Qinghai-Tibet railway in frozen soils. Chin J Rock Mech Eng 23:4378–4382Google Scholar
- Lu X, Tong R (2011) Compressive performance test of precast concrete assembly foundation for Qinghai-Tibet AC/DC grid interconnection project. Electr Power Constr 32:16–20Google Scholar
- Lu X, Cheng Y, Fei X, Man G, Guo Y, Xu B (2004) Field tests on mechanical characteristics of permafrost along Tianshan section of Huangji 220 kV transmission line. Chin J Rock Mech Eng 23:4383–4387Google Scholar
- Lyazgin AL, Lyashenko VS, Ostroborodov SV et al (2004) Experience in the prevention of frost heave of pile foundation of transmission towers under northern conditions. Power Technol Eng 38:124–126Google Scholar
- Qian J, Liu H, Yu Q, Cheng D, Zhang J (2008) Stability fuzzy evaluation on typical permafrost territory of Qinghai-Tibet 500 kV electric transmission line. Sci Technol Eng 20:5558–5562Google Scholar
- Qian J, Yu Q, Jiang Z, Gu W, You Y (2011) Experiment on conective and cooling process of macrovoid hollow concrete brick layer. China J Highw Transp 24:8–15Google Scholar
- Reinart I (1969) Design of foundations for the Nelson river transmission line. Paper presented at the Engineering Institute of Canada Annual Meeting. 9–13 Sept. 1969, Vancouver, B.CGoogle Scholar
- Wyman GE (2009) Transmission line construction in Sub-Arctic Alaska case study: “Golden Valley Electric Association’s 230kV Northern Intertie”. Electrical Transmission and Substation Structures Conference 2009 ASCE. U.S.A. 329–341ppGoogle Scholar
- Xu X, Yu L, Wang L (2010) Research on the stability of thermosyphon pile foundations for high-Voltage transmission towers located in permafrost regions. J China Univ Min Technol 39:20–25Google Scholar
- Yu Q, Liu H, Qian J, Fan C, Li D, Xu X (2009) Research on frozen engneering of Qinghai-Tibet 500 kV DC power transmission line. Chin J Eng Geophys 6:806–812Google Scholar
- Zhang J (2004) Study on roadbed stability in permafrost regions on Qinghai-Tibetan Plateau and classification of permafrost in highway engineering. Graduate University of Chinese Academy of SciencesGoogle Scholar