Investigation of an icing near a tower foundation along the Qinghai-Tibet Power Transmission Line

摘要

Formation of ground icings is generally groundwater-related, and ground icings can occur naturally or under anthropogenic influences, or a combination. The evaluative study for the relevant problems of ground icings is important for the design, construction and maintenance of engineering projects in regions affected by ground freezing. Construction of the Qinghai-Tibet Power Transmission Line (QTPTL) was completed in September, 2011. A secondary ground icing was founded near one of the tower foundations in the Tuotuo'he Riverside section in the followed winter. The genesis and formation process of the icing were investigated, using the combined methods of electrical resistivity tomography (ERT), drilling, and ground temperature monitoring. The tower foundation is located on the first river terrace of the Tuotuohe River. The ice-rich, very warm (about -0.05 degrees C) and thin (about 5 m) permafrost and the sub-permafrost groundwater were identified. These conditions are conducive to the growth of ground icing. The embedment of the pile foundations for the QTPTL and the ensued connection of the sub-permafrost water with surface waters are the major causes of the icing. In the subsequent freeze-thawing processes, due to cooling by thermosyphons installed very close to the tower foundation, the ground refreezing prevented the discharge of the sub-permafrost water. The hydrodynamics related to the ground icing growth impacted most of the area with embedded piles, which may influence the adfreezing force, frictional force and tower foundation stability. In the context of climate warming, secondary ground icings may become more hazardous to the permafrost power line. Freezing the soil around the tower foundation or lowering the groundwater table may be effective methods for mitigating the re-occurrence of ground icing. Future work should monitor the pressure, flow and geochemical characteristics of subpermafrost water, by which more proofs will be provided for studying the occurrence and growth of ground icings. (C) 2015 Elsevier B.V. All rights reserved.