Design and research of high voltage transmission lines on the Qinghai–Tibet Plateau—A Special Issue on the Permafrost Power Lines

Abstract

The Qinghai–Tibet Power Transmission Line (QTPTL), a project of the ±400kV direct current (DC) grid system from Golmud in Qinghai Province to Lhasa in Tibet Autonomous Region, China, was recently built to meet the power transmission needs. On the Qinghai–Tibet Plateau (QTP), it is another milestone engineering project since the completion of the Qinghai–Tibet Railway in 2006. The project route runs mainly parallel to the railway, passing through permafrost regions in a general north-to-south direction. Different foundation types were used for the QTPTL to cope with the complex permafrost conditions, difficult and demanding construction techniques on the plateau, and warming climate and degrading permafrost. In building the QTPTL, most foundations were embedded in permafrost soils, and the interactive processes between the tower or pile foundation structures and permafrost soils differ significantly in comparison with those of highways and railroads. Great efforts were made by engineers and researchers to economically design and construct the QTPTL. In the design, new types of foundations were developed and adopted to reduce frost heaving and thaw settlement of foundation soils. A long-term monitoring system was installed simultaneously or immediately after the construction to record temperatures, deformations, stresses, and moisture contents of foundation soils at representative sites along the project route. To take into account the thermal, hydrological and mechanical impacts of the backfilled soils on the foundation stability, soil samples from the excavation pits and backfills were taken for testing the physical and mechanical properties of soils in frozen and thawed states. Based on the monitored data, and taking into account various engineering, permafrost, and environmental conditions, the thermal and mechanical properties of foundation soils were meticulously studied and changes in tower foundation stability predicted under climate change scenarios. Environmental impacts from the project construction and operation were also assessed accordingly. This Cold Regions Science and Technology Special Issue on the Permafrost Power Lines summarizes the results of these studies, and it may be beneficial to understanding the interactions between tower foundations and permafrost, to forecasting and evaluating of changes in the stability of the QTPTL, and to providing recommendations for engineering practices in maintaining the operating QTPTL. These results and conclusions may also provide valuable insights and references for the design, construction and operation of power transmission lines in similar permafrost region or similar cold region infrastructures.