Thermal State of Frozen Ground along National Highway No. 214 from Xi'ning to Yushu on the Northeastern Qinghai-Tibet Plateau, China

The permafrost covers about 330 km along the National Highway No.214 (hereafter the G214), the second longest highway from Qinghai Province into Tibetan Autonomous Region. The hazards of frost heaving and thawing settlement of highway foundations and pavement breakout prevail among the roadway because of thawing of warm and ice-rich permafrost, which is unstable and sensitive to climate changes and anthropogenic activities. Based on analysis of thermal state from extensive field investigations and measurements of ground temperature, the frozen ground along the G214 could be categorized as alpine permafrost zone in the Bayan Har Mountains (APBHM), seasonally frozen ground zone in the valley of the source area of the Yellow River (SFSAYR), and alpine permafrost zone in the Buqing Mountains (APBQM). Based on areal extent (continuity) and ground ice (moisture) content of frozen ground, the design and maintenance principles of the G214 include thawing principle to frozen ground with relative less lower content and shallow active layer, and controlling thawing principle to frozen ground with relative higher ice content.