Discussions on tower base design principles and geological conditions from Budongquan to Fenghuo mountain in the project of ± 400 KV AC-DC network in Qinghai-Tibet plateau

400 KV AC-DC Network project in Qinghai and Tibet is one of the national key projects, it is located in the highest latitude in the world up to now, and the largest power transmission project. This project has the total line length of 1038 km, and passes through 565km of perennial frozen soil, where construction is a globally technical problem. Budongquan-Fenghuo Mountain frozen soil area is in the hinterland of Qinghai-Tibet plateau. The unhealthy geological features in this area include high temperature, high ice content, perennial frozen soil, thick ground ice, ice picks, frost heave mounds, hot melt lakes and pools. The engineering complexity of perennial frozen soil makes a more serious damage to the project in the respect of frost and thaw damage than other seasonally frozen soil. This paper has analyzed and evaluated many elements in this area: the typography, climate, terrain lithology, geological structure, hydro logical conditions, the distribution of perennial frozen soil, the distribution of the ground temperature, ice content, etc. In addition, this paper also has also proposed the four tower base forms: pile foundation, prefabricated foundation, cone-cylinder foundation and pull "V" stand-alone tower base. All the research results provide adequate solutions to the basic problems in the transmission projects in perennial frozen soil areas and a guarantee to the secure and sustainable operation of the lines.