Figure 17.6
Engineering for permafrost. The Qinghai–Tibet railway, completed in 2006, has the highest elevation of any railway in the world. It is 1,956 km (1,215 mi) long and connects Xining, Qinghai Province, to Lhasa, Tibet Autonomous Region, China. Much of it is built on permafrost. If ice thaws beneath the tracks, the tracks will move, and such movements could derail a high-speed train. As a precaution, the tracks are raised above the permafrost, and in places vertical pipes circulate liquid nitrogen beneath the pilings to keep the soils around them frozen.(© View Stock/Getty Images)