永久冻土,在我国北部的大兴安岭山区的存在是普遍的。该区的地理高程虽在我国平均雪线之下,海拔七百多米,纬度在45°以北,年平均气温-2℃,地温-3℃,冻结期却在二百四十天以上。大部份区域受树木及其各类生长的植物所复盖,光照时间又短,大量土壤风化作用缓慢。工程地质受季节和阳光幅射较长的阳坡上的二、三级阶地 Permafrost is widespread in the Daxing’an Mountains in northern China. Although the geographical elevation of the area is below the average snow line in China, it is more than 700 meters above sea level, latitude is 45 degrees north, annual average temperature is -2 degrees Celsius, ground temperature is -3 degrees Celsius, and the freezing period is more than 240 days. Most areas are covered by trees and their various types of plants. The light is short and the large amount of soil weathering is slow. The second and third terraces on sunny slopes where the engineering geology is subject to longer seasons and sunlight