Standard for Frozen Soil Layer of Building Foundation in Changsha City, Hunan Province

Frozen soil refers to all kinds of rocks and soils containing ice below zero degrees Celsius. Changsha, Hunan Province is a seasonal frozen soil, which is extremely sensitive to temperature and contains abundant underground ice. Has the following standards:

1 and Changsha non-frozen soil area, the frozen soil thickness is: 0. 1-0.5m, frozen soil begins to appear in 65438+February every year, and gradually disappears in the second half of February.

2. Causes of frozen soil formation. When the seasonal frozen layer is formed in winter, with the freezing front moving from top to bottom, the water in the soil migrates to the freezing front and accumulates ice, and the ice layer and ice lens are mainly concentrated at 2/3 ~ 1/2 of the maximum freezing depth. In Changsha City, Hunan Province, the seasonal thawing layer is mainly frozen from below the surface.

3. The harm of frozen soil. The volume of frozen soil increases, and the resulting frost heave will cause the deformation and destruction of various buildings. When the frozen layer melts, the uneven distribution of ice layer and ice lens leads to the uneven settlement of soil layer, which is an important reason for the deformation and damage of various buildings.

4. The distribution of permafrost in China. Seasonal frozen soil is distributed in all provinces and regions north of the Yangtze River in China, accounting for about 54% of China's land area. Seasonal thawing layer is distributed in permafrost region, and below it is frozen soil layer. From the southern boundary of frozen soil to the north or the lower boundary, the seasonally melted soil layer gradually becomes thinner. Its southern border starts from Zhangfeng, Yunnan, reaches Kunming and Guiyang in the east, surrounds the northern edge of Sichuan Basin, and reaches Changsha, Anqing and Hangzhou. The seasonal freezing depth in southern Heilongjiang Province, northeastern Inner Mongolia and northwestern Jilin Province can exceed 3 meters, and decreases with the decrease of latitude to the south. Permafrost is distributed in Daxing 'anling and Xiaoxing 'anling in the northeast, Altai Mountain, Tianshan Mountain, Qilian Mountain and Qinghai-Tibet Plateau in the west, with a total area of 1/5.