Abstract: Hobson Lake as North Qinghai Province is one of China's most serious soil salinization hazard areas. In recent years, with the rapid development of economy and technology, more and more construction projects will be carried out here. In order to ensure long-term stability and security of the buildings in the area, a scientific inquiry of engineering properties and mechanical properties of saline soil is necessary. Based on the natural accumulated salt and local soil collected from Hobson Lake in September 2015, the indoor frost heave experiment of salted fine sand was performed to study the low temperature characteristics of salted fine sand with low dry density, investigate the mechanism of frost heave of salted fine sand, and analyze the frost shrinkage properties of salted fine sand. Results show as follows: (1)Salted fine sandy with low dry density has great difference in frost heave laws under different moisture conditions. Fine saline soil is frost heave under high moisture content (moisture content 16% and 18%); under low moisture content (moisture content 10% and 12%), the frost heave of fine sand disappears, but the phenomenon of freezing shrinkage appears. Under the critical water content (moisture content 14%), the low temperature characteristic of the saline soil is very special, fine sand occurs cold shrink under the critical moisture content at first, and then the frost emerges as the temperature decreases. (2)Under all moisture contents and salt contents, the volume change of the saline soil is stable at -28℃--30℃, and the increased salinity will reduce the initial occurrence of salted fine sand frost temperature. Furthermore, when the salt content is less than 10%, the frost shrinkage of the soil decreases with the increase of the salt content; when the salt content is more than 10%, freezing shrinkage increases with the increase of salt content, maximum frozen shrinkage is in the middle salt content of 10%. (3)Except for the condition under critical water content, the frost heave and frost shrinkage of salted fine sand with low dry density shows cubic polynomial relation with temperature and linear relation with moisture content. Compared with other water contents, the relationship between the law of frost heave of saline fine sand and temperature under critical moisture is more complex, so the BiDoseResp function was used to fit the frost heave rate data specially, the fitting correlation coefficient is 0.997 59, which is very high. In this paper, the effects of different salt content and water content on the low temperature deformation of saline sandy soil are considered, and the specific relationship between the salt content, water content and temperature are obtained. Find the engineering properties of saline soil has obvious particularity in the cold environment, and the conclusions in this paper can provide valuable theoretical basis for the construction in saline soil area.

Key words: salted fine sand, regulation of frost heave, temperature, moisture content, salt content