Abstract: In order to study the changeable characteristics of the hydrothermal field and the salt-expansion deformation laws of salty soil under natural climatic conditions in the northwest arid area of China, vertical apparatuses for monitoring deformation, and sensors for monitoring moisture content and temperature were buried in a test pit of 4.5 meters deep. With the seasonal changes, the different depths of soil temperature field, moisture and salt-expansion deformation of the pit were dynamically monitored for a year and analyzed. The results show that the response to climate change of soil layer within 0.6 meter from the ground is more positive than other soil layers, and the change of temperature is greater. The difference of temperature among the soil layers increases with the proceeding of cooling period. The moisture content of soil is mainly influenced by precipitation, evaporation and temperature gradient; the change of soil moisture above 0.4 meter is more significant than other soil layers, and the water migration along the altitude of the soil shows a zonal phenomenon. Salt-expansion is mainly affected by the temperature and the moisture transfer of soil layers; salt-expansion deformation mainly occurs in the depth of 1.0 meter soil layer from the surface of the earth, which mainly develops in the period from November to February next year.

Key words: salty soil, temperature field, moisture migration, salt-expansion, characteristics of deformation