Seasonal variations in physical properties of shallow soils on the slope of Mt. Gongga, China

Abstract

Soil temperature is the main factor controlling the stability of seasonally frozen soil in high-altitude regions. During the freezing–thawing process, soil water storage and pore water pressure in the slope soil appear to have different variation tendencies with depth and time, which determined the shallow soil transfer to collapse and debris flow. To study the physical properties of shallow soil in these variation trends, an observation station has been constructed on the sunny slope of Mt. Gongga in October 2011. Water content, geothermal temperature and pore water pressures were recorded automatically by sensors on an hourly basis. Through analysis, it was found that felty soil composition (high content of clay with a porous structure) affected the water content and pore water pressure largely; the temperature distribution in the profile showed that the maximum frozen soil depth was about 20 cm below slope surface, and its change in depth presented regularly with index in the coldest and hottest months. Meanwhile, the water content and pore water pressure were reflected by local climate sensitively, and a phenomenon of the time lag was found that the frontal of the water content and pore water pressure was delayed 1 ~ 2 days with increasing depth after rainfall events. The results could provide a guide for further research of the soil water movement and temperature coupling of seasonally frozen soil under freezing– thawing processes in high-altitude regions.