The Impact of Freeze–thaw on the Stability of Soil Cut Slope in High-latitude Frozen Regions

Abstract

It has been widely reported that variations in soil moisture content is one of the factors that contribute to landslide occurrence in cut slopes. The effect of freeze–thaw cycles on the stability of seasonally-frozen cut slope along Fangzheng-Harbin expressway was studied. A comprehensive study on the silty clay material of the cut slope was carried out by combining results obtained from field monitoring tests, laboratory experiments and numerical simulations. Also, the variation of soil moisture content with subsurface temperature and the impact of soil moisture content on the physical and mechanical index properties of the soil were studied. Results obtained from finite element analysis shows that soil moisture content contribute to instability of the cut slope especially in spring periods of snow melt. Field monitoring result indicates that during the process of soil freezing, moisture content of the soil decreases to the freezing front, and forms ice segregates in some parts of the frozen area. In spring, when snow melts and temperature increases to 0 °C, increase in temperature stops temporarily, and soil moisture rises slowly. After a period of time, the soil moisture curve rises rapidly, followed by the rapid rising in soil temperature. This phenomenon is due to the absorption of heat by the frozen layer due to ice melting process. Triaxial test results show that when the soil moisture content is less than optimum moisture, soil cohesion increases with increase in moisture, while when the soil water content is higher than the optimum water content, soil cohesion decreases with increase in moisture. The peak value of soil cohesion is near the optimum water content. The internal friction angle of the soil decreases with increasing moisture content. Soil cohesion decreases with increasing freeze–thaw cycles. The internal friction angle of the soil increases after the first freeze–thaw cycle, but it decreases in later freeze–thaw cycles. Finite element analysis results show that factor of safety of the slope decreases with increase in soil moisture. Results obtained from physical and mechanical parameters of the cut slope material in K560+700 section is in critical unstable state. This is validated by comparing the physical and mechanical parameters from another shrub slope in K563+870 section which is in a more stable state. This simulation result is consistent with the actual situation. It follows that moisture content in the soil mass accumulates to frozen areas in the freezing process, and rapid increase of the soil moisture in shallow layer of the slope during the thawing period is the main reason for the instability of cut slope.