THE IMPACT OF FREEZE–THAW ON SOIL CUT SLOPE STABILITY AND REINFORCEMENT OF SHRUB ROOTS IN HIGH-LATITUDE FROZEN REGIONS

It has been widely reported that seasonally-frozen is one of the major factors of soil cut slope instability. The effect of freeze–thaw cycles on the stability of seasonally-frozen cut slope along Fangzheng-Harbin expressway was studied. A comprehensive study on soil cut slope stability and reinforcement of shrub roots was carried out by combining results obtained from field monitoring tests, laboratory experiments and numerical simulations. Field monitoring result indicates that during the process of soil freezing, moisture content of the soil increases to the freezing front, and forms ice segregates in some parts of the frozen area. In spring, when snow melts and temperature increases above zero temperature, 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. Triaxial test results show that Soil shear strength changes with the water content regularly; Soil cohesion decrease with increasing 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 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. Slope shallow soil moisture could be adjusted effectively by plant transpiration, and plant roots and soil could form root-soil complex, these could make soil cut slope stability.