The Effect of Freeze–Thaw and Moisture on Soil Strength Index of Cutting Slope

Abstract

It is the main problem for highway in seasonal frozen regions that soil cutting slope instability causing by freeze–thaw. The change in soil moisture is important factor for soil cutting slope landsliding. Relying on the silty clay slope, which is in the highway expansion project from Fangzheng to Harbin, using field monitoring, and indoor test, the soil moisture varying with ground temperature and the effect of soil moisture on soil physical and mechanical indexes were studied. Field monitoring result indicates that, during the process of soil freezing, there will appear the cracks caused by temperature shrinkage which destroy integrated strength of the slope. Moisture migrates to the freezing-front due to the cracks caused by temperature shrinkage. In the melting period of spring, because of the accumulating water within the cracks, and longer duration of zero temperature below the surface, the melting water is hampered, when soil body temperature reaches 0.1 °C, the frozen water within the soil body melt rapidly. All of these leads to the water content in shallow slope too high, soil shear strength decreases. Triaxial test results show that: When the soil water content is less than the optimum water content, the soil cohesion increases with increasing moisture, when the soil water content is bigger than the optimum water content, the soil cohesion decreases with increasing moisture. The peak value of soil cohesion is near the optimum water content. The internal friction angle of soil decreases with the increasing moisture. Soil cohesion decreases with the increasing freeze–thaw cycles.