Tests and Research on Characteristics of Shear Strength of Cement Improved Soil under Freeze-Thaw Cycle

Roadbed filling undergo at least one freeze-thaw cycle every year in seasonal frozen soil areas, which will lead subgrade to boiling, settlement, strength weakening etc. and has a strong impact on traffic safety and smooth, need to be solved urgently . In recent years, cement improved soil is applied to dissolve frost damage because it can be obtained locally, and has high performance and low price. However, how to evaluate strength of cement soil under repeated freeze-thaw cycles is the key to its further application in those regions. In the paper, the cement improved silty clay is selected as the object which is most common in Heilongjiang roadbed, many groups of freeze-thaw tests and direct shear tests are conducted at different conditions. From these tests, some conclusions about shear strength index and are obtained: 1. the first freeze-thaw cycle has important effect on cohesion of cement soil, during freeze-thaw cycle, the lower temperature is, the faster is decreasing. 2. decreases with freeze-thaw cycles increase, and there is a peak value existing after the seventh cycle, then reduce rapidly. 3. the internal friction angle appears decreasing – increasing–reducing– increasing trend during cycles but the range of change is little. 4. reduces smaller and increases more when temperature is lower.