To investigate mechanical properties of active layer in permafrost due to the freeze-thaw cycles

a series of the unconsolidated and undrained triaxial shear tests were conducted by considering the factors of different freezing temperatures

degree of compaction

numbers of freeze-thaw cycles

moisture content and confining pressures. The stress-strain curve

failure strength

elastic modulus and shear strength parameters of sandy silt were determined and analyzed

and significance analysis of the five factors and interactions among of them were carried out. Results show that with the increase of freeze-thaw cycles

the failure strength and elastic modulus

measured at the confining pressures of 300 kPa and at the freezing temperatures of -5 ℃

increase at the first three freeze-thaw cycles and then attain a stable status. Cohesion force decreases gradually and tends to be stable at the freezing temperatures of -5 ℃

and increase firstly and then drop

finally attain a stable status at the freezing temperatures of -10 ℃ and -15 ℃. All factors have a significant influence on the mechanical properties except freezing temperature. Interactions between degree of compaction and moisture content

confining pressure and number of freeze-thaw cycles exhibit a significant effect on failure strength. Significant analysis indicates that interactions of factors should be considered in the test design.