Abstract: Indoor cyclic freeze-thaw test was carried out to examine the law of heave and settlement of soft soil under cyclic freezing and thawing as well as the changes in mechanical properties. The expansion and shrinkage of specimen’s volume were measured by changing the number of freeze-thaw cycle; in the meantime, the shear strength of soft soil under different freeze-thaw cycles and varying confining pressure were measured by indoor triaxial test. Test data and microscopic analysis revealed that the rate of volume change augmented with the proceeding of cyclic freezing and thawing; after six freeze-thaw cycles, the heaving rate and settlement rate of soft soil maintained unchanged in general. With the proceeding of cyclic freezing and thawing, the shear strength of soft soil increased first and then decreased, reaching the minimum at the sixth cycle; but finally recovered in the subsequent 6-15 cycles, approa-ching to the value before freezing and thawing. Moreover, freeze-thaw cycle had significant effect on the cohesion of soft clay, but had no correlation with internal friction angle φ.

Key words: soft soil, freeze-thaw cycle, triaxial test, frost heave and thawing settlement, shear strength