Abstract：Under freeze-thaw cycling，the soil structure was failed，soil porosity was increased，and the pore distribution characteristics was varied，resulting in the degradation of the soil shear performance. A series of tests on lime-soil and fiber-lime-soil，including freeze-thaw test，the triaxial compression test，and NMR test，were completed to research the shear performances and microstructure variation of lime-soil and fiber-lime-soil under freeze-thaw cycling. The results showed that the cohesion and internal friction angle of lime-soil and fiber-lime-soil gradually decreased with the increase of freeze-thaw cycles. The freeze-thaw deterioration was divided into three stages，namely，large strength decline stage，small strength decline stage and strength stability stage. The stress-strain characteristics of lime-soil transformed from strain softening to strain hardening because of adding fibers，and the soil failure form changed from brittle failure to plastic failure. With the increase of freeze-thaw cycles，the porosity and the pore radius of soil increased，the micro pore volume decreased，and the small pore volume，medium pore volume and large pore volume increased. After 10 freeze-thaw cycling，the large pore volume varied little. Because of the spatial restraint effect of fiber on soil and the friction between fiber and soil，the increase of pore radius and porosity of soil were limited to a certain extent，which resulted in the improvement of the shear performance and freeze-thaw resistance of fiber-lime-soil.
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