To study the mechanical characteristics of peat soil under the action of seasonal temperature differences at high altitudes,through the shear strength tests in freeze and freeze thawing in the laboratory,the strength variation law of soil during freeze-thaw was analyzed,and the fitting curve for cohesion of peat soil in freeze-thaw cycles was obtained.The results showed that reducing freeze temperatures and prolon-ging freeze times could increase shear strength of soil,and the freeze time had a more significant effect on the strength;in the process of freeze-thaw,the deterioration effect at the thaw stage on soil strength was greater than that at the freeze stage.The lower the water content was,the greater the deterioration effect was.With the increase in rounds of freeze-thaw cycles,the sensitivity of soil cohesion to the water content decreased,while the sensitivity of internal friction angle to the water content increased.The water content of 51%to 63%was the control threshold of freeze-thaw and lubrication for soil cohesive strength;the dete-rioration of freeze-thaw strength was not only affected by the phase change in pore water,but also affected by the organic matter content.The relation among the round of freeze-thaw cycles,the water content and the soil cohesion was fitted,which could better predict the deterioration of soil strength.
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