Abstract: With the accelerated degradation of permafrost caused by global warming, the problem of slope stability of soil-rock mixture in permafrost regions has become increasingly prominent. To investigate the effects of different water contents and rock contents on the shear strength of soil-rock mixture at the freezing-thawing interface, direct shear tests were carried out on the freezing-thawing interface of soil-rock mixture, and the effects of water content (21%, 24%, 27%, 30%) and rock content (0, 10%, 20%, 30 %, 35%, 40%) on the shear strength of the interface were obtained. The test results show that the effect of water content on the shear strength of the freezing-thawing interface of soil-rock mixture can be divided into two stages: rapid decrease stage and slow decrease stage. The shear strength of the interface decreased rapidly as the water content increased from 21% to 27%, but the decreasing rate slowed down when the water content continued increasing to 30%, suggesting that the threshold value of the water content affecting the shear strength of freezing-thawing interface can be considered to be around 27%. The shear strength of freezing-thawing interface increased with rock content. The shear strength of freezing-thawing interface with the rock content of 10% significantly increased compared to that without rock, with the maximum increase of 33%. When the rock content exceeded 30%, the shear strength would increase rapidly, suggesting that the threshold value of the rock content affecting the shear strength of freezing-thawing interface can be considered to be around 30%. When the rock content was constant, the friction angle of interface gradually decreased with the increase of the water content, and the change tended to be stable after the water content reached 27%. However, the cohesive force at the interface decreased rapidly before the water content increased to 27%, and then decreased slowly. When the water content was constant, the friction angle at the interface increased with the increase of rock content especially when the rock content exceeded 30%. The cohesive force decreased first and then increased slowly with rock content ranging in 0%?30%, but the cohesive force increased rapidly and tended to be flat when the rock content exceeded 30%. When the rock content increased from 0% to 30%, the cohesion force first decreased slightly and then increased gently. After the rock content exceeded 30%, the cohesion force increased rapidly and then leveled off.

Key words: soil-rock mixture, freezing-thawing interface, direct shear teat, permafrost