土石混合体-混凝土界面在寒区工程广泛分布，其界面处颗粒骨架受冻融影响塌陷、重组，极易诱发界面强度劣化，是影响寒区工程安全运营的难题。解析冻融影响下界面的强度行为，揭示界面强度与孔隙结构和颗粒骨架的互馈效应，是解决此难题的关键。开展土石混合体-混凝土界面室内直剪试验，借助NMR分层测试及PFC数值模拟，获取界面区抗剪强度参数及孔隙结构演化特性，明晰界面颗粒旋转运移特征；基于分形维数理论，定量评价界面孔隙结构变化，阐释冻融下界面强度劣化机理。即强度骤降阶段界面处土石颗粒受冻胀挤压，其有序排列被打乱，联结、互锁作用弱化，此时孔隙体积、分形维数均增大，界面整体性下降；反翘阶段界面处大块土颗粒分裂重组、骨架塌落，形成块石为核、黏土在外覆盖的包裹体结构，孔隙内部复杂程度降低导致抗剪强度小幅提升；随冻融次数增加，碎石外土颗粒剥落，界面区孔隙体积及颗粒旋转量缓慢增大，界面逐渐脱黏劣化。研究成果对工程构筑物孕灾机制具有指导价值。

With implementation of the large-scale development of the western region in China and the Belt and Road Initiative， engineering construction in cold regions is increasing， and the stability problem of the interface between soil-rock mixture and concrete structure is becoming increasingly prominent. Affected by periodic freeze-thaw cycles， the water in the pores of the interface between soil-rock mixture and concrete structure repeatedly freezes and melts， causing changes in the connection and arrangement of soil and stone particles， resulting in loose particle skeleton. It induces cracking of the macroscopic mechanical strength of the interface， and then the occurrence of deformation， dislocation， settlement and other disasters， and keeps safe operation of the project in the cold regions is a difficult problem. The key to solve this problem is to analyze the strength behavior of the interface under the influence of freeze-thaw action， and reveal the mutual feedback effect between the interface strength and pore structure and particle skeleton. In this paper， the indoor direct shear test of soil-rock mixture-concrete interface under different working conditions is carried out to explore the change characteristics of interface shear stress-strain curve， and clarify the influence of freeze-thaw action on the shear strength and strength parameters of soil-rock mixture-concrete interface with different rock content. Then， the NMR layering test and PFC numerical simulation are carried out to obtain the shear strength parameters and pore structure evolution characteristics of the interface area， and to clarify the characteristics of particle rotation and migration at the interface. Based on the fractal dimension theory， quantitatively evaluate the change of interface pore structure， and explain the mechanism of interface strength deterioration under freeze-thaw action： that is， at the stage of strength collapse， the orderly arrangement of the earth and rock particles at the interface is disturbed by the freezing and swelling extrusion， and the coupling and interlocking functions are weakened. At this time， the pore volume and fractal dimension are increased， and the interface integrity is decreased. In the anti-warping stage， the large soil particles at the interface split and recombined， and the skeleton collapsed， forming an inclusion structure with the block stone as the core and the clay covered outside. The reduction in the complexity of the pore interior led to a small increase in the shear strength. With the increase of numbers of freeze-thaw cycles， the soil particles outside the crushed stone peel off， the pore volume and particle rotation in the interface area slowly increase， and the interface gradually debonds and degrades. The interface of low rock content sample is mainly dominated by soil. With the increase of pore volume due to freeze-thaw action， the interface damage and deterioration， the cohesion between soil and concrete decreases， and the shear strength decreases. The shear force is mainly provided at the interface of the high rock sample through the friction and occlusion between the crushed stone and the concrete. Due to the increase of pore volume of the interface layer under freeze-thaw action， the soil-rock mixture becomes loose as a whole， and the cohesion between the crushed stone and the concrete decreases during shearing， and the shear strength shows a downward trend. With the increase of stone content， the interlocking and locking action of the crushed stone at the interface is strengthened， and the shear plane presents an irregular shear band， and the shear strength of the interface increases. The research results have guiding value for the disaster prevention mechanism of engineering structures.