自然界中不同含水状态岩体受冻融循环作用引发内部损伤状况不同，且岩体孔洞、裂隙等不连续结构加速了冻融损伤。因此，开展寒区孔洞缺陷岩体冻融损伤机理与临界饱和度研究，对于岩体工程灾害预测与防治具有十分重要的理论意义与工程价值。以陕北寒区岩质边坡工程为背景，以饱和度60%、70%、80%、90%、100%的椭圆孔缺陷砂岩为研究对象，开展冻融循环前后CT扫描以及单轴压缩试验研究，探究冻融损伤机制以及受荷后力学特性，寻求孔洞缺陷岩石临界饱和度。通过引入细观分形维数，建立不同饱和度椭圆孔缺陷岩石冻融荷载损伤模型，实现细观与宏观内在联系。主要结论如下：
（1）开展五种饱和度椭圆孔缺陷砂岩冻融循环前后CT扫描试验，探究岩石冻融损伤机制与临界饱和度。结果表明砂岩临界饱和度为80%。低饱和度砂岩损伤位于裂隙区域，饱和度超过80%后，岩桥区域开始出现损伤，微裂隙呈连通趋势，孔隙连通性显著增加；冻融前期表现为孔喉平均体积增大、数量增多，冻融后期表现为孔喉扩张、数量减小；低饱和度砂岩在冻融循环后主要导致孔隙间喉道半径扩展并产生更多孔隙，高饱和度砂岩在冻融循环后主要导致相邻孔隙间连通形成微裂隙；椭圆孔缺陷使分凝冰机制更容易发生，低饱和度岩石冻融后损伤较小且冻融循环次数对冻融损伤的程度有限，高饱和度岩石冻融后体积膨胀与产生的静水压力导致微裂隙连通速度快。
（2）采用微机控制岩石力学试验机，开展冻融循环前后单轴压力试验，研究不同饱和度椭圆孔缺陷岩石力学特性。冻融作用对高饱和度砂岩峰值强度和弹性模量影响较大：随着冻融次数的增大，完全饱水岩石峰值强度线性降低，弹性模量拟合曲线呈“上凸型”降低，其余饱和度岩石峰值强度和弹性模量均线性降低；五种饱和度岩石在冻融前期均为拉伸剪切破坏模式，随着饱和度的增加，次生裂纹数量减小，表面剥落程度降低；随着冻融次数的增加，完全饱水岩石由拉伸剪切破坏模式向拉伸破坏模式过渡；岩石宏观裂纹萌生位置起始于椭圆孔尖端，双椭圆孔内尖端产生平行于加载应力方向的拉伸裂纹，剪切裂纹出现在椭圆孔周围的压应力区。
（3）基于Weibull分布岩石荷载损伤模型，以弹性模量表示冻融损伤变量，引入能反映细观损伤的分形维数作为修正参数，创建不同饱和度椭圆孔缺陷岩石冻融荷载损伤模型。利用单轴压缩试验数据计算模型参数，模型曲线与试验曲线相符合，实现了宏细观之间的联系。由损伤模型计算曲线分析冻融荷载总损伤变量与应变的关系，随着冻融次数和饱和度的增加，冻融损伤值增大，冻融增长速率减小，冻融后期较冻融前期损伤值增大一倍。

In nature, different water-bearing rock masses are subjected to freeze-thaw cycles, leading to different internal damage conditions, and discontinuous structures such as rock holes and cracks cause accelerated freeze-thaw damage. For this reason, it is of great theoretical importance and engineering value for the prediction and prevention of rock engineering disasters to investigate the mechanism of freeze-thaw damage and critical saturation of the rock mass with cavity defects in cold regions. Based on the rock slope engineering in the cold region of the northern of the Shaanxi Province, taking the sandstone with elliptical hole defects with saturation of 60 %, 70 %, 80 %, 90 % and 100 % as the research object, the CT scan and uniaxial compression test before and after freeze-thaw cycles were carried out to explore the freeze-thaw damage mechanism and mechanical properties after loading, and to seek the critical saturation of rock with hole defects. By introducing the meso-fractal dimension, the freeze-thaw load damage model of elliptical hole defects with different saturation is established to realize the internal relationship between meso and macro. The main conclusions are as follows: 
(1) To explore the freeze-thaw damage mechanism and critical saturation of the rock, we carried out CT scanning tests before and after freeze-thaw cycles on five saturated elliptical hole defect sandstones. The results show that the critical saturation of sandstone with elliptical hole defects is 80%. The damage of low-saturation sandstone is located in the fracture area. After the saturation exceeds 80 %, the rock bridge area begins to be damaged, the micro-fractures show a connecting trend, and the pore connectivity increases significantly. In the early stage of freezing and thawing, the average volume of pore throat increased and the number increased. In the later stage of freezing and thawing, the pore throat expanded and the number decreased. The low-saturation sandstone mainly leads to the expansion of the throat radius between pores and the generation of more pores after the freeze-thaw cycle, and the high-saturation sandstone mainly leads to the formation of microcracks between adjacent pores after the freeze-thaw cycle. The elliptical hole defect makes the segregation ice mechanism more likely to occur. The freeze-thaw damage of low saturation rocks is small and the number of freeze-thaw cycles has limited effect on the degree of freeze-thaw damage. The volume expansion and hydrostatic pressure of high saturation rock after freeze-thaw lead to fast micro-fracture connectivity.
(2) For uniaxial compression testing before and after freeze-thaw cycles, a microcomputer controlled rock mechanics testing machine was used to investigate the rock mechanical properties of elliptical hole defects with different saturation levels. The freeze-thaw effect has a large influence on the peak strength and elastic modulus of high-saturation sandstone: with the increase of the number of freeze-thaw, the peak strength of fully saturated sandstone decreases linearly, the elastic modulus fitting curve decreases in a 'convex' form, and the peak strength and elastic modulus of other saturated rocks decrease linearly. The five kinds of saturated rocks are tensile shear failure mode in the early stage of freeze-thaw. With increasing saturation, the number of secondary cracks decreases and the degree of surface spalling decreases. With the increase of freeze-thaw cycles, the completely saturated rock transits from tensile shear failure mode to tensile failure mode. The macroscopic crack initiation position of the rock starts from the tip of the elliptical hole. The tip of the double elliptical hole generates tensile cracks parallel to the direction of the loading stress, and the shear crack appears in the zone of compressive stress around the elliptical hole. 
(3) Based on the Weibull distribution rock load damage model, the elastic modulus is used as the variable of freeze-thaw damage, the fractal dimension which can reflect the meso-damage is introduced as the correction parameter, and the freeze-thaw load damage model of elliptical hole defects rock with different saturation is established. Uniaxial compressive test data were used to calculate model parameters. As can be seen from the results, the model curves are consistent with the test curves, which realizes the connection between macroscopic and mesoscopic. The relationship between the total freeze-thaw load damage variable and the deformation is analyzed by the damage model calculation curve. With the increase of the number and saturation of freeze-thaw, the freeze-thaw damage value increased, the freeze-thaw growth rate decreased, and the freeze-thaw damage value doubled in the latter stage compared with the earlier stage.