寒区水电工程陡高开挖边坡的安全稳定是制约高坝大库长期安全运行的重要因素之一，库区陡高岸坡的开挖卸荷松弛拉裂破坏现象显著，成为寒区气候环境引发冻融侵蚀作用的介入通道，进一步造成消落带岸坡岩体的损伤劣化，严重制约着寒区库岸边坡消落带的长期稳定性。以寒区库岸边坡消落带开挖卸荷岩体为研究对象，结合场区气候环境特征与电站运行特点及地质勘察资料，采用室内试验、理论分析、数值仿真相结合的研究方法，探究寒区冻融环境下岸坡消落带开挖卸荷岩体力学特性的演变规律；建立考虑卸荷损伤与冻融侵蚀复合作用下的强度衰减模型，提出寒区岸坡消落带开挖卸荷岩体的力学参数识别方法；并结合工程实例阐释寒区库岸开挖边坡消落带区域冻融致灾破坏模式与防治措施建议。主要研究成果如下： 
（1）基于边坡岩体开挖卸荷力学特征，开展了恒轴压卸围压的室内三轴卸荷试验，通过卸荷阶段的应力应变、变形模量与轴环向围压应变柔量随卸荷量的演化过程，将卸围压阶段可大致分为四个阶段。且卸荷量大于60%后，轴、环向应变围压柔量变化速率明显加快，卸荷损伤逐渐加剧。于此，60%卸荷量为岩样卸荷损伤演化过程的关键分界点。在工程岩体可利用的前提下，选取 60%卸荷量开展岩样的卸荷损伤试验，获取了不同初始围压下的卸荷损伤岩样；通过分析卸荷损伤阶段轴环向卸荷损伤指标，可发现卸荷损伤程度与初始围压大小基本无关、与卸荷量相关；卸荷损伤岩样的单轴加载试验结果，验证了以卸荷量为卸荷损伤划分标准的合理性，以及卸荷损伤试验的可行性。 
（2）根据场区气候环境特征采用自制的岩石冻融夹具，实施了卸荷损伤岩样的冻融循环试验。试验结果表明，卸荷损伤岩样初始围压不同，而冻融后孔隙率平均变化量随冻融次数的演化过程与变化量值大致相同，说明了 60%卸荷量的损伤岩样冻融劣化程度及规律基本一致，与初始围压大小基本无关，故而可利用孔隙率平均变化量衡量卸荷损伤岩样的冻融劣化情况。根据指数衰减模型的推广，结合试验数据拟合的方式修正衰减系数，引入围压值作为衰减参量，并以易于测定的孔隙率平均变化量建立冻融强度衰减模型。 
（3）以岩体的纵波波速为基准量，表征量化广义 Hoek-Brown 准则中的各项岩体力学参数指标，引入岩体完整性系数的修正参量，定量描述坡体不同倾角结构面发育时对开挖卸荷效应的影响，计算得出相应的力学参数，分析开挖卸荷与冻融侵蚀下岸坡岩体力学参数的变化规律。基于算例模型说明了岸坡开挖卸荷分带的划分方法，并对比分析了考虑与不考虑开挖卸荷作用下边坡的变形场，结果表明考虑开挖卸荷效应的计算方法较为符合工程实际。 
（4）以黄河上游某水电工程陡高开挖边坡为例，采用数值计算手段开展边坡动态开挖卸荷应力变形分析，基于考虑开挖卸荷分带的边坡数值计算模型，结合场区气候环境诱发的冻融侵蚀作用与电站运行特征，引入坡体冻融层以及考虑库区蓄水作用，以前述分析计算所得的岩体力学参数为依据，开展考虑岸坡消落带开挖扰动与冻融侵蚀叠加作用下的数值计算分析。发现冻融环境下坡体表层岩体容易破坏，从而出现剥离、脱落，易造成落石等危害，蓄水后存在以软弱或硬性结构面组成的滑坡体，易发生沿结构面的滑动变形，引起边坡的失稳破坏。 

The safety and stability of steep and high excavation slope of hydropower projects in cold area is one of the important factors restricting the long-term safe operation of high dam reservoir. The relaxation and cracking phenomenon of excavation and unloading of steep and high bank slope in reservoir area is significant, which becomes the intervention channel of freezing and thawing erosion caused by the climate environment in cold area, and further causes the damage and deterioration of bank slope rock mass in subsidence zone. It seriously restricts the long-term stability of the subsidence zone of bank slope in cold area. Taking the excavation and unloading rock mass of the bank slope of reservoir in cold region as the research object, combined with the climatic environment characteristics of the site, the operation characteristics of power station and geological investigation data, the research methods of laboratory test, theoretical analysis and numerical simulation were used to explore the evolution law of the mechanical characteristics of rock mass under the freezing and thawing environment of the bank slope slope excavation and unloading. The damage evolution model considering the combined action of unloading damage and freeze-thaw erosion was established, and the identification method of mechanical parameters of excavated unloaded rock mass in the subsidence zone of bank slope in cold region was proposed. Combined with engineering examples, the freezing-thawing disaster failure mode and prevention and control measures in the subsidence zone of excavation slope of reservoir bank in cold area are explained. The main research results are as follows: 
(1) Based on the excavation unloading mechanical characteristics of slope rock mass, an indoor triaxial unloading test of constant axial compression unloading confining pressure was carried out. The unloading stage of confining pressure can be roughly divided into four stages through the evolution of stress-strain, deformation modulus and axial circumferential confining pressure compliance with the unloading amount. When the unloading amount is greater than 60%, the variation rate of axial and circumferential strain confining pressure compliance speeds up obviously, and the unloading damage gradually intensifies. Here, 60% unloading is the key cut-off point in the evolution of unloading damage of rock samples. On the premise that the engineering rock mass is available, 60% unloading volume is selected to carry out the unloading damage test of rock samples, and the unloading damage rock samples under different initial confining pressures are obtained. Through the analysis of the axial circumferential unloading damage index at the unloading damage stage, it can be found that the unloading damage degree is basically unrelated to the initial confining pressure, but related to the unloading volume. The uniaxial loading test results of unloading damaged rock samples verify the rationality of taking unloading amount as the classification standard of unloading damage and the feasibility of unloading damage test. 
(2) According to the climatic and environmental characteristics of the site, the freeze-thaw cycle test of the damaged rock samples under unloading was carried out by using the self-made rock freeze-thaw fixture. The test results show that the initial confining pressure of the damaged rock sample is different, and the evolution process and variation value of the average porosity change after freeze-thaw along with the number of freeze-thaw are roughly the same, indicating that the degree and law of freeze-thaw deterioration of the damaged rock sample with 60% of the unloading amount are basically the same, and have nothing to do with the initial confining pressure. Therefore, the average variation of porosity can be used to measure the freeze-thaw deterioration of unloading damaged rock samples. According to the extension of the exponential attenuation model, the attenuation coefficient was modified by fitting the test data, the confining pressure value was introduced as the attenuation parameter, and the freeze-thaw intensity attenuation model was established with the easily measured average variation of porosity. 
(3) Taking the longitudinal wave velocity of rock mass as the reference quantity, characterizing and quantizing various mechanical parameters of rock mass in the generalized Hoek-Brown criterion, introducing the correction parameter of rock mass integrity coefficient, quantitatively describing the influence of the development of slope structural plane with different dip angles on excavation unloading effect, and calculating the corresponding mechanical parameters. The variation law of mechanical parameters of bank slope rock mass under excavation unloading and freeze-thaw erosion is analyzed. Based on the example model, the partition method of bank slope excavation unloading zone is illustrated, and the deformation field of slope with and without excavation unloading is compared and analyzed. The results show that the calculation method considering excavation unloading effect is more consistent with the engineering practice. 

(4) Taking the steep and high excavation slope of a hydropower project in the upper reaches of the Yellow River as an example, the slope dynamic excavation unloading stress and deformation analysis is carried out by using numerical calculation methods. Based on the slope numerical calculation model considering excavation unloading zonation, combined with the freeze-thaw erosion induced by the climate environment of the site and the operation characteristics of the power station, the slope freeze-thaw layer is introduced and the storage effect of the reservoir area is considered. Based on the mechanical parameters of rock mass calculated by the above analysis, the numerical calculation and analysis were carried out considering the superimposed effects of excavation disturbance and freeze-thaw erosion in the slope subsidence zone. It is found that the surface rock mass of the downhill body is easy to be damaged in freeze-thaw environment, resulting in peeling and falling rock and other hazards. After water storage, there is a landslide body composed of soft or hard structural plane, which is easy to slide deformation along the structural plane and cause the instability of the slope.