随着“一带一路”和“陆上丝绸之路”等政策的实施，我国西部地区基础设施建设中遇到越来越多裂隙岩石冻融损伤诱发的地质灾害问题。探讨寒区裂隙岩石冻融损伤演化机制对寒区工程建设具有重要意义。本文以天然裂隙砂岩为研究对象，进行了不同冻融作用下的CT无损扫描试验，并引入深度学习理论，基于U-Net网络算法，结合元胞自动机理论，研究了裂隙综合优势角及冻融循环次数对砂岩破坏机制、损伤力学强度特性及其能量场分布的影响，主要完成的工作内容及结论如下：

（1）完成了0、10、20、50、70次冻融裂隙砂岩的CT扫描试验，获得了不同冻融循环作用下裂隙砂岩各个扫描断面的裂隙演化图像，通过阈值分割，实现了天然裂隙砂岩三维结构模型的可视化。（2）在冻融裂隙砂岩CT扫描试验基础上，依据深度学习理论，运用U-Net网络算法，将收缩路径中的高分辨率特征图和扩展路径中的低分辨率特征图有机结合起来，实现了岩石裂隙智能化像素级识别，自动定量获取裂隙的大小、位置等形态参数。（3）采用裂隙长度、宽度、倾角等单一参数描述其对岩石力学性能的影响是不全面的，提出综合优势角描述各裂隙参数对其力学性能的影响。根据冻融砂岩CT扫描试验结果，确定了各岩样的优势角，计算结果表明：随冻融循环次数增加，裂隙网络随机率增大，裂隙分布均匀性增加，优势方向减小。（4）基于元胞自动机理论，将天然裂隙岩石视为由元胞、元胞空间、元胞状态、邻域及更新规则组成的时间维上的动力系统，结合CASRock数值软件，完成了裂隙优势角为45°、60°、75°的岩样在0、10、20、50、70次冻融作用下的破坏机制、力学强度特性及其能量场分布的数值试验。结果表明，由于冻融循环所产生的冻胀力，引起冻融过程中的颗粒分离、孔隙结构变化以及微裂隙的生成和扩展，导致砂岩强度明显降低。裂隙优势角为60°时，裂隙更易扩展，砂岩冻融后强度劣化更大，因此，60°是裂隙砂岩的最不利角，在实际工程中应避免荷载方向与裂隙方向呈此类角度。（5）根据损伤力学理论，考虑细观裂纹扩展，将裂隙砂岩结构视为岩石基质元胞、受荷损伤元胞、冻融损伤元胞及孔裂隙元胞组成的系统，建立了冻融裂隙砂岩损伤本构模型，并与试验结果进行了对比验证。结果表明，该模型能够较好地描述冻融裂隙砂岩的损伤演化过程。损伤初始值随冻融循环次数的增加逐步增加，但增幅却逐渐减小；裂隙优势角为60°时的砂岩初始损伤值较低，呈现结构面产状效应。相关研究成果为后续探究天然裂隙岩石内部细观结构演化提供了理论基础。

With the implementation of policies such as ' The Belt and Road ' and ' Land Silk Road ', more and more geological disasters induced by freeze-thaw damage of fractured rock are encountered in infrastructure construction in western China. It is of great significance to explore the evolution mechanism of freeze-thaw damage of fractured rock in cold regions for engineering construction in cold regions. In this paper, the natural fractured sandstone is taken as the research object, and the CT non-destructive scanning test under different freeze-thaw cycles is carried out. Based on the U-Net network algorithm and the cellular automata theory, the influence of the comprehensive advantage angle of the fracture and the number of freeze-thaw cycles on the failure mechanism, damage mechanical strength characteristics and energy field distribution of sandstone is studied. The main work and conclusions are as follows :

(1) The CT scanning tests of 0,10,20,50 and 70 times of freeze-thaw fractured sandstone were completed, and the fracture evolution images of each scanning section of fractured sandstone under different freeze-thaw cycles were obtained. (2) Based on the CT scanning test of freeze-thaw fractured sandstone, according to the deep learning theory, the U-Net network algorithm is used to combine the high-resolution feature map in the shrinkage path with the low-resolution feature map in the expansion path. The intelligent pixel-level identification of rock fractures is realized, and the morphological parameters such as the size and location of fractures are automatically and quantitatively obtained. (3) It is not comprehensive to describe the influence of single parameters such as crack length, width and dip angle on rock mechanical properties. According to the results of CT scanning test of freeze-thaw sandstone, the dominant angle of each rock sample is determined. The calculation results show that with the increase of freeze-thaw cycles, the random rate of fracture network increases, the uniformity of fracture distribution increases, and the dominant direction decreases. (4) Based on the theory of cellular automata, the natural fractured rock is regarded as a dynamic system on the time dimension composed of cells, cellular space, cellular state, neighborhood and update rules. Combined with CASRock numerical software, the failure mechanism, mechanical strength characteristics and energy field distribution of rock samples with fracture dominant angles of 45°, 60° and 75° under 0,10,20,50 and 70 freeze-thaw cycles are completed. The results show that due to the frost heave force generated by the freeze-thaw cycle, the particle separation, pore structure change and the formation and expansion of microcracks during the freeze-thaw process are caused, resulting in a significant decrease in the strength of sandstone. When the dominant angle of fracture is 60 °, the fracture is more likely to expand, and the strength degradation of sandstone after freeze-thaw is greater. Therefore, 60° is the most unfavorable angle of fractured sandstone. In practical engineering, such an angle between load direction and fracture direction should be avoided. (5) According to the theory of damage mechanics, considering the meso-crack propagation, the fractured sandstone structure is regarded as a system composed of rock matrix cell, loaded damage cell, freeze-thaw damage cell and pore crack cell. The damage constitutive model of freeze-thaw fractured sandstone is established and compared with the experimental results. The results show that the model can better describe the damage evolution process of freeze-thaw fractured sandstone. The initial damage value increased gradually with the increase of freeze-thaw cycles, but the increase rate decreased gradually. The initial damage value of sandstone with the dominant angle of 60° is lower, showing the occurrence effect of structural plane. The relevant research results provide a theoretical basis for the subsequent exploration of the internal microstructure evolution of natural fractured rock.