随着“丝绸之路新经济带”国家战略的实施，寒区岩土工程规模增加。岩石作为一种含有原始缺陷的非均质脆性材料，在冻融环境下的破坏形态受非均质影响显著，造成寒区工程建设存在安全隐患。本文以寒区岩土工程为背景，针对冻融岩石开展CT扫描试验，基于图像处理技术、结合损伤力学及数值模拟，从细观角度对非均质岩石的冻融损伤力学演化规律开展研究。主要研究内容及结论如下：

        (1) 选取陕西红砂岩开展冻融循环试验，对冻融岩石进行CT扫描和不同围压下的力学特性试验，分析不同冻融次数下岩石CT扫描图像及力学特性变化规律。结果表明：红砂岩呈现出颗粒脱落及片状剥落两种劣化模式。随冻融次数的增加，CT图像颜色加深，反映出冻融红砂岩细观结构的损伤变化情况。围压相同时，岩石弹性模量和极值应力随冻融次数增加呈下降趋势；冻融次数相同时，随围压增大呈增加趋势。

(2) 对CT图像进行图像增强、直方图均衡化、阈值分割及三维可视化处理，提取了三维可视化重构模型的体孔隙率及体分形维数以定量表征孔隙大小及结构形态。结果表明：图像处理后的二维CT图像及三维模型可清晰展示岩石各截面和空间内不同介质(岩石基质和孔隙基质)的分布；随冻融次数的增加，体孔隙率增大而体分形维数减小，表明岩石内部孔隙扩展连通导致数量增多，结构形态复杂度降低。

(3) 对岩石非均质特征提取量化，考虑非均质性造成岩石细观局部破裂，提出孔隙发育阈度来定义冻融细观损伤变量，并引入冻融岩石损伤本构模型。结果表明：冻融岩石二维CT图像中孔隙不均匀分布且具有方向性；非均质系数随冻融次数的增加而降低，表明岩石内部孔隙疏密区间差异度下降；冻融细观损伤变量与宏观损伤变量演化规律一致；本构模型理论曲线与试验曲线吻合度较高，所建模型能够反映冻融岩石变形破坏全过程。

(4) 通过Python软件实现孔隙随机分布，导入ABAQUS有限元软件建立了含孔隙分布的岩石非均质模型，模拟岩石在冻融环境下的劣化模式。基于统计失效单元个数定义了冻融损伤值。结果表明：冻融作用下，孔隙处产生应力集中，岩石损伤劣化从孔隙单元逐渐不均匀扩散，最终导致岩石外表层产生脱落。通过统计不同冻融次数下失效单元个数计算出的损伤值，与有效承载体积所计算的较为接近，表明非均质模型具有合理性。

(5) 基于多元线性回归和指数衰减函数，考虑岩石非均质性进行断层划分，建立了冻融红砂岩强度衰减预测模型。结果表明：预测结果与试验结果的误差不超过6.8%，通过细观结构变化能够精准预测非均质岩石的宏观强度特性，为寒区工程的安全稳定性评价提供了有益参考。

With the implementation of the national strategy of "Silk Road New Economic Belt", the scale of geotechnical engineering in cold areas has increased. As a kind of heterogeneous brittle material with original defects, rock failure form is significantly affected by heterogeneity in freeze-thaw environment, which leads to security risks in engineering construction in cold area. In this thesis, based on the background of geotechnical engineering in cold region, CT scanning tests were carried out for freeze-thaw rocks. Based on image processing technology, combined with damage mechanics and numerical simulation, the evolution law of freeze-thaw damage mechanics of heterogeneous rocks was studied from a mesoscopic perspective. The main research contents and conclusions are as follows:

(1) Shaanxi red sandstone was selected to carry out freeze-thaw cycle test, and CT scanning and mechanical properties tests were conducted on freeze-thaw rocks under different confining pressures to analyze the changes of CT scanning images and mechanical properties of rocks under different freeze-thaw times. The results show that the red sandstone presents two deterioration modes: particle shedding and flake spalling. With the increase of freeze-thaw times, the color of CT image is deepened, which reflects the damage changes of the microstructure of freeze-thaw red sandstone. When confining pressure is the same, the elastic modulus and extreme stress of rock decrease with the increase of freeze-thaw times. When the number of freeze-thaw is the same, it increases with the increase of confining pressure.

(2) Image enhancement, histogram equalization, threshold segmentation and 3D visualization were performed on CT images, and the volume porosity and fractal dimension of the 3D visualization reconstructed model were extracted to quantitatively characterize the pore size and structure. The results show that the 2D CT images and 3D models after image processing can clearly show the distribution of different media (rock matrix and pore matrix) in different sections and Spaces of rock. With the increase of freezing-thawing times, the volume porosity increases while the fractal dimension decreases, indicating that the expansion and connectivity of pores in the rock leads to an increase in the number and a decrease in the complexity of structural morphology.

(3) Extraction and quantification of rock heterogeneity features, considering the local mesoscopic fracture caused by heterogeneity, pore development threshold was proposed to define freeze-thaw mesoscopic damage variables, and the freeze-thaw rock damage constitutive model was introduced. The results show that the pores in two-dimensional CT images of freeze-thaw rocks are unevenly distributed and directional. The heterogeneity coefficient decreases with the increase of freezing-thawing frequency, indicating that the difference of pore density interval decreases. The evolution law of freeze-thaw mesoscopic damage variables is consistent with that of macro damage variables. The theoretical curve of the constitutive model is in good agreement with the experimental curve, and the model can reflect the whole process of deformation and failure of freeze-thaw rock.

(4) The random distribution of pores was realized by Python software, and the heterogeneous model of rocks with pore distribution was established by importing the finite element software ABAQUS to simulate the deterioration mode of rocks under freeze-thaw environment. The freeze-thaw damage value was defined based on the number of statistical failure units. The results show that: under the action of freeze-thaw, stress concentration occurs in the pores, and the damage and deterioration of the rock gradually diffuse unevenly from the pore units, and eventually lead to the fall off of the outer surface of the rock. The damage value calculated by counting the number of failure units under different freeze-thaw times is close to that calculated by the effective bearing volume, which indicates that the heterogeneous model is reasonable.

(5) Based on multiple linear regression and exponential attenuation function, the strength attenuation prediction model of freeze-thaw red sandstone is established by fault division considering rock heterogeneity. The results show that the error between the predicted results and the experimental results is less than 6.8%. The macro strength characteristics of heterogeneous rocks can be accurately predicted through the mesostructural changes, which provides a useful reference for the safety and stability evaluation of engineering in cold areas.

[1] 李宁, 程国栋, 谢定义. 西部大开发中的岩土力学问题[J]. 岩土工程学报, 2001(3): 268-272.

[2] 杨更社, 申艳军, 贾海梁, 等. 冻融环境下岩体损伤力学特性多尺度研究及进展[J]. 岩石力学与工程学报, 2018, 37(3): 545-563.

[3] Qureshi M U, Towhata I, Yamada S. Experimental relation between shear strength under low pressure and S-wave velocity of rock subjected to mechanical weathering[J]. Soils and Foundations, 2019, 59(5): 1468-1480.

[4] Park J, Hyun C U, Park H D. Changes in microstructure and physical properties of rocks caused by artificial freeze–thaw action[J]. Bulletin of Engineering Geology and the Environment, 2015, 74: 555-565.

[5] Del Roa L M, Lopez F, Esteban F J, et al. Ultrasonic study of alteration processes in granites caused by freezing and thawing[C]//2005 IEEE Ultrasonics Symposium. 2005, 1: 415-418.

[6] Ghobadi M H, Babazadeh R. Experimental studies on the effects of cyclic freezing–thawing, salt crystallization, and thermal shock on the physical and mechanical characteristics of selected sandstones[J]. Rock Mechanics and Rock Engineering, 2015, 48: 1001-1016.

[7] Khanlari G, Abdilor Y. Influence of wet–dry, freeze–thaw, and heat–cool cycles on the physical and mechanical properties of Upper Red sandstones in central Iran[J]. Bulletin of Engineering Geology and the Environment, 2015, 74: 1287-1300.

[8] Momeni A, Abdilor Y, Khanlari G R, et al. The effect of freeze–thaw cycles on physical and mechanical properties of granitoid hard rocks[J]. Bulletin of Engineering Geology and the Environment, 2016, 75: 1649-1656.

[9] Javad E, Charlotte W, Anne-Lise B, et al. Influence of physical and mechanical properties on the durability of limestone subjected to freeze-thaw cycles[J]. Construction and Building Materials, 2017, 162, 420-429.

[10] Winkler E M. Frost damage to stone and concrete: geological considerations[J]. Engineering Geology, 1968, 2(5): 315-323.

[11] 张慧梅, 雷利娜, 杨更社. 等围压条件下岩石本构模型及损伤特性[J]. 中国矿业大学学报, 2015, 44(1): 59-63.

[12] 张慧梅, 夏浩峻, 杨更社, 等. 冻融循环和围压对岩石物理力学性质影响的试验研究[J]. 煤炭学报, 2018, 43(2): 441-448.

[13] 吕伍杨. 温度对岩石物理力学特性的影响研究[J]. 内蒙古科技与经济, 2018(7): 68-70.

[14] 刘向峰, 郭子钰, 王来贵, 等. 冻融循环作用下石窟砂岩物理力学性质损伤规律研究[J]. 试验力学, 2020, 35(5): 943-954.

[15] 赵建军, 解明礼, 余建乐, 等. 冻融作用下含裂隙岩石力学特性及损伤演化规律试验研究[J]. 工程地质学报, 2019, 27(6): 1199-1207.

[16] 李宁, 张平, 程国栋. 冻结裂隙砂岩低周循环动力特性试验研究[J]. 自然科学进展, 2001, 11(11): 1175-1180.

[17] 何国梁, 张磊, 吴刚. 循环冻融条件下岩石物理特性的试验研究[J]. 岩土力学, 2004, 25(S2): 52-56.

[18] 徐光苗, 刘泉声, 彭万巍, 等. 低温作用下岩石基本力学性质试验研究[J]. 岩石力学与工程学报. 2006(12): 2502-2508.

[19] 刘慧, 蔺江昊, 杨更社, 等.冻融循环作用下砂岩受拉损伤特性的声发射试验[J]. 采矿与安全工程学报, 2021, 38(4): 830-839.

[20] 乔趁, 王宇, 宋正阳, 等.饱水裂隙花岗岩周期冻胀力演化特性试验研究[J]. 岩土力学, 2021, 42(8): 2141-2150.

[21] 杨更社, 申艳军, 贾海梁, 等. 冻融环境下岩体损伤力学特性多尺度研究及进展[J]. 岩石力学与工程学报, 2018, 37(3): 545-563.

[22] 张二锋, 杨更社, 刘慧. 冻融循环作用下砂岩细观损伤演化规律试验研究[J]. 煤炭工程, 2018, 50(10): 50-55.

[23] 色麦尔江·麦麦提玉, 苏普, 朱珍德. 冻融循环作用下卸荷砂岩微观损伤特性试验研究[J]. 矿业研究与开发, 2020, 40(2): 76-81.

[24] 李杰林, 朱龙胤, 周科平, 等. 冻融作用下砂岩孔隙结构损伤特征研究[J]. 岩土力学, 2019, 40(9): 3524-3532.

[25] Senocak D, Pennell S P, Gibson C E, et al. Effective use of heterogeneity measures in the evaluation of a mature CO2 flood[C]//SPE Symposium on Improved Oil Recovery. OnePetro, 2008.

[26] Roy B, Anno P, Gurch M. Imaging oil-sand reservoir heterogeneities using wide-angle prestack seismic inversion[J]. The Leading Edge, 2008, 27(9): 1192-1201.

[27] Kwon S I, Sung W M, Huh D G, et al. Characterization of heterogeneity using inverse model equipped with parallel genetic algorithm[C]//SPE Asia Pacific Oil and Gas Conference and Exhibition. OnePetro, 2004.

[28] 罗明高. 定量储层地质学[M]. 北京: 地质出版社, 1998.

[29] 刘泽容, 信荃麟, 王伟锋, 等. 油藏描述原理与方法技术[M]. 北京: 石油工业出版社, 1993.

[30] 董桂玉, 何幼斌, 徐徽, 等. 储层宏观非均质性的几种表征方法[J]. 石油天然气学报(江汉石油学院学报), 2005, (S4): 56-57.

[31] 胡越, 孟元林. 储层渗透率变异系数算法研究—以茨榆坨采油厂牛 74 块为例[J]. 价值工程, 2015, 34(15): 220-222.

[32] Zhao Y, Liu S, Zhao G F, et al. Failure mechanisms in coal: Dependence on strain rate and microstructure[J]. Journal of Geophysical Research: Solid Earth, 2014, 119(9): 6924-6935.

[33] Zhang R, Ai T, Li H, et al. 3D reconstruction method and connectivity rules of fracture networks generated under different mining layouts[J]. International Journal of Mining Science and Technology, 2013, 23(6): 863-871.

[34] 孙华飞, 杨永明, 鞠杨, 等. 开挖卸荷条件下煤岩变形破坏与能量释放的数值分析[J].煤炭学报, 2014, 39(2): 258 -272.

[35] Kaiser P K, Tang C A. Numerical simulation of damage accumulation and seismic energy release during brittle rock failure—Part II: Rib pillar collapse[J]. International Journal of Rock Mechanics and Mining Sciences, 1998, 35(2): 123-134.

[36] Zhitao M, Yunliang T, Ting Z. Modeling of rock failure based on physical cellular automata[J]. Journal of Southeast University(English Edition), 2005, 21(3): 348-352.

[37] 吕兆兴, 冯增朝, 赵阳升. 岩石的非均质性对其材料强度尺寸效应的影响[J]. 煤炭学报, 2007, 32(9): 917-920.

[38] 冯增朝, 赵阳升, 段康廉. 岩石的细胞元特性及其非均质分布对岩石全曲线性态的影响[J]. 岩石力学与工程学报, 2004, 23(11): 1819-1823.

[39] 王家禄, 高建, 刘莉. 应用CT技术研究岩石孔隙变化特征[J].石油学报, 2009, 30(06): 887-893+897.

[40] 宋红华, 赵毅鑫, 姜耀东, 等. 单轴受压条件下煤岩非均质性对其破坏特征的影响[J].煤炭学报, 2017, 42(12): 3125-3132.

[41] 刘玉龙, 汤达祯, 许浩, 等. 基于X-CT技术不同煤岩类型煤储层非均质性表征[J]. 煤炭科学技术, 2017, 45(3): 141-146.

[42] 朱万成, 康玉梅, 杨天鸿, 等. 基于数字图像的岩石非均匀性表征技术在流固耦合分析中的应用[J]. 岩土工程学报, 2006(12): 2087-2091.

[43] 高经纬, 席岩, 范立峰, 等. 热损伤花岗岩内细观裂隙分布非均匀性的研究[J]. 实验力学, 2021, 36(3): 350-358.

[44] 韩越祥, 万璋. 基于经纬分析法研究热损伤岩石的非均匀性和各向异性[J]. 工业建筑, 2018, 48(1): 114-117.

[45] 傅宇方, 梁正召, 唐春安. 岩石介质细观非均匀性对宏观破裂过程的影响[J]. 岩土工程学报, 2000, 22(6): 705-710.

[46] 黄明利, 唐春安. 非均匀因素对I型裂纹扩展、相互作用影响的数值分析[J]. 岩石力学与工程学报, 2002, 21(8): 1111-1114.

[47] Fang Z, Harrison J P. A mechanical degradation index for rock[J]. International Journal of Rock Mechanics and Mining Sciences, 2001, 38(8): 1193-1199.

[48] Fang Z, Harrison J P. Development of a local degradation approach to the modelling of brittle fracture in heterogeneous rocks[J]. International Journal of Rock Mechanics and Mining Sciences, 2002, 39(4): 443-457.

[49] Yuan S C, Harrison J P. A review of the state of the art in modelling progressive mechanical breakdown and associated fluid flow in intact heterogeneous rocks[J]. International Journal of Rock Mechanics and Mining Sciences, 2006, 43(7): 1001-1022.

[50] Liu H Y, Kou S Q, Lindqvist P A, et al. Numerical studies on the failure process and associated microseismicity in rock under triaxial compression[J]. Tectonophysics, 2004, 384(1-4): 149-174.

[51] 陈永强, 郑小平, 姚振汉. 三维非均匀脆性材料破坏过程的数值模拟[J]. 力学学报, 2002, 34(3): 351-361.

[52] 王学滨. 峰后脆性对非均质岩石试样破坏及全部变形的影响团. 中南大学学报(自然科学版), 2008, 39(5): 2394-2399.

[53] 刘建, 赵国彦, 梁伟章, 等. 非均匀岩石介质单轴压缩强度及变形破裂规律的数值模拟[J]. 岩土力学, 2018, 39(S1): 505-512.

[54] 胡训健, 卞康, 谢正勇, 等. 细观结构的非均质性对花岗岩强度及变形影响的颗粒流模拟[J]. 岩土工程学报, 2020, 42(8): 1540-1548.

[55] 傅宇方, 梁正召, 唐春安. 岩石介质细观非均匀性对宏观破裂过程的影响[J]. 岩土工程学报, 2000, (6): 705 -710.

[56] 尚俊龙, 胡建华, 周科平. 单轴加载岩石损伤及声发射特性非均质效应的数值试验[J].中南大学学报(自然科学版), 2013, 44(6): 2470-2475.

[57] 杨天鸿, 谭国焕, 唐春安, 等. 非均匀性对岩石水压致裂过程的影响[J]. 岩土工程学报, 2002, (6): 724-728.

[58] 李明, 郭培军, 梁力, 等. 含有硬包裹体分布的非均质岩石水力压裂特性研究[J]. 岩土力学, 2016, 37(11): 3130-3136.

[59] 李静, 周汉国, 刘思萌, 等. 基于数字图像处理的非均质岩石材料细观尺度应力分析[J]. 中国石油大学学报(自然科学版), 2016, 40(6): 143-149.

[60] 张德海, 朱浮声, 邢纪波, 等. 岩石类非均质脆性材料破坏过程的数值模拟[J]. 岩石力学与工程学报, 2005, (4): 570-574.

[61] 中华人民共和国住房和城乡建设部. GB/T 50266-2013 工程岩体试验方法标准[S]. 北京: 中国计划出版社, 2013.

[62] 谢和平. 分形几何及其在岩土力学中的应用[J]. 岩土工程学报, 1992, 14: 14-24.

[63] 谢和平. 分形-岩石力学导论[M]. 北京: 科学出版社, 1996.

[64] Zhou H W, Xie H. Direct estimation of the fractal dimensions of a fracture surface of rock[J]. Surface Review and Letters, 2003, 10(05): 751-762.

[65] 姜广辉. 高温处理后岩石内部结构演化及波速渗透率关系研究[D]. 北京: 中国矿业大学, 2018.

[66] 高经纬. 基于X-ray CT技术花岗岩细观特性的热效应研究[D]. 北京工业大学, 2018.

[67] 张慧梅, 雷利娜, 杨更社. 基于Weibull统计分布的岩石损伤模型[J]. 湖南科技大学学报(自然科学版), 2014, 29(3): 29-32.

[68] 张慧梅, 孟祥振, 彭川, 等. 冻融-荷载作用下基于残余强度特征的岩石损伤模型[J]. 煤炭学报, 2019, 44(11): 3404-3411.

[69] 张慧梅, 孟祥振, 彭川, 等. 岩石变形全过程冻融损伤模型及其参数[J]. 西安科技大学学报, 2018, 38(2): 260-265.

[70] MUTLUTÜRK M, ALTINDAG R, TÜRK G. A decay function model for the integrity loss of rock when subjected to recurrent cycles of freezing-thawing and heating-cooling[J]. International Journal of Rock Mechanics and Mining Sciences, 2004, 41(2): 237−244.

[71] Eslami J, Walbert C, Beaucour A L, et al. Influence of physical and mechanical properties on the durability of limestone subjected to freeze-thaw cycles[J]. Construction and Building Materials, 2018, 162: 420-429.

[72] 蔡原田. 不同饱和度红砂岩冻融损伤特性研究[D]. 武汉: 武汉科技大学, 2020.

[73] Bayram F. Predicting mechanical strength loss of natural stones after freeze–thaw in cold regions[J]. Cold Regions Science and Technology, 2012, 83: 98-102.

[74] 谢和平, 陈忠辉. 岩石力学[M]. 北京: 科学出版社, 2004.

[75] 刘强. 不同干湿状态下沥青混合料细观水损规律分析[D]. 邯郸: 河北工程大学, 2021.