变形局部化是寒区岩土工程失稳的重要表现形式和破坏先兆信息，开展单轴压缩荷载作用下冻融岩石局部化特征研究对于寒区工程稳定性具有重要意义。本文以冻融红砂岩为研究对象，应用理论研究、试验研究和数值模拟相结合的方法，对冻融砂岩变形局部化产生、演化、形成宏观剪切带及失稳破坏过程进行了系统研究。主要研究工作及成果如下：

（1）在对常温下岩石变形局部化理论进行分析的基础上，基于梯度塑性理论和岩石变形破坏的本构关系，推导出冻融岩石变形局部化带宽度理论。根据冻融砂岩在单轴压缩条件下的CT扫描试验结果，得到不同冻融循环次数下砂岩变形局部化带宽理论值和实测值，对所推导的公式进行了验证：理论值与实测值较为接近，可以较好预测冻融循环30次内的岩石变形局部化带宽度。

（2）开展了冻融砂岩单轴压缩破坏全过程的声-热信息多元监测试验。根据试验结果，从声发射能量、振铃计数、累计振铃计数、幅值和最高红外辐射温度、平均红外辐射温度、红外热像序列图等不同声热参数对冻融砂岩局部化产生、演化、宏观剪切带形成及失稳破坏过程进行了系统全面的分析。结果表明：随着冻融循环次数增加，声发射信号幅值条带状分布特征减弱。冻融岩石在荷载作用下会发生临界慢化现象，当荷载临近屈服点时，出现岩样内部初始损伤发育及损伤集中扩展现象，且随冻融循环次数增加，这种不可逆的损伤恢复到初始状态的能力减弱，岩石变形局部化现象增强。冻融砂岩在单轴压缩荷载作用下经历了初始微裂纹（孔隙）压密→微裂纹新生→裂隙逐渐贯通产生变形局部化→局部化带形成、扩大直至宏观主裂纹产生的过程。冻融岩石变形局部化带的产生及演化本质是能量累积、耗散及释放的动态过程。

（3）运用声发射三维定位技术对变形局部化位置进行精确定位，进一步研究了冻融砂岩变形局部化空间破坏特征。结果表明：在应力为0.8~，大量声发射事件发生，事件点分布逐渐由无序向有序发展，声发射事件成核成团，岩石内部出现变形局部化现象。在峰后阶段，众多微裂纹延伸汇聚形成多条局部化剪切带，且局部化带向外扩展最终形成宏观主裂纹，此时冻融岩样内部出现大量高能量事件点。冻融岩石的破坏是内部多条变形局部化带共同作用的结果。岩石变形局部化带的形成是一个逐渐累积渐进的过程，冻融岩石变形局部化带最先形成于岩石中部，初始损伤位置是局部化带形成位置及岩石破坏模式的重要影响因素。

（4）基于冻融砂岩单轴压缩声-热多元监测试验结果，提出了用于定量描述冻融砂岩局部化破坏过程的4个声-热分析指标：自相关系数、变异系数、时间熵值和空间熵值，揭示了冻融砂岩加载破坏过程局部化损伤的时间特征。结果表明：声发射自相关系数和变异系数突变点可作为岩石变形局部化带形成时间点判据，时间熵值和空间熵值曲线的变化规律反映出岩石变形局部化阶段。砂岩局部化破坏时间随冻融次数增加而提前。

（5）提出声-热联合指标，完成了冻融岩石声-热变形局部化时间特征和结构特征的分析。压缩荷载作用下不同冻融次数砂岩变形局部化产生的时序关系为：30次冻融砂岩＜20次冻融砂岩＜10次冻融砂岩＜5次冻融砂岩＜未冻融砂岩。变形局部化程度为：未冻融砂岩＞5次冻融砂岩＞10次冻融砂岩＞20次冻融砂岩＞30次冻融砂岩。冻融循环作用改变了岩石内部孔隙结构大小、数量和分布特征，进而引起破裂过程中声-热变形局部化特性的改变。通过声发射和热成像不同指标下砂岩变形局部化现象产生时间敏感性分析发现，声发射累计振铃对岩石变形局部化产生较事件点更为敏感。自相关系数对于描述岩石变形局部化敏感性程度更具有优势。将热成像技术和声发射技术联合应用于预测寒区岩石变形局部化产生，能够提高灾变前兆识别的可靠性。

（6）基于细胞自动机理论，运用弹塑性细胞自动机软件CASrock建立了含初始损伤砂岩的三维数值计算模型，完成了不同损伤位置、损伤尺寸、损伤间距岩石的单轴压缩破坏过程数值试验。通过分析各组试样表面和内部的岩体破坏程度（RFD）、等效塑性剪应变（Epstn）、等效拉伸应变（Epttn）及局部能量释放率（LERR）云图，发现：损伤位于中部的砂岩破坏时间最短，损伤尺寸对岩石最终破坏形态有重要影响，而损伤间距对砂岩损伤扩展方向影响较大。

Deformation localization is an important manifestation and failure precursor information of geotechnical engineering instability in cold regions. It is of great significance to study the localization characteristics of frozen-thawed rock under uniaxial compression load for the stability of geotechnical engineering in cold regions. In this paper, the freeze-thaw red sandstone is taken as the research object, and the method of combining theoretical research, experimental research and numerical simulation is used to systematically study the generation, evolution, formation of macroscopic shear bands and instability failure process of freeze-thaw sandstone deformation localization. The main research work and achievements are as follows :

Based on the analysis of the theory of rock deformation localization at room temperature, based on the gradient plasticity theory and the constitutive relationship of rock deformation and failure, the theory of deformation localization band width of freeze-thaw rock is derived. According to the CT scanning test results of freeze-thaw sandstone under uniaxial compression, the theoretical and measured values of sandstone deformation localization band width under different freeze-thaw cycles are obtained. The derived formula is verified : the theoretical value is close to the measured value, which can better predict the rock deformation localization band width within 30 freeze-thaw cycles.

(2) The acoustic-thermal information multivariate monitoring test of the whole process of freeze-thaw sandstone uniaxial compression failure was carried out. According to the test results, the localization, evolution, macroscopic shear band formation and instability failure process of frozen-thawed sandstone were systematically and comprehensively analyzed from different acoustic thermal parameters such as acoustic emission energy, ringing count, cumulative ringing count, amplitude, maximum infrared radiation temperature, average infrared radiation temperature and infrared thermal image sequence diagram. The results show that with the increase of freeze-thaw cycles, the banded distribution characteristics of acoustic emission signal amplitude are weakened. The critical slowing phenomenon of frozen-thawed rock will occur under load. When the load is close to the yield point, the initial damage development and damage concentration expansion phenomenon appear in the rock sample. With the increase of freeze-thaw cycles, the ability of irreversible damage to return to the initial state is weakened, and the localization of rock deformation is enhanced. Under uniaxial compression load, the freeze-thaw sandstone experienced the process of initial microcrack ( pore ) compaction → microcrack regeneration → gradual penetration of cracks to produce deformation localization → formation and expansion of localization zone until the generation of macroscopic main cracks. The generation and evolution of the deformation localization zone of frozen-thawed rock is essentially a dynamic process of energy accumulation, dissipation and release.

(3) The acoustic emission three-dimensional positioning technology is used to accurately locate the deformation localization position, and the spatial failure characteristics of the freeze-thaw sandstone deformation localization are further studied. The results show that when the stress is 0.8~, a large number of acoustic emission events occur, and the distribution of event points gradually develops from disorder to order. The acoustic emission events nucleate into clusters, and the deformation localization occurs inside the rock. In the post-peak stage, many micro-cracks extend and converge to form multiple localized shear bands, and the localized bands expand outward and finally form macroscopic main cracks. At this time, a large number of high-energy event points appear inside the frozen-thawed rock sample. The failure of freeze-thaw rock is the result of the combined action of multiple internal deformation localization zones. The formation of rock deformation localization zone is a gradual cumulative process. The deformation localization zone of freeze-thaw rock is first formed in the middle of rock. The initial damage location is an important factor affecting the formation location of localization zone and rock failure mode.

(4) Based on the results of acoustic-thermal multivariate monitoring test of freeze-thaw sandstone under uniaxial compression, four acoustic-thermal analysis indexes for quantitatively describing the localized damage process of freeze-thaw sandstone are proposed : autocorrelation coefficient, coefficient of variation, time entropy and space entropy. The time characteristics of localized damage in the loading failure process of freeze-thaw sandstone are revealed. The results show that the acoustic emission autocorrelation coefficient and the mutation point of the coefficient of variation can be used as the criterion for the formation time point of the rock deformation localization zone. The variation law of the time entropy and the space entropy curve reflects the rock deformation localization stage. The localized failure time of sandstone is advanced with the increase of freeze-thaw times.

(5) The acoustic-thermal combined index is proposed to analyze the localization time characteristics and structural characteristics of acoustic-thermal deformation of frozen-thawed rock. The time sequence relationship of sandstone deformation localization under different freeze-thaw times under compression load is : 30 freeze-thaw sandstone < 20 freeze-thaw sandstone < 10 freeze-thaw sandstone < 5 freeze-thaw sandstone < non-freeze-thaw sandstone. The degree of deformation localization is : non-freeze-thaw sandstone > 5 freeze-thaw sandstone > 10 freeze-thaw sandstone > 20 freeze-thaw sandstone > 30 freeze-thaw sandstone. The freeze-thaw cycle changes the size, quantity and distribution characteristics of pore structure in rock, which leads to the change of acoustic-thermal deformation localization characteristics during fracture process. Through the time sensitivity analysis of sandstone deformation localization phenomenon under different indexes of acoustic emission and thermal imaging, it is found that the cumulative ringing of acoustic emission is more sensitive to the localization of rock deformation than the event point. The autocorrelation coefficient is more advantageous for describing the sensitivity of rock deformation localization. The combined application of thermal imaging technology and acoustic emission technology to predict the localization of rock deformation in cold regions can improve the reliability of disaster precursor identification.

(6) Based on the cellular automata theory, a three-dimensional numerical calculation model of sandstone with initial damage is established by using the elastic-plastic cellular automata software CASrock. The numerical tests of uniaxial compression failure process of rock with different damage locations, damage sizes and damage spacing are completed. By analyzing the failure degree ( RFD ), equivalent plastic shear strain ( Epstn ), equivalent tensile strain ( Epttn ) and local energy release rate ( LERR ) of rock mass on the surface and inside of each group of samples, it is found that the sandstone with damage in the middle has the shortest failure time, the damage size has an important influence on the final failure mode of rock, and the damage spacing has a great influence on the damage propagation direction of sandstone.