随着国家“一带一路”倡议的深入推进，“陆上丝绸之路新经济带”和“中巴经济走廊”沿线工程正在加紧建设。工程沿线多分布在高寒山区或多年冻土区，岩土体多处于冻结状态。冻结岩体的力学特性直接影响着工程的安全建设和稳定运营。由于冻结岩石中孔隙水/冰成分的复杂多变，以及冰所具备的压融效应，冻结岩石的力学特性仍需进一步系统研究。本文以冻结砂岩为研究对象，研究了不同初始饱和度下冻结砂岩的力学性质，基于PFC2D研究了冻结砂岩的细观破裂规律，基于电阻率变化探究了冻结岩石孔隙冰的压融效应及其影响。具体研究内容和结论如下：

（1）开展不同冻结温度和不同初始饱和度条件下冻结岩石强度特性与破坏过程的研究，进行不同初始饱和度下及不同负温下冻结岩石的单轴压缩试验和巴西劈裂试验，根据单轴压缩试验得出的应力-应变曲线，结合单轴压缩过程中的声学信号变化以及试样表面变形，分析冻结岩石的破坏过程。研究发现冻结岩石的单轴抗压强度随着饱和度的增加表现为三个阶段变化，界限温度为-4℃和-12℃，随着初始饱和度的增大也呈三阶段变化；冻结作用使得饱和岩石振铃计数的突增从峰值应力处转变至峰后阶段，而在初始饱和度大于1.8%时也出现了同样的变化；岩石的破坏模式在冻结温度大于-4℃呈劈裂破坏，在冻结温度小于-4℃呈剪切破坏，而初始饱和度增大至3.63%时，其最终破坏模式与冻结温度所造成影响的结果类似。

（2）基于颗粒流离散元理论，采用PFC2D计算分析程序，选取适合本试验的内置接触本构模型，通过进行不同参数的敏感性分析模拟试验，确定各细观参数的变化规律，接着根据室内试验测得试样的宏观参数，对试样进行细观参数的标定，得到与之相互对应的细观参数，通过对裂纹数目、起裂应力水平、粘结数目等的定量分析，从细观层面解释冻结温度对岩石力学特性的影响过程。发现冻结岩石的力学特性主要取决于冰的强度和冰-岩界面强度。究其原因应是冰自身强度及冰-岩界面强度对温度的敏感性所致。孔隙冰充填空隙空间，在外荷载作用下可起到支撑孔隙和粘结孔隙的作用。在-4 ℃至-2 ℃之间，冰颗粒之间粘结强度和冰-矿物粘结强度均迅速衰减，导致冰的支撑和粘结作用弱化，是该温度区间力学性质快速弱化的本质原因。

（3）进行不同初始饱和度和负温条件下冻结岩石的核磁共振试验，分析其内部孔隙冰的分布特征。发现饱和岩石中自由水和毛细水最先发生冻结，随后只有吸附水发生冻结；初始饱和度的增加导致孔隙水的冻结过程由两阶段转为三阶段变化。不同饱和度岩石冻结过程中未冻水含量的变化存在显著差异。开展不同初始饱和度冻和不同负温下冻结岩石单轴压缩过程中电阻变化的试验，分析不同变形阶段的电阻变化幅度，通过对比常温和低温条件下不同含水状态岩石单轴压缩过程中电阻的变化，发现饱和冻结岩石微裂纹压密阶段发生了显著的压融效应，随着冻结温度的降低，微裂纹压密阶段的平均电阻率呈先迅速增加后基本保持不变的趋势。

（4）孔隙水在冻结过程中，其中的冰-水相变平衡由压力和温度共同决定，冻结岩石的破坏过程受孔隙冰的压融效应影响，结合压缩过程中的电阻变化幅度，从应力-应变曲线的初始压密阶段、弹性变形阶段、微裂纹扩展阶段对孔隙冰压融效应对力学性质的影响进行分析。在孔隙压密阶段，大小孔隙中的冰对岩石骨架具有支撑作用，随着压力的增大，电阻率出现大幅度的减小，小孔隙中的冰被压融从而形成孔隙水。弹性变形阶段，孔隙中的冰与部分较大孔径的微裂隙中的冰与岩石骨架共同发生弹性变形，部分次小孔隙中的冰被压融形成孔隙水。微裂纹扩展阶段，小孔隙中的冰此时基本完全被压融，大孔隙中的冰对岩石骨架的胶结作用和充填作用使得岩石中的微裂纹扩展缓慢。

With the deepening of the national "the Belt and Road" initiative, the construction of projects along the "Land Silk Road New Economic Belt" and the "China Pakistan Economic Corridor" is accelerating. The engineering line is mostly distributed in high-altitude mountainous areas or permafrost regions, and the rock and soil are mostly in a frozen state. The mechanical properties of frozen rock masses directly affect the safe construction and stable operation of engineering. Due to the complex and variable composition of pore water/ice in frozen rocks, as well as the pressure melting effect of ice, the mechanical properties of frozen rocks still need further systematic research. This article takes frozen sandstone as the research object, studies the mechanical properties of frozen sandstone under different initial saturation levels, studies the micro fracture law of frozen sandstone based on PFC2D, and explores the pressure melting effect and its influence of frozen rock pore ice based on changes in electrical resistivity. The specific research content and conclusions are as follows:

(1) Conduct research on the strength characteristics and failure process of frozen rocks under different freezing temperatures and initial moisture contents. Conduct uniaxial compression tests and Brazilian splitting tests on frozen rocks under different initial moisture contents and negative temperatures. Based on the stress-strain curve obtained from uniaxial compression tests, analyze the failure process of frozen rocks by combining the acoustic signal changes during uniaxial compression and the surface deformation of the specimen. Research has found that the uniaxial compressive strength of frozen rocks varies in three stages with increasing moisture content, with boundary temperatures of -4 ℃ and -12 ℃. It also shows a three-stage variation with increasing initial moisture content; The freezing effect causes a sudden increase in the ringing count of saturated rocks from the peak stress to the post peak stage, and the same change occurs when the initial moisture content is greater than 1.8%; The failure mode of rocks exhibits splitting failure when the freezing temperature is above -4 ℃, and shear failure when the freezing temperature is below -4 ℃. When the initial moisture content increases to 3.63%, the final failure mode is similar to the effect of freezing temperature.

(2) Based on the particle flow dispersion element theory and using the PFC2D calculation and analysis program, a built-in contact constitutive model suitable for this experiment was selected. Sensitivity analysis and simulation experiments were conducted on different parameters to determine the variation patterns of each microscopic parameter. Then, based on the macroscopic parameters measured in indoor experiments, the microscopic parameters of the sample were calibrated to obtain the corresponding microscopic parameters. Through quantitative analysis of crack number, initiation stress level, bonding number, etc., the influence of freezing temperature on rock mechanical properties was explained from the microscopic level. The mechanical properties of frozen rocks mainly depend on the strength of ice and the strength of the ice rock interface. The reason for this should be the sensitivity of the strength of the ice itself and the strength of the ice rock interface to temperature. Pore ice filling voids can support and bond pores under external loads. Between -4 ℃ and -2 ℃, the bonding strength between ice particles and between ice and minerals rapidly decreases, leading to a weakening of the support and bonding effect of ice, which is the essential reason for the rapid weakening of mechanical properties in this temperature range.

(3) Conduct nuclear magnetic resonance tests on frozen rocks under different initial water content and negative temperature conditions, and analyze the distribution characteristics of internal pore ice. It was found that free water and capillary water in saturated rocks first freeze, followed by only adsorbed water freezing; The increase in initial moisture content leads to a three-stage change in the freezing process of pore water from two stages. There are significant differences in the variation of unfrozen water content during the freezing process of rocks with different water contents. Conduct experiments on the changes in electrical resistance during uniaxial compression of frozen rocks with different initial water contents and negative temperatures, analyze the amplitude of electrical resistance changes during different deformation stages, and compare the changes in electrical resistance during uniaxial compression of rocks with different water contents under normal temperature and low temperature conditions. It is found that significant compression and thawing effects occur during the microcrack compaction stage of saturated frozen rocks. As the freezing temperature decreases, the average electrical resistance during the microcrack compaction stage first increases rapidly and then remains basically unchanged.

(4) During the freezing process of pore water, the ice water phase equilibrium is determined by both pressure and temperature. The failure process of frozen rocks is influenced by the pressure melting effect of pore ice. Combined with the amplitude of electrical resistance changes during compression, the influence of pore ice pressure melting effect on mechanical properties is analyzed from the initial compaction stage, elastic deformation stage, and microcrack propagation stage of the stress-strain curve. During the pore compaction stage, the ice in the small and large pores supports the rock skeleton. As the pressure increases, the electrical resistivity decreases significantly, and the ice in the small pores is melted and compressed to form pore water. In the stage of elastic deformation, the ice in the pores and the ice in some larger micro cracks and rock skeletons undergo elastic deformation together, and the ice in some sub small pores is compressed and melted to form pore water. In the stage of microcrack propagation, the ice in the small pores is basically completely melted by compression, while the ice in the large pores has a slow expansion of microcracks in the rock due to its cementation and filling effect on the rock skeleton.