在寒冷地区，由于循环冻融和长时间载荷的共同作用，岩体会随着时间的推移而失稳破坏。为探讨寒区恶劣环境对工程岩体长期稳定性的影响，本文通过加卸载蠕变试验和核磁共振检测技术，对陕北某工程岩体的红砂岩进行了研究，重点对蠕变过程中宏观力学指标和细观参数的变化进行定量分析，并结合岩石蠕变的非线性特性，构建了一种非线性黏弹塑性蠕变模型，该模型同时考虑了冻融和蠕变损伤的影响。以下是本文的主要研究内容：

对不同冻融红砂岩进行了核磁共振检测及单轴压缩试验，探究了循环冻融对红砂岩细观孔隙结构演化及力学特性的影响。随着红砂岩受冻融损伤程度的增强，压实阶段其应力-应变曲线延长，凹弧逐渐明显；冻融红砂岩的峰值应变、泊松比逐渐增大，单轴强度、弹性模量逐渐降低，岩样表面破裂程度愈发严重。随着冻融次数的增加，红砂岩孔隙分布由小孔占比增长占主导转为大孔占比增长占主导，说明冻融红砂岩孔隙结构在冻融前期主要表现为微小孔隙的萌生，冻融后期主要表现为微裂纹融合和扩展。引入分形理论来描述冻融红砂岩孔隙结构的复杂程度，冻融红砂岩大孔分维D₂与总孔分维D_T呈高度正相关，其孔隙结构的复杂程度主要受大孔孔隙结构的影响。

利用核磁共振技术监测蠕变试验过程中冻融红砂岩的蠕变行为，对试验得到的宏观力学指标及细观参数进行了定量分析。除冻融60次红砂岩在初始蠕变阶段破坏外，其余红砂岩均表现出完整蠕变破坏特征，并且冻融次数越多，加速蠕变时间越短，应变变化更为迅速。当应力水平较低时，冻融红砂岩的稳态蠕变速率、塑性应变、纵波波速、孔隙度、T₂谱面积以及总孔分维D_T等宏、细观参数均随应力水平上升而缓慢增长；当达到高应力水平（0.6σ_ucs）时，上述参数均突然大幅增长，即红砂岩宏观和细观蠕变特征在高应力水平下受冻融作用的影响更为显著。蠕变过程中，D₂与应力水平呈正相关，且D_T与孔隙度可用正线性函数描述；孔隙结构复杂程度仅在孔隙度较大时才对冻融岩石蠕变特性产生明显影响，分形维数越大，蠕应变量和蠕变速率在相同孔隙度下越高。

借鉴建立非线性蠕变模型的常规方法，结合冻融红砂加卸载蠕变试验的结果，引入对Abel黏壶进行改进而来的变系数Abel黏壶作为冻融损伤黏性元件，建立了考虑冻融损伤的非线性黏弹塑性蠕变模型。通过比较试验曲线与模型拟合曲线来验证模型的准确性，发现该模型能准确反映不同冻融红砂岩在不同加载应力水平下的蠕变状态。

In cold regions, rock mass can be damaged over time due to a combination of freeze-thaw cycles and prolonged loading. In order to explore the influence of the harsh environment in cold regions on the long-term stability of engineering rock mass, the red sandstone of an engineering rock mass in northern Shaanxi was studied through the loading and unloading creep test and nuclear magnetic resonance detection technology, focusing on the macroscopic mechanical properties of the creep process. Quantitative analysis was carried out on the changes of indexes and mesoscopic parameters, and combined with the nonlinear characteristics of rock creep, a viscoelastic-plastic creep model was constructed, which considered the effects of freeze-thaw and creep damage at the same time. The following is the main research content of this paper:

NMR detection and uniaxial compression tests were carried out on different freeze-thaw red sandstones, and the effects of cyclic freeze-thaw cycles on the evolution of mesoscopic pore structures and the deterioration of mechanical properties of red sandstones were explored. With the increase of freeze-thaw damage of red sandstone, the stress-strain curve of the compaction stage is prolonged, and the concave arc increases; the peak strain and Poisson's ratio of freeze-thaw red sandstone gradually increase, and the uniaxial strength and elastic modulus gradually decrease , the degree of rock sample surface cracking becomes more and more serious. With the increase of freeze-thaw times, the pore distribution of red sandstone changes from the growth of small pores to the growth of large pores, which indicates that the pore structure of freeze-thaw red sandstone is mainly represented by the initiation of tiny pores in the early freeze-thaw period. The later stage of melting is mainly manifested as the fusion and expansion of microcracks. The fractal theory is introduced to describe the complexity of the pore structure of the freeze-thaw red sandstone. The macropore fractal dimension D₂ of the freeze-thaw red sandstone is highly positively correlated with the total pore fractal dimension D_T, and the complexity of the pore structure is mainly affected by the macropore structure existing therein Influence.

The creep behavior of the freeze-thaw red sandstone during the creep test was monitored by nuclear magnetic resonance technology, and the evolution of the macroscopic mechanical indexes and mesoscopic parameters obtained from the test was quantitatively analyzed. Except that the red sandstone was destroyed in the initial creep stage after 60 times of freezing and thawing, the others all showed complete creep failure characteristics, and the more freezing and thawing times, the shorter the accelerated creep time and the more rapid the strain change. When the stress level is low, the steady-state creep rate, plastic strain, P-wave velocity, porosity, T₂ spectral area, and total pore fractal dimension D_T of the freeze-thaw red sandstone all increase slowly with the increase of the stress level. ; When the high stress level (0.6σ_ucs) is reached, the above parameters all increase suddenly, that is, the macroscopic and mesoscopic creep characteristics of red sandstone are more significantly affected by freeze-thaw at high stress levels. During the creep process, D₂ is positively correlated with the stress level, and D_T and porosity can be described by a positive linear function; the complexity of the pore structure has a significant impact on the creep characteristics of freeze-thaw rocks only when the porosity is large. The larger the value, the higher the creep strain and creep rate at the same porosity.

Referring to the conventional method of establishing a nonlinear creep model, combined with the results of the freeze-thaw red sand loading and unloading creep test, the variable coefficient Abel sticky pot improved by the Abel sticky pot was introduced as the viscous element of freeze-thaw damage, and the A nonlinear viscoelastic-plastic creep model for freeze-thaw damage. Comparing the fitting curve between the experimental data and the model, it is found that it can accurately reflect the creep state of different freeze-thaw red sandstone under different loading stress levels, which verifies the accuracy of the model.