寒区岩体工程在遭受冻融灾害的同时，往往还受到施工扰动与交通荷载的影响，开展冻融与周期荷载耦合作用下裂隙岩体的损伤破坏机制研究具有重要意义。本文利用低强度、低密度、高孔隙率的裂隙红砂岩岩样为研究对象，采用试验研究、理论分析和数值模拟相结合的研究方法对冻融损伤与周期荷载疲劳损伤耦合作用下岩样的强度劣化与裂纹演化规律进行研究，主要工作和结论是：

（1）完成了冻融循环试验，并对不同冻融次数的岩样进行了波速与质量的测定。随着冻融次数的增加，岩样的损伤程度增大，表面裂纹往内部发展，预制裂隙尖端处拉应力集中；岩样饱水质量随冻融次数的增加所表现的总体趋势为下降，而岩样纵波波速与冻融循环次数近似呈线性反比关系。

（2）完成了不同冻融循环次数作用下三轴压缩试验，同步完成了声波及声发射测试试验。随着冻融次数的增加，岩样的物理力学参数与特征应力降低，裂纹更易发生萌生与扩展，预制裂隙尖端处更频繁的出现次生裂纹，扩容现象剧烈，随着围压的增加，岩样力学性能强化，破裂面的贯通模式以张拉劈裂破坏为主变为以剪切张拉复合型破坏为主。对比分析了波速-时间曲线与应力-时间曲线，其曲线特征说明波速能够用于评价寒区工程岩体力学性质。得到了岩样裂纹在开裂、扩展时的声发射计数响应情况，说明了振铃计数可作为损伤基准量来对双裂隙红砂岩损伤情况进行分析。

（3）完成了不同冻融循环次数作用下三轴周期荷载试验，并完成了周期荷载试验全过程的声波及声发射测试试验。随着冻融次数的增加，岩样的疲劳极限降低，破坏时裂纹发展多且复杂，破坏程度更严重；高围压能够提高岩样内部的各向同性，疲劳极限升高，较压缩试验的破坏形态差异减小。发现了声波波速随应力循环缓慢上升后突然下降，可作为岩石发生破坏的征兆。分析了周期荷载作用下声发射累计振铃计数曲线走势，可作为岩样疲劳损伤状态的判断依据。

（4）完成了双裂隙红砂岩细观损伤核磁共振试验。随着冻融循环次数的增加，T₂谱曲线右移，T₂谱面积增加；压缩破坏前后谱面积测试结果说明谱面积变化受岩样的孔隙结构与破坏程度影响较大，冻融损伤易提高岩样的破坏程度；周期荷载作用破坏后T₂谱面积较压缩破坏增幅更大，从细观特征变化验证了岩样受周期荷载作用裂纹扩展更加充分，而冻融循环与周期荷载的耦合作用将增大岩样的内部损伤。

（5）基于变阶分数阶蠕变本构模型，用循环次数与频率换算代替蠕变时间，定义了冻融损伤变量后，建立了冻融及周期荷载下双裂隙红砂岩疲劳本构模型，并完成了三维推广与模型适用性验证。

（6）利用颗粒流程序完成了双裂隙红砂岩岩样三轴压缩及周期荷载试验的数值模拟。模拟结果曲线及裂纹演化模拟结果与实际试验结果基本对应，但在冻融次数较多时，改变岩样细观参数获得的模拟结果与实际试验情况有一定的偏差。数值模拟结果揭示了岩样三轴压缩及周期荷载试验中的裂纹扩展规律以及各阶段的破坏特征，与试验结果形成相互印证。

Rock mass engineering in cold regions is often affected by construction disturbance and traffic load while suffering freeze-thaw disasters. It is of great significance to study the damage and failure mechanism of fractured rock mass under the coupling effect of freeze-thaw and periodic load. In this paper, the fractured red sandstone rock samples with low strength, low density and high porosity are used as the research object. The strength degradation and crack evolution of rock samples under the coupling of freeze-thaw damage and periodic load fatigue damage are studied by experimental research, theoretical analysis and numerical simulation. The main work and conclusions are as follows :  

(1) Completed the freeze-thaw cycle test, and measured the wave velocity and quality of rock samples with different freeze-thaw cycles. With the increase of freeze-thaw cycles, the damage degree of rock samples increases, the surface cracks develop to the interior, and the tensile stress at the tip of the prefabricated crack is concentrated. The saturation quality of rock samples decreases with the increase of freeze-thaw cycles, and the longitudinal wave velocity of rock samples is approximately linearly inversely proportional to the number of freeze-thaw cycles.

(2) The triaxial compression test under different freeze-thaw cycles was completed, and the acoustic wave and acoustic emission test were completed simultaneously. With the increase of freeze-thaw cycles, the physical and mechanical parameters and characteristic stress of rock samples decrease, and the cracks are more prone to initiation and propagation. Secondary cracks appear more frequently at the tip of prefabricated cracks, and the expansion phenomenon is severe. With the increase of confining pressure, the mechanical properties of rock samples are strengthened. The penetration mode of fracture surface is changed from tensile splitting failure to shear tensile composite failure. The wave velocity-time curve and stress-time curve are compared and analyzed. The curve characteristics show that the wave velocity can be used to evaluate the mechanical properties of engineering rock mass in cold regions. The acoustic emission count response of rock sample crack in cracking and propagation is obtained, which shows that ringing count can be used as a damage benchmark to analyze the damage of double fractured red sandstone.

(3) Completed the triaxial periodic load test under the action of different freezing-thawing cycles, and completed the acoustic and acoustic emission test in the whole process of the periodic load test.  With the increase of freezing-thawing times, the fatigue limit of rock samples decreases, and the crack development is more complicated and the damage degree is more serious.  High confining pressure can improve the isotropy of rock sample, increase the fatigue limit, and reduce the failure mode difference compared with compression test.  It is found that the acoustic wave velocity rises slowly with the stress cycle and then drops suddenly, which can be used as a sign of rock failure.  The trend of cumulative acoustic emission ringing count curve under cyclic loading is analyzed, which can be used as the basis for judging the fatigue damage state of rock samples.    

(4) Completed the mesoscopic damage NUCLEAR magnetic resonance test of red sandstone with double fissures.  With the increase of the number of freezing-thawing cycles, T₂ spectrum curve moves to the right and T₂ spectrum area increases.  The spectral area test results before and after compression failure show that the spectral area change is greatly affected by the pore structure and damage degree of rock samples, and the damage degree of rock samples is easily increased by freeze-thaw damage.  The increase of T₂ spectral area after periodic loading is larger than that after compression failure, which verifies that the crack propagation of rock samples under periodic loading is more sufficient from the change of microscopic characteristics, and the coupling effect of freezing-thawing cycle and periodic load will increase the internal damage of rock samples.  

(5) Based on the variable-order fractional creep constitutive model, the creep time was replaced by the number of cycles and frequency conversion. After defining the freezing-thawing damage variables, the fatigue constitutive model of red sandstone with double cracks under freezing-thawing and periodic loads was established, and the three-dimensional extension and applicability verification of the model were completed.  

(6) The numerical simulation of triaxial compression and cyclic loading test of red sandstone samples with double fractures was completed by using particle flow program. The simulation curve and crack evolution simulation results are basically corresponding to the actual test results, but when the number of freeze-thaw cycles is large, the simulation results obtained by changing the microscopic parameters of rock samples have certain deviation from the actual test results. The numerical simulation results reveal the crack propagation law and the failure characteristics of each stage in the triaxial compression and periodic load test of rock samples, which are mutually verified with the test results.

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