在季冻区的铁路、公路路堑及露天矿山等的边坡常经受冻融与周期荷载的共同作用，引发边坡滑坡、落石等地质灾害，研究两者耦合作用下季冻区裂隙岩体的宏细观损伤破坏机理对季冻区岩体工程的安全建设、地质灾害预报与防治及其长期稳定性评价具有重要的理论意义和工程应用价值。主要研究结论如下：

（1）研究了不同冻融循环次数下不同岩桥长度双裂隙花岗岩的三轴压缩宏细观损伤破坏规律，结果表明：随着冻融循环次数的增加，花岗岩的裂纹逐渐扩展并加深；花岗岩的饱和质量非线性减小，饱和波速持续降低；花岗岩的泊松比、轴向与径向的峰值应变增大，其余力学参数均降低；花岗岩声发射计数的峰值与累计值非线性增大；冻融后花岗岩的薄弱面处易在单轴作用下产生剪切裂纹，破裂面变得更复杂；花岗岩的T₂（核磁共振测试中的总弛豫时间）谱总面积逐渐增加，微孔和小孔占比减少，中孔和大孔占比增多，单轴压缩破坏后其孔径从中孔为主变为大孔为主，且超大孔增加。随着岩桥长度的增加，双裂隙花岗岩的泊松比非线性减小，其余力学参数非线性增大；双裂隙花岗岩声发射计数的峰值与累计值非线性减小；双裂隙花岗岩破坏后T₂谱总面积增加率变大。

（2）研究了不同冻融次数下双裂隙花岗岩的三轴压缩疲劳宏观力学特性、声发射特性以及细观孔隙演化特征，结果表明：随着冻融次数的增加，双裂隙花岗岩的疲劳寿命降低；双裂隙花岗岩在“沉寂期”内的声发射计数增多，声发射的最大源幅值变小，其大尺度破裂减少，声发射事件的数量非线性减少；双裂隙花岗岩破坏后的T₂谱总面积变化率非线性降低，周期荷载破坏后岩样中占比最大的孔径由中孔变为大孔。相比单调加载，周期荷载作用下双裂隙花岗岩的破坏更具突然性，并且伴随大量颗粒以及块体喷射，岩样的裂纹贯通更明显，破裂面更复杂。

（3）研究了冻融循环作用下不同岩桥长度双裂隙花岗岩的三轴压缩疲劳宏观力学特性、声发射特性以及细观孔隙演化特征，结果表明：随着岩桥长度的增加，双裂隙花岗岩的疲劳寿命逐渐增大，声发射计数累计值增大，声发射事件的最大源幅值增大，三轴压缩下声发射事件的数量增加；周期荷载下双裂隙花岗岩的破坏模式从拉剪混合破坏转变成以拉伸破坏为主，双裂隙花岗岩的破坏后T₂谱总面积变化率增大，周期荷载破坏后岩样超大孔占比的增长率也增加。

（4）研究了冻融循环与不同应力振幅作用下双裂隙花岗岩的三轴压缩疲劳宏观力学特性、声发射特性以及细观孔隙演化特征，结果表明：随着应力振幅的增加，双裂隙花岗岩的疲劳寿命逐渐减小，周期荷载“沉寂期”内的声发射计数峰值及累计值均增大，单轴压缩下由初始上升角RA与平均频率AF表征的剪切裂纹比例升高，周期荷载阶段的b值增大，声发射事件的数量非线性减小，声发射事件的最大源幅值变小；单轴压缩周期荷载下双裂隙花岗岩的破坏模式从拉伸破坏转变成拉剪混合破坏，双裂隙花岗岩破坏后的T₂谱总面积变化率减小，经周期荷载试验破坏后的超大孔占比减小。

（5）冻融循环的冻胀力作用导致花岗岩细观孔（裂）隙的尺寸和数量逐渐增加，预制雁行双裂隙的存在导致花岗岩的冻融损伤更严重，在宏观上表现为抗压强度的降低，多次冻融后花岗岩产生大量新裂纹，受单（三）轴压缩后新裂纹不仅从预制裂隙尖端处萌生而且沿着冻融产生的宏观裂纹继续扩展，所以冻融与预制双裂隙的耦合作用降低了花岗岩的力学性能。预制双裂隙之间岩桥区的增大，使得裂纹能够在岩桥区更自由地扩展，所以导致较长岩桥长度双裂隙花岗岩的破坏后孔隙增长率更大。随着振幅应力比λ的增加，双裂隙花岗岩的疲劳寿命减小，内部微裂隙扩展发育减缓，能够储存的含H流体也越少，最终表现为核磁共振（NMR）T₂谱面积变化率减小。

（6）依据断裂力学应变能理论推导出宏观双裂隙对花岗岩造成的损伤量，结合孔隙率表征的冻融损伤以及微元强度服从Weibull分布的受荷损伤量，耦合成包含宏观裂隙损伤、冻融损伤与荷载损伤的双裂隙花岗岩总损伤量。将基于不可逆轴向应变的变形模量演化模型与总损伤变量构建为冻融与单轴压缩周期荷载下裂隙花岗岩疲劳变形本构模型。根据单轴压缩周期荷载作用下双裂隙花岗岩的试验数据对疲劳变形本构模型进行验证，理论曲线与试验结果基本吻合。

The slopes of railways, highways and open-pit mines in the seasonal frozen area are often subjected to the combined action of freeze-thaw and cyclic loading, causing geological disasters such as slope landslides and rockfalls. It is of great theoretical significance and engineering application value to study the macro-meso damage and failure mechanism of fissured rock mass in the seasonal frozen area under the coupling effect of the two influences for the safety construction, geological disaster prediction and prevention and long-term stability evaluation of rock mass engineering in the seasonal frozen area. The main conclusions are as follows:

(1) The macro-meso damage law of triaxial compression of double-fissured granite with different rock bridge lengths under different freeze-thaw cycles was studied. The results show that with the increase in freeze-thaw cycles, the cracks of granite gradually expand and deepen. The saturated mass of granite decreases nonlinearly, and the saturated wave velocity decreases continuously. The Poisson's ratio, axial and radial peak strains of granite increase, and the other mechanical parameters decrease. The peak value and cumulative value of acoustic emission count of granite increase nonlinearly; after freezing and thawing, the weak surface of granite is easy to produce shear cracks under uniaxial action, and the fracture surface becomes more complex. The total area of T₂ ( total relaxation time in nuclear magnetic resonance test ) spectrum of granite gradually increased, the proportion of micropores and small pores decreased, and the proportion of mesopores and macropores increased. After uniaxial compression failure, the pore size of granite changed from mesopores to macropores, and the supermacropores increased. With the increase in rock bridge length, the Poisson's ratio of double-fissured granite decreases nonlinearly, and the other mechanical parameters increase nonlinearly. The peak value and cumulative value of the acoustic emission count of the double-fissured granite decrease nonlinearly; the increase rate of the total area of T₂ spectrum becomes larger after the destruction of the double-fissured granite.

(2) The triaxial compression fatigue macroscopic mechanical properties, acoustic emission characteristics and meso-pore evolution characteristics of double-fissured granite under different freeze-thaw cycles were studied. The results show that the fatigue life of double-fissured granite decreases with the increase in freeze-thaw cycles. The acoustic emission count of double-fissured granite increases in the 'silence period', the maximum source amplitude of acoustic emission decreases, the large-scale fracture decreases, and the number of acoustic emission events decreases nonlinearly. The change rate of the total area of T₂ spectrum after the failure of the double-fissured granite decreases nonlinearly, and the pore size with the largest proportion in the rock sample after the cyclic load failure changes from mesopore to macropore. Compared with monotonic loading, the failure of double-fissured granite under cyclic loading is more sudden, and with a large number of particles and block jets, the crack penetration of rock samples is more obvious and the fracture surface is more complex.

(3) The triaxial compression fatigue macroscopic mechanical properties, acoustic emission characteristics and mesoscopic pore evolution characteristics of double-fissured granite with different rock bridge lengths under freeze-thaw cycles were studied. The results show that with the increase of rock bridge length, the fatigue life of double-fissured granite gradually increases, the cumulative value of acoustic emission count increases, the maximum source amplitude of acoustic emission events increases, and the number of acoustic emission events under triaxial compression increases. The failure mode of double-fissured granite under cyclic loading changes from tensile-shear mixed failure to tensile failure. The change rate of the total area of T₂ spectrum after the failure of the double-fissured granite increases, and the growth rate of the proportion of super-large pores in rock samples after cyclic loading failure also increases.

(4) The macro-mechanical properties, acoustic emission characteristics and meso-pore evolution characteristics of triaxial compression fatigue of double-fissured granite under freeze-thaw cycles and different stress amplitudes are studied. The results show that with the increase of stress amplitude, the fatigue life of double-fissured granite decreases gradually, and the peak value and cumulative value of acoustic emission count in the 'quiet period' of cyclic loading increase. Under uniaxial compression, the proportion of shear cracks characterized by initial rising angle RA and average frequency AF increases, the b value in the cyclic load stage increases, the number of acoustic emission events decreases nonlinearly, and the maximum source amplitude of acoustic emission events decreases. The failure mode of double-fissured granite under uniaxial compression cyclic load changes from tensile failure to tensile-shear mixed failure. The total area change rate of T₂ spectrum after the failure of double-fissured granite decreases, and the proportion of super-large pores after the failure of cyclic load test decreases.

(5) The frost heaving force of the freeze-thaw cycle leads to the gradual increase of the size and number of meso-pores ( cracks ) in granite. The existence of the prefabricated double echelon fissures leads to more serious freeze-thaw damage of granite, which is manifested as the decrease of compressive strength on the macro level. After multiple freeze-thaw cycles, a large number of new cracks are generated in granite. After uniaxial ( triaxial ) compression, new cracks not only initiate from the tip of prefabricated fissures but also continue to expand along the macro cracks generated by freeze-thaw. Therefore, the coupling effect of freeze-thaw and prefabricated double fissures reduces the mechanical properties of granite. The increase of the rock bridge area between the prefabricated double fissures makes the cracks expand more freely in the rock bridge area, so that the pore growth rate of the double-fissured granite with longer rock bridge length is larger after the failure. With the increase in amplitude stress ratio λ, the fatigue life of double-fissured granite decreases, the expansion and development of internal micro-cracks slows down, and the less H-bearing fluid can be stored. Finally, the change rate of NMR T₂ spectrum area decreases.

(6) According to the strain energy theory of fracture mechanics, the damage amount of granite caused by macroscopic double fissures is derived. Combined with the freeze-thaw damage characterized by porosity and the load damage of micro-element strength obeying Weibull distribution, the total damage of double-fissured granite including macroscopic fissure damage, freeze-thaw damage and load damage is coupled. The evolution model of deformation modulus based on irreversible axial strain and the total damage variable are constructed as the fatigue deformation constitutive model of fissured granite under freeze-thaw and uniaxial compression cyclic loading. The fatigue deformation constitutive model is verified according to the experimental data of double fissured granite under uniaxial compression cyclic loading. The theoretical curve is basically consistent with the experimental results.