在岩土工程施工及其运营阶段，经常会遇到周期荷载的作用，这些荷载为不同频率、幅值及作用历时的循环载荷，其变形规律、裂纹扩展速度效应、破坏特征等与静荷载作用下有很大不同，破坏具有突然性，事先没有预兆，破坏时的应力也远低于材料的静强度。本项目拟在前期工作的基础上通过现场调研、理论研究、试验研究、数值模拟和应用研究，探讨周期载荷条件下岩石疲劳裂纹萌生、亚临界时效扩展规律、能量释放规律、裂纹稳定扩展及快速扩展条件、破坏特征等内容；查找和量化损伤断裂过程中岩石断裂表面上的细观损伤及其特性，确定周期载荷作用下岩石断裂表面的宏观、细观及微观多尺度参数与岩石疲劳裂纹亚临界扩展的关系及其弱化规律；建立从宏观到细观再到微观的多层次相互嵌套连接的损伤断裂模型；确定周期载荷作用下裂纹亚临界扩展的极限时间，预测周期载荷下岩土工程的破坏条件及疲劳寿命。

Cycle loads often appear in stage of building and using of the geotechnical engineering. They are different from the static loads in deformation laws, crack propagation speed effect and failure characteristics because of the influence of frequency, amplitude and action time. The fatigue failure is sudden and no warning. The failure stress is much lower than the strength of the material under static load. In this project，some researches, such as fatigue crack initiation, fatigue subcritical crack growth, law of energy release, conditions of crack growth steadily and rapidly, failure characteristics and so on, are discussed under the cycle loads by site investigation, theoretical research, experimental study ,numerical simulation and application on the basis of previous work. The meso-scale damage and characteristics are located and quantified on the fracture surface of rock in damage fracture process under cycle load. The relations and weakening rules between multi-scale parameters on the fracture surface and fatigue subcritical crack growth are obtained under cycle load. The multi-scale damage fracture model from macro-scale to meso-scale and micro-scale is established. The limit time of subcritical crack propagation is estimated under cycle loading, which the damage condition and fatigue life of geotechnical engineering are predicted .