传统蠕变模型较难表征岩石的完整蠕变行为。为揭示花岗岩卸荷蠕变力学特性，以某抽水蓄能电站高钾钙碱性I型花岗岩为研究对象，取样开展恒轴压卸围压应力路径下的三轴卸荷蠕变试验，分析了卸荷过程中花岗岩蠕变应变特征及岩石损伤演化规律，基于分数阶微积分理论构建了能够精确描述花岗岩蠕变全过程的变系数非定分数阶卸荷蠕变损伤模型，并扩展到三维应力状态。结果表明：在三轴卸荷蠕变试验中，随着围压的减小，试样每一级的轴向蠕变总量不断增大，轴向总应变以瞬时弹性应变为主，岩石呈现出应变软化特性，破坏时为脆性破坏；利用变系数非定分数阶卸荷蠕变损伤模型对三轴卸荷蠕变试验数据进行了参数辨识和拟合，拟合结果表明该模型能够较好的描述燕山期高钾钙碱性I型花岗岩的蠕变损伤演化特性。研究成果可为类似地区地下洞室围岩长期稳定性研究及支护方案设计提供试验依据和理论指导。

The traditional creep model is difficult to characterize the complete creep behavior of rock. In order to reveal the unloading creep mechanical properties of granite, the high-potassium calc-alkaline I-type granite of a pumped storage power station was taken as the research object, and the triaxial unloading creep test under the constant axial pressure unloading confining pressure stress path was carried out. The creep strain characteristics and rock damage evolution law of granite during unloading process were analyzed. Based on the fractional calculus theory, a variable coefficient non-definite fractional unloading creep damage model which can accurately describe the whole process of granite creep was constructed and extended to three-dimensional stress state. The results show that in the triaxial unloading creep test, with the decrease of confining pressure, the total axial creep of each stage of the sample increases continuously, and the total axial strain is dominated by instantaneous elastic strain. The rock exhibits strain softening characteristics and is brittle failure when destroyed. The parameter identification and fitting of the triaxial unloading creep test data were carried out by using the variable coefficient unsteady fractional unloading creep damage model. The fitting results show that the model can better describe the creep damage evolution characteristics of the high potassium calc-alkaline I-type granite in Yanshan period. The research results can provide experimental basis and theoretical guidance for the long-term stability research and support scheme design of underground caverns in similar areas.