青藏高原东部冻融作用下花岗岩力学性质弱化机理研究

花岗岩山体通常被认为是稳定性较好的地质体，但在青藏高原东部高寒高海拔山区，因冻融作用导致花岗岩体力学性质变差，崩塌、滑坡等地质灾害频发。针对青藏高原东部理塘和八宿地区的花岗岩开展了冻融循环力学试验，通过波速、核磁共振方法分析了岩石冻融过程中的损伤发展趋势。试验结果表明：岩石内部损伤程度随着冻融次数的增加而增加，岩石波速则随着冻融次数的增加而明显降低；从核磁共振T2弛豫时间分布的发展规律可以推断，天然条件下风化较严重的岩样经过冻融循环后裂隙尺寸范围进一步增大，而风化程度微小的岩石经过冻融后裂隙尺寸范围较为集中。对经过冻融循环后的岩样进行三轴压缩试验，结果表明岩石的单轴抗压强度和弹性模量随冻融次数增大而减小，而泊松比和内摩擦角没有表现出明显的变化规律。基于试验数据和理论分析，以八宿花岗岩为例，提出了冻融损伤本构模型，对不同围压和冻融循环次数条件下的岩石应力应变全过程进行模拟和预测。

Research on the Weakening Mechanism of the Mechanical Behavior for the Granite in the Eastern Qinghai-Tibet Plateau Under the Condition of Freezing-Thawing Cycles

The granite in the eastern Qinghai Tibet Plateau was tested by the freezing thawing cyclic testing, and the damage trend of rock during freezing and thawing was analyzed by the wave velocity testing and nuclear magnetic resonance (NMR). The testing results showed that as the number of freezing thawing cycles increased, the inner damage degree increased and the wave velocity decreased obviously. The T2 distribution and development of NMR implied that the range of the size of cracks in the more weathered rock samples became wider due to freezing thawing cycles, while the size of the cracks in the less weathered samples is more concentrative. The samples which were tested by freezing and thawing were then tested on triaxial testing apparatus. The testing results showed that the uniaxial compressive strength and the elastic modulus decreased as the number of freezing thawing cycles increased, but the Poissons ratio and internal friction angle varied randomly. Based on the testing data and theoretical analysis, a freezing thawing damage constitutive model was presented, which can be used for simulating and predicting the overall variation of stress and strain of rocks.