不同加卸载条件下孟底沟水电站花岗岩蠕变特性研究

Experimental Study of Creep Mechanical Properties of Granite at Mengdigou Hydropower Station under Different Loading-Unloading Conditions

针对孟底沟水电站坝区花岗岩开展了不同加卸载应力条件下的三轴蠕变试验,系统分析了不同加卸载过程中坝区花岗岩的变形特征、蠕变速率和破坏强度的变化规律,揭示了蠕变破坏模式。结果表明,孟底沟花岗岩存在蠕变应力门槛值,蠕变后期存在完整的减速、等速和加速蠕变阶段,岩石产生大量塑性变形,体积由压缩转为扩容;轴压恒定相比偏应力恒定卸围压蠕变更具时效特征,卸围压条件下出现劈裂和剪切共存的破坏模式;岩石破坏强度低于常规峰值强度,卸围压相比加轴压方式岩石强度下降幅度更大,粘聚力的降低是造成强度折减的主要因素。

In view of the granite at dam site of Mengdigou hydropower station,the triaxial creep tests under different loading and unloading stress were carried out.The change laws of deformation characteristic,creep rate and fracture strength at different loading and unloading process were analyzed and a failure mode was presented.The results show that the granite at dam site of Mengdigou hydropower station has a threshold value of the creep stress.Three integrated stages exist in the later stage of creep which are decelerated creep stage,constant creep stage and accelerated creep stage.The creep deformations of rocks are very significant and the volume firstly is compressed and then is dilatant.The constant axial compression deformation has more timeliness than that of the deviatoric stress at unloading confining pressure.The destruction mode under the condition of unloading confining pressure is splitting shear joint damage.The strength falling range is wider at unloading confining pressure compared with that of axial compression.The failure strength is lower than the conventional peak strength.The decreased cohesion is the main influencing factors that cause the reduction of strength.