金沙江向家坝水电站坝基砂岩蠕变特性研究

Research on Creep Characteristics of Sandstone on Dam Foundation of Xiangjiaba Hydropower Station in Jinshajiang River

选取了金沙江向家坝水电站坝基的典型砂岩试样,采用三轴压缩试验对砂岩蠕变特性进行研究,分析了流变失稳破坏时的特征及砂岩的轴向、侧向和体积应变的全过程蠕变曲线异同点,对砂岩的长期强度进行预测分析。试验结果表明,砂岩存在一个起始蠕变应力阈值,每级荷载下的蠕变曲线之前都存在一个瞬时应变且随着围压的增大和偏应力的增大幅度越来越小,轴向瞬时应变与偏应力具有很好的线性关系;侧向和体积变形则存在明显的蠕变三阶段,加速阶段要比轴向快且两者的蠕变曲线形状相似,在同一围压和同一级偏应力下侧向蠕变量比轴向及体积的大,其蠕变发展最快;砂岩的长期强度可用等时偏应力应变曲线簇来进行确定,采用体积偏应力应变曲线簇更适宜,在已有的流变模型中伯格斯模型能较好的反映砂岩蠕变特性。

The typical sandstone on dam foundation of Xiangjiaba hydropower station are taken samples. The creep characteristics of the sandstone are studied by triaxial compression tests. The damage characteristics of instability phase, axial strain, lateral strain and volume strain of the whole process of creep curve are analyzed, then the long-term strength of sandstone is evaluated. The results show that there is a starting stress threshold of sandstone under creepage, each creep curve has a instantaneous strain under each load which the instantaneous strain will decrease with the increase of confining stress and deviatoric stress, the axial instantaneous strain has well linear relation with the deviatoric stress. There are obvious three phases for lateral strain and volume strain, and the lateral strain and volume strain have higher growth rate than the axial strain while the creep curves are similar to each other. The lateral creep strain is higher than the axial and volume creep strain under the same confining stress or deviatoric stress. The long-term strength of sand- stone can be determined by the partial stress-strain curve clusters which the volume partial stress-strain curve cluster is the best. Final- ly, the burgers model is most suitable model to simulate the creep characteristic of sandstone amond the current rheological constitu- tive models .