向家坝水电站含弱面砂岩剪切蠕变试验研究

INVESTIGATION ON SHEAR CREEP EXPERIMENTS OF SANDSTONE WITH WEAK PLANE IN XIANGJIABA HYDROPOWER STATION

向家坝水电站左岸坝基开挖过程中揭露出挤压带,该挤压带砂岩岩体质量差,其显著的蠕变变形对水工建筑物的安全稳定性不利。利用CSS–3940YJ型岩石剪切流变试验机,对挤压带含弱面砂岩进行剪切蠕变试验。试验结果表明:该岩石蠕变量大,破坏前剪应变为1.73%～8.05%,具有显著的延性特征,属于典型的软岩。正应力提高了岩石的延性特性。在恒定正应力下,岩石蠕变速率随剪应力水平的增大而增大。基于采集的大量试验数据,采用差分法求得每一时刻的蠕变速率,并利用幂函数对蠕变速率曲线进行拟合,分析表明蠕变稳定所需时间随剪应力水平的增大而增大。通过对破坏断口的分析发现:岩石内部微裂隙随剪应力水平和时间的增长而不断扩展直至贯通,致使岩石发生剪切破坏。该研究成果对向家坝水电站坝基工程有重要参考价值。

The compressive zone was revealed in the excavation of left bank dam foundation of Xiangjiaba Hydropower Station. The quality of sandstone in the zone is poor,and its significant creep deformation is harmful to hydraulic structures. Shear creep experiments were carried out for the sandstone with weak plane by using CSS– 3940YJ rock shear rheology testing machine. The results show that large creep deformation of the sandstone occurs in the experiment. Before the damage,the shear strain reaches 1.73%–8.05%. The rock is of significant ductility characteristics,and it is typical soft rock. The normal stress enhances the ductility of rock. At a constant normal stress,the creep rate of the rock increases with the increase in shear stress level. Based on large amounts of experimental data,the creep rates at every moment are calculated by difference methods,and the power function is used to fit the rate curve. The analysis shows that the time required for creep stability of rock increases with increase in shear stress level. It is found through the analysis of the fracture that the internal microcracks of rock expand with the increase in shear stress level and time until coalescence resulting in shear failure of the rock. The achievements offer important referential value for the research on dam foundation of Xiangjiaba Hydropower Station.