In situ creep tests on the long-term shear behaviors of a fault located at the dam foundation of Dagangshan hydropower station, China

Faults in the rock mass of dam foundation are crucial in controlling dam deformation and stability. In particular, long-term stability of dam foundation is an important factor for the safety of dam operations. The rock in the foundation of Dagangshan hydropower station is mostly granite, and there are many diabase dikes distributed in granite. Geological survey indicates that many faults exist along the interfaces between granite and diabase. Lots of diabase were metamorphosed to chlorites, which have very low strength. In order to investigate the deformation of faults in diabase dikes under long-term loading, in situ shear creep tests were performed to estimate the creep performance of a fault. The shear creep displacement and the influence of displacement history of the specimen during multi-level loading tests were measured and analyzed. The isochronous stress-strain method was used to determine the long-term strength of the fault in shear creep tests. Considering the instantaneous damage and strain softening, a new viscoelastic-plastic softening creep model was proposed to describe the shear creep behavior of the fault. Comparisons confirmed that this creep model is capable of describing the shear creep behavior of the fault and the creep parameters were estimated accordingly using this model.