Field shear creep test is the most important means to understand the shear creep properties of rock mass. Field shear creep tests are carried out for the dam zone “hard brittle shatter” diabase dikes in Dagangshan hydropower station. The deformation law of shear creep and the characteristics of shear creep rates have been analyzed. The test results show that decay and steady creep only occur when shear stress is relatively low; however

the shear creep rate changes from gradual growth to sudden growth when shear stress reaches the yield strength

the rock breaks in a short time and the acceleration creep appears in the process of shear creep test. Under the constant normal stress

the relation expression between steady-state creep rate and shear stress of diabase can be expressed by an exponential equation. According to the shear creep curves of diabase

the shear creep model of rock is identified. The identification results show that Nishihara model could effectively describe the shear creep properties of dam zone diabase dikes. The shear creep parameters are got through the optimized back analysis method

which provides important mechanical parameters for design and construction of slope in dam zone.