On the Relationship between Creep Strain and Permeability of Granite: Experiment and Model Investigation

Granite is regarded as a good option of host rock for high-level radioactive waste (HLW) repositories. Despite of its creep strain is small, the creep damage of which, especially that in the accelerated creep stage, increase its permeability significantly. To investigate the relationship between the creep strain and permeability evolution in granite, the present paper conducted a set of creep-seepage experiments associated with acoustic emission (AE) technology. The analysis in terms of the evolution of creep strain and permeability, characters of AE hits, mechanism of creep strain and that of permeability convince us that, the permeability evolution of granite is related to the volumetric dilation and microcracks connectivity. According to this relationship, a three-dimensional damage-based creep model was deduced from a one-dimensional fractal derivative-based model, and a permeability evolution model was proposed as well in this paper. The experiment data suggest nonnegligible influence of creep damage on the permeability of granite, therefore this influence should be taken into consideration of the design work of HLW repositories. The calculated results of the proposed models match well the experiment data, suggesting good capability of the models in approaching the creep and hydraulic performance of granite. In addition, the permeability model is friendly in parameter identification due to its simple mathematic formulation.