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Abstract Due to the good integrity，homogeneity and low porosity and permeability of Beishan granite，Beishan has been considered as a candidate for high-level radioactive waste repository. In this study，triaxial compression tests with the measurements of permeability were performed on granite samples using the gas pulse transient technique. Based on the observations of the initiation and propagation of microcracks in the granite samples and the characteristics of the strain-deviatoric stress curves，the permeability variation of the granite samples with the deviatoric stress was analyzed with a micromechanical model. The initial permeability of the Beishan granite at zero deviatoric stress state is in the magnitude of 10－19 m2. The permeability decreases in the initial region of microcrack closure，keeps constant in the elastic region，increase stably and then dramatically the following the unstable regions of crack growth. The closure of preexisting microcracks in the initial loading stage leads to a reduction of permeability of one order in magnitude. The permeability at the failure state increases 2–3 orders of magnitude. The increase of confining pressure from 5 MPa to 10 MPa induces a permeability decrease of one order in magnitude. The numerical simulated results with the micromechanical model are in good agreements with the experimental data，which verifies that the mechanical and hydraulic properties of the granite on the macroscopic scale are essentially governed by the alterations of the microstructural features and the crack connectivity. The permeability variation of the granite samples is consistent with the growth of damage density，in which weak anisotropy of the permeability is the result of the damage growth pattern. The results achieved in this study are useful for assessment of the excavation-induced damage zone，the permeability variation and the long-term performance of the high-level radioactive waste repository systems.
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Received: 06 July 2014
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2014, Vol. 33 
