中文摘要：

甘肃北山是我国高放废物深地质处置的预选场址,其花岗岩具有完整性及均匀性好、孔隙率及渗透率低等重要特点。采用气体瞬态压力脉冲法测试不同围压下北山花岗岩在三轴压缩过程中的渗透率变化特征。结合花岗岩在偏应力演化过程中微裂纹的萌生、扩展机制以及应力–应变曲线的变化特征分析,采用细观力学方法研究北山花岗岩在三轴压缩过程中渗透率的演化机制。分析结果表明：（1）北山花岗岩的初始渗透率在10-19 m2量级,对应于应力–应变曲线,其渗透率曲线随着偏应力增加总体呈现出下降段、水平段、稳定增长段以及急剧上升段的变化特征;（2）初始微裂纹的压缩闭合可导致试样的渗透率下降约1个数量级,峰前破坏时渗透率的增幅可达2-3个数量级,围压从5 MPa增大至10 MPa可导致渗透率减小1个数量级;（3）细观力学模型的计算值与试验值吻合良好,北山花岗岩试样的宏观力学响应及渗透特性与试样内部微裂纹的细观结构特征及连通性的变化密切相关,岩石渗透率变化和损伤演化具有良好的一致性,且损伤的发育可导致渗透率呈现较弱的各向异性特征。研究成果对于我国高放废物深地质处置工程中围岩的开挖扰动机制、渗透特性演化规律以及处置库系统的性能评价具有重要意义。

英文摘要：

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.