混合型缓冲材料砌块渗透性及其各向异性研究

缓冲材料砌块具备良好的防渗性能，是保证高放废物处置库封闭性的关键。缓冲材料砌块经单轴加载挤压成型，块体尺寸大，测试与评价其渗透性能的均匀性和各向异性，对缓冲屏障设计具有重要价值。研究制备不同干密度的混合型缓冲材料砌块，定向切割获得砌块内部不同位置、不同方向的小试样，开展刚性壁和柔性壁渗透试验，综合评价了混合型缓冲砌块不同方向的水力传导系数。研究结果表明：砌块干密度越大，砌块的水力传导系数越低。所有砌块的水力传导系数均处于10?10 cm/s数量级，沿砌块z、?、r方向的水力传导系数基本相等，表明砌块渗透性具有良好的均匀性和各向同性，且满足高放缓冲材料防渗要求。两种试验方法获得的渗透结果差异较小，柔性壁渗透条件下砌块产生10%～20%的体积膨胀，导致其水力传导系数略大于刚性壁下的平行试样。引入CT试验，分析了渗透前后砌块的微观特性变化。试验证实，在饱和渗透之后，以CT值显示的砌块密度分布趋于均匀，砌块内部存在的微裂隙愈合消失。

Hydraulic conductivity and anisotropy of hybrid buffer material blocks

The impermeability of compacted buffer block is a key parameter to ensure the sealing of high-level radioactive waste (HLW) repository. It is importance of testing and evaluating the uniformity and anisotropy of the permeability of the buffer material blocks to the design of buffer barrier because the blocks are compressed under uniaxial loading with a large size. In this work, full-sized blocks of bentonite-sand mixture were compacted into different dry densities, cut with electric saw to get smaller pieces at various positions and directions, and tested by both rigid-wall and flexible wall permeameter to evaluate the overall hydraulic conductivity of the blocks. Test results show that the hydraulic conductivity decreases with the increase in block density, and all blocks fall into the order of 10?10 cm/s along the directions of z, ? and r of the blocks. This proves that the compacted blocks possess satisfactory homogeneity and marginal anisotropy in permeability, and meet the low requirements of the buffer barrier for HLW repository. With respect to both permeameters, specimens in flexible wall permeameter expanded 10%?20% than those in rigid-wall permeameter, leading to a slight increase in the hydraulic conductivity than the rigid one. Before and after permeation, CT test was introduced to investigate the microstructure evolution of the blocks. After permeation, the density distribution of the specimen as indicated by CT value transformed uniformly than before, and the micro crack was healed to become unobservable.