高放废物地质处置库中缓冲回填材料的收缩特征

Shrinkage characteristics of buffer-backfilling materials in high-level radioactive waste geological disposal

缓冲回填材料的收缩特征对高放废物处置库的安全性和稳定性有重要影响。以COx泥岩缓冲回填材料为研究对象,采用不同的试验方法分别研究了饱和的压实试样和糊状试样在干燥过程中的体积收缩变形特征。试验结果表明:压实试样的体积收缩变形特征受初始干密度的影响比较明显,缩限、收缩系数和收缩应变均随初始干密度的增加而减小;压实试样的体积收缩存在明显的各向异性,在低压实度条件下,径向收缩大于轴向收缩,收缩几何因子大于3,在高密度条件下,轴向收缩大于径向收缩,收缩几何因子小于3;糊状试样的体积收缩过程可分为正常收缩、残余收缩和零收缩3个阶段,且绝大部分体积收缩变形发生在试样变为非饱和之前;相对于其他收缩模型,G&C模型对COx糊状试样收缩曲线的拟合精度最高。

The shrinkage characteristics of buffer-backfilling materials play an important role in the security and stability of the high-level radioactive waste geological disposal system. COx argillite is considered as a kind of potential buffer-backfilling materials in France. In this investigation, both the initially saturated compacted COx specimens and the paste-like COx specimens are prepared and subjected to different test methods to study their volumetric shrinkage behaviours. For the compacted specimens, it is found that the volumetric shrinkage deformation is significantly influenced by the initial dry density; the shrinkage limit, shrinkage efficiency and shrinkage strain decrease with the increasing dry density; in addition, it is observed that the shrinkage direction of specimens shows obvious anisotropism. For example, at low degree of compaction, the radial shrinkage strain is higher than axial shrinkage strain, and the shrinkage geometry factor is larger than 3; however, the contrary results are obtained at high degree of compaction. For the paste-like specimens, three shrinkage stages can be distinguished： normal shrinkage, residual shrinkage and zero shrinkage; most of the volume shrinkage deformation occurs before the air-entry point while the soil is still fully saturated. A group of four general shrinkage models are employed to fit the shrinkage curve of the paste-like specimens. The results show that the G ＆ C model can get the highest performance for the present soil.