混合型缓冲砌块膨胀性的空间分布及其各向异性

Spatial distribution and anisotropy in swell of compacted bentonite-sand block for HLW buffer barrier

高放废弃物处置过程中,缓冲砌块的膨胀性质是决定缓冲屏障密封效能的主要因素。缓冲砌块的膨胀性与砌块干密度、含水率的空间分布有关;受到砌块制备过程的影响,砌块的膨胀性在不同的方向会表现出一定的各向异性。提出我国高放处置缓冲屏障堆砌建造概念模型,设计了扇形砌块压实模具,并制备大尺寸混合型缓冲砌块。研究选择70%膨润土与30%石英砂混合,以12%目标含水率和1.87g/cm^3目标干密度制备混合型缓冲砌块。压实砌块经切割分解,测试砌块不同空间位置的干密度和含水率分布,并沿着不同方向取标准环刀试样,进行膨胀力与膨胀率试验。结果表明:(1)随着离开压头距离的增大,干密度、含水率分布略有波动。砌块内部不同位置的干密度和含水率分布总体较为均匀。(2)砌块内部不同位置的膨胀力和膨胀率空间分布,与干密度具有良好的对应关系,即干密度越高,对应的膨胀性就越好。(3)砌块膨胀性的各向异性主要体现在竖直方向(制备加压方向)与水平方向之间。定义砌块膨胀力各向异性系数α和膨胀率各向异性系数β,根据试验数据统计分析发现,α=0.856~0.926,β=0.885~0.934。砌块膨胀性各向异性随着干密度的增大而提高。

Swelling of compacted bentonite buffer blocks plays a great role on the sealing of the high-level waste(HLW)depository,which is controlled by dry density and water content distribution in the blocks.Anisotropy in swell properties of bentonite blocks is inevitable because of the differential stress during compaction.This study provides a prototype of fan-shaped bentonite blocks compacted in specially designed mould for constructing HLW buffer barrier in China.The mixture of 70%bentonite and 30%quartz sand was prepared in a target moisture content of 12%,and compacted to a target dry density of 1.87 g/cm^3.The compacted block was primarily cut in small cubes to measure dry density and moisture content,and then cut further into standard rings with specific directions to conduct a series of swelling tests.The results show that:(1)The compacted block has a better uniformity in dry density and moisture content distribution except the position far away from the pressure head.(2)Swell stress and strain distribution is highly corresponded to the dry density distribution,that is,the larger the dry density,the greater the swell.(3)Swell anisotropy is displayed in the vertical,or the compressed direction,rather than the horizontal directions of the block.By defining anisotropy coefficients of swell stressαand anisotropy coefficients of swell strainβ,statistic results indicate thatα=0.856 to 0.926,whileβ=0.885 to 0.934,both of them are elevated with increase dry density.