Voids effect on the swelling behaviour of compacted bentonite
Voids effect on the swelling behaviour of compacted bentonite
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DOI：
10.1680/jgeot.17.p.283
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发表时间：
2019-07-01
期刊：
影响因子：
5.8
通讯作者：
Li, Xiao-Zhao
中科院分区：
文献类型：
--
作者：
Bian, Xia;Cui, Yu-Jun;Li, Xiao-Zhao
本文研究了压实MX 80膨润土在水化条件下的膨胀行为，初始孔隙的存在模拟了真实的核废料处置库中的工艺孔隙。当水从初始孔隙引入试样时，膨润土首先填充初始孔隙，然后产生膨胀压力。在不同的水化时间，微观结构进行了研究，在不同的高度（初始空隙，顶部，中部和底部），使用压汞孔隙率法，连同干密度，含水量和吸力的测定。据观察，微观结构的特点是存在一个大的和一个小的孔家庭在底部和中间层，但通过创建一个新的中孔家庭的主导孔模式约0.04-2 μ m的顶部和初始空隙层后，空隙空间填充膨胀膨润土。从底部到孔隙，中孔隙的显著增加伴随着不可及孔隙的增加和大孔隙和小孔隙的减少。进一步的研究表明，根据孔隙比随膨胀压力的变化，可以将样品分为压缩区和膨胀区：在压缩区，土壤随时间推移而压缩，其特征是中孔和大孔显著减少;而在膨胀区，土壤仍在发生膨胀，其代表是不可接近的孔和中孔增加。此外，微观结构的变化沿着样品被发现是很好的相关性的变化，干密度和水含量：水含量减少，干密度增加，从初始的空隙到底部的位置;随着时间的推移，上部的干密度增加，由于压缩，而下部的干密度降低，由于溶胀。这为压实膨润土膨胀的主要机制提供了证据：膨胀的膨润土首先填充初始空隙，然后通过后面的膨润土膨胀进行压缩。
This paper investigates the swelling behaviour of compacted MX80 bentonite under hydration with the presence of initial voids that simulate the technological voids in real nuclear waste repositories. With water introduced into samples from the initial voids, the swollen bentonite first filled up the initial voids, and then swelling pressure was generated. At different hydration times, the microstructure was investigated at different heights (initial void, top, middle and bottom) using mercury intrusion porosimetry, together with the determination of dry density, water content and suction. It was observed that the microstructure was characterised by the presence of a large-and a small-pore families at bottom and middle layers, but by the creation of a new medium-pore family with dominant pore mode around 0.04-2 mu m at the top and initial void layers after the void space was filled by swollen bentonite. From bottom to void, the significant increase in medium pores was accompanied by an increase in inaccessible pores and a decrease in large and small pores. Further examination showed that the sample could be divided into compression and swelling zones based on the variation of void ratio with swelling pressure: at the compression zone, the soil was compressed over time, characterised by a significant reduction of medium and large pores; whereas at the swelling zone, the soil was still undergoing swelling, represented by the increase of inaccessible pores and medium pores. In addition, the changes in microstructure along the sample were found to be well correlated with changes in dry density and water content: the water content was decreasing and the dry density was increasing from the initial void to the bottom positions; over time the dry density of the upper part was increasing due to compression, while the dry density of the lower part was decreasing due to swelling. This provided evidence for the main mechanism of compacted bentonite swelling with the presence of technological voids: the swollen bentonite fills the initial voids first and then undergoes compression by the swelling of the bentonite behind.