Department of Geological Engineering, College of Geological Engineering and Surveying and Mapping, Chang'An University, Xi'an, Shaanxi, China.
School of Water and Environment, Chang'An University, Xi'an, Shaanxi, China.
PLoS One. 2021 Jun 28;16(6):e0253508. doi: 10.1371/journal.pone.0253508. eCollection 2021.
Permeability characteristics of compacted loess is always an important topic in soil mechanics and geotechnical engineering. This study explored the permeability characteristics of compacted loess under different dry densities and wetting-drying cycles, and found that as the dry density increases, the compacted loess surface became denser, the saturation permeability coefficient and saturation infiltration rate decreased. However, the wetting-drying cycle presented the opposite result. Meanwhile, the evolution of the microstructure was investigated by Scanning Electron Microscope (SEM) and Nuclear Magnetic Resonance (NMR) to explain the change of its permeability characteristics. The size of compacted loess aggregates was quantitatively analyzed by Image-Pro Plus (IPP) software. It showed that the size of compacted loess aggregates for different dry densities were concentrated from 10-100 μm, occupying 65.0%, 58.19%, and 51.64% of the total aggregates area respectively. And the interesting finding was that the area occupied by 10-50 μm aggregates remained basically unchanged with the number of wetting-drying cycles increasing. Therefore, the size of 10-50 μm aggregates represented the transition zone of compacted loess. NMR analyses revealed that with increasing dry density, the volume of macropores in the compacted loess rapidly decreased, the volume of mesopores and small pores increased. Meanwhile, the change in micropores was relatively small. The pore volume of the compacted loess after three wetting-drying cycles increased by 8.56%, 8.61%, and 6.15%, respectively. The proportion of macropores in the total pore volume shows the most drastic change. Variations in aggregate size and connection relationships made it easier to form overhead structures between aggregates, and the increased of macropore volume will form more water channels. Therefore, the change in permeability characteristics of compacted loess is determined by aggregate size, loess surface morphology, and the total pore volume occupied by macropores.
压实黄土的渗透性特征一直是土壤力学和岩土工程中的一个重要课题。本研究探讨了不同干密度和干湿循环下压实黄土的渗透性特征，发现随着干密度的增加，压实黄土表面变得更加密实，饱和渗透系数和饱和入渗率降低。然而，干湿循环则呈现出相反的结果。同时，通过扫描电子显微镜（SEM）和核磁共振（NMR）研究了微观结构的演化，以解释其渗透性特征的变化。通过 Image-Pro Plus（IPP）软件定量分析了压实黄土团聚体的大小。结果表明，不同干密度下压实黄土团聚体的大小集中在 10-100μm 之间，分别占总团聚体面积的 65.0%、58.19%和 51.64%。有趣的是，随着干湿循环次数的增加，10-50μm 团聚体所占据的面积基本保持不变。因此，10-50μm 团聚体的大小代表了压实黄土的过渡区。NMR 分析表明，随着干密度的增加，压实黄土中大孔体积迅速减少，中孔和小孔体积增加。同时，微孔的变化相对较小。经过三次干湿循环后，压实黄土的孔隙体积分别增加了 8.56%、8.61%和 6.15%。总孔体积中大孔的比例变化最大。团聚体大小和连接关系的变化使得团聚体之间更容易形成架空结构，大孔体积的增加将形成更多的水流通道。因此，压实黄土渗透性特征的变化取决于团聚体大小、黄土表面形态以及大孔体积在总孔隙体积中所占的比例。
