Dataset Information

Three-dimensional pore characterization of intact loess and compacted loess with micron scale computed tomography and mercury intrusion porosimetry.

ABSTRACT: The pore structure is one of the most important properties of soil, which can directly affect the other properties such as water content, permeability and strength. It is of great significance to study the soil pore structure for agricultural cultivation, water and soil conservation and engineering construction. This paper investigates the 3D pore characterization of intact loess and four kinds of compacted loess (with different dry density) in northwest China. Micro scale computed tomography and mercury intrusion porosimetry tests were performed to get the porosity, specific surface area, pore size distribution, connected pores content and isolated pores content of different samples. Results show that the intact loess has more connected pores than the compacted loess, and the compacted loess whose dry density appears to be modelled well still have different pore structure with the intact loess. In addition, as the compactness increasing, the large pores (>13 ?m) were firstly broken into medium pores (8~13 ?m) and some small pores (<8 ?m) until the pore structure was close to the natural structure of the intact loess, after that medium pores began to be broken into small pores.

SUBMITTER: Zhang L

PROVIDER: S-EPMC7244767 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature

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Three-dimensional pore characterization of intact loess and compacted loess with micron scale computed tomography and mercury intrusion porosimetry.

Zhang Linxin L Qi Shengwen S Ma Lina L Guo Songfeng S Li Zhiqing Z Li Guoliang G Yang Jijin J Zou Yu Y Li Tonglu T Hou Xiaokun X

Scientific reports 20200522 1

The pore structure is one of the most important properties of soil, which can directly affect the other properties such as water content, permeability and strength. It is of great significance to study the soil pore structure for agricultural cultivation, water and soil conservation and engineering construction. This paper investigates the 3D pore characterization of intact loess and four kinds of compacted loess (with different dry density) in northwest China. Micro scale computed tomography an ...[more]

PMID: 32444623

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Project description: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.

Project description:Hydromechanical and structural properties of compacted loess have a significant impact on the stability and reliability of subbase and subgrade, which needs to be quickly determined in the field and laboratory. Hence, an electrical resistivity method was used to characterize the hydromechanical and structural properties of compacted loess during constant rate of strain compression. In the present work, compacted loess samples with a dry density of 1.7 g/cm3, a diameter of 64 mm, a height of 10 mm and different water content ranging from 5-25% were prepared. The constant rate of strain (CRS) tests were conducted by a developed oedometer cell equipped with a pair of horizontal circular electrodes (diameter of 20 mm) and vertical rectangular electrodes (width of 3.5 mm) to determine the electrical resistivity of compacted loess. The results showed that as average water content increases, plastic compression indices increase from 0.220 to 0.350 and the elastic compression indices increase from 0.0152 to 0.030, but they decrease to 0.167 and 0.010 and yield stress decreases from 381.28 kPa to 72.35 kPa. Moreover, as vertical strain increases, the variation trend of average formation factor and average shape factor for the lower water content decreases but increases for the maximum water content, and the anisotropy index first decrease and then tend to increase slightly, which indicates that the structural properties of unsaturated and saturated samples during compression exhibits different trend and the anisotropy of samples tend to be stable as vertical strain increases. As the water content increases, the average formation factor and average shape factor decrease, but the anisotropy index first decreases then increases, suggesting that water content has a significant impact on these electrical indices. More important, The coefficients of average formation factor decrease from 33.830 to -1.698 and the coefficients of average shape factor decrease from 8.339 to -0.398 as water content increases, whereas there is less variation for the coefficient of anisotropic index with a value of 2.190. An equation correlating average formation factor and water content and vertical strain is regressed to characterize the hydromechanical properties of compacted loess by measuring its impedance, which can be used to evaluate the stability of compacted loessic ground and subgrade.

Dataset Information

Three-dimensional pore characterization of intact loess and compacted loess with micron scale computed tomography and mercury intrusion porosimetry.

Publications

Three-dimensional pore characterization of intact loess and compacted loess with micron scale computed tomography and mercury intrusion porosimetry.

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