scholarly journals Permeability characteristics and structural evolution of compacted loess under different dry densities and wetting-drying cycles

PLoS ONE ◽  
2021 ◽  
Vol 16 (6) ◽  
pp. e0253508
Author(s):  
Kang-ze Yuan ◽  
Wan-kui Ni ◽  
Xiang-fei Lü ◽  
Xi-jun Wang
Keyword(s):  
Pore Volume ◽  
Permeability Coefficient ◽  
Soil Mechanics ◽  
Structural Evolution ◽  
Aggregate Size ◽  
Total Pore Volume ◽  
Infiltration Rate ◽  
Dry Density ◽  
Permeability Characteristics ◽  
Compacted Loess

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.

scholarly journals Experimental Study on the Saturated Compacted Loess Permeability under K0 Consolidation

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Yan-zhou Hao ◽  
Tie-hang Wang ◽  
Xin Jin ◽  
Lei Cheng ◽  
Jiang-le Li
Keyword(s):  
Permeability Coefficient ◽  
Vertical Direction ◽  
Confining Pressure ◽  
Field Analysis ◽  
Dry Density ◽  
Anisotropy Ratio ◽  
Permeability Test ◽  
Permeability Characteristics ◽  
Permeability Anisotropy ◽  
Compacted Loess

This paper investigates the permeability characteristics of compacted loess by focusing on the anisotropy parallel and perpendicular to the compaction. Three tests are conducted on compacted loess: triaxial permeability test under confining pressure consolidation, triaxial permeability test under K0 consolidation, and SEM test. Samples are maintained and tested at different dry densities under saturated conditions. The test results show that the saturated permeability coefficient of compacted loess is exponentially related to the initial dry density under both confining pressure consolidation and K0 consolidation. The fitting equation can estimate the saturated permeability coefficient of compacted loess at different depths. The horizontal saturated permeability coefficient of compacted loess is larger than that in the vertical direction, showing obvious anisotropy. The saturated permeability anisotropy ratio is linearly related to the initial dry density. Comparing and analysing the saturated permeability coefficient, the saturated permeability coefficient of compacted loess under the K0 consolidation condition is smaller than that under the confining pressure consolidation condition. Under the condition of K0 consolidation, the connectivity of vertical and horizontal pores of compacted loess is weakened, the tortuosity is strengthened, and the void ratio is decreased. K0 consolidation makes the flake-, plate-, and needle-like particles in compacted loess rotate continuously parallel to the compaction surface, which enhances the orientation of particles and leads to the saturated permeability anisotropy increase. The research results provide the basis for water field analysis in loess filling engineering.

scholarly journals Correlations between Air Permeability Coefficients and Pore Structure Indicators of Cementitious Materials

2018 ◽  
Author(s):  
Yuya Sakai
Keyword(s):  
Pore Structure ◽  
Pore Volume ◽  
Percolation Theory ◽  
Permeability Coefficient ◽  
Pore Diameter ◽  
Total Pore Volume ◽  
Cementitious Materials ◽  
Air Permeability ◽  
Permeability Coefficients ◽  
Using Data

Correlations between the air permeability coefficient and various pore structure indicators in cementitious materials were examined to determine the pore structure indicator that best evaluated air permeability using data from previous studies of air permeabilities and pore structures. The determination coefficients of air permeability with total pore volume, critical pore diameter, and ordinary threshold pore diameter were low, although these have often been used as indicators. The median and threshold pore diameters obtained by percolation theory showed high determination coefficients. The equation using the threshold pore diameter better estimated the air permeability coefficient than the Katz–Thompson equation.

Study on the Permeability Characteristics of Coarse-Grained Soil and its Permeability Rule

2014 ◽  
Vol 904 ◽  
pp. 383-388
Author(s):  
Wen Bo Li
Keyword(s):  
Permeability Coefficient ◽  
Void Ratio ◽  
Coarse Grained ◽  
Dry Density ◽  
Fines Content ◽  
Permeability Characteristics ◽  
The Relationship ◽  
Coarse Grained Soil

The permeability of coarse-grained soil is influenced by many factors. The results of permeability tests in different conditions indicate the effects of coarse-grained soil dry density of , fines content P5,void ratio e and nonuniform coefficient Cu to the permeability coefficient. Analyzing the relationship between coarse-grained soil dry density , fines content P5, void ratio e, nonuniform coefficient Cu and permeability coefficient, thus there is a relational expression between coarse-grained soil dry density of soil , fines content P5, void ratio e, nonuniform coefficient Cu and permeability coefficient.

scholarly journals Prediction of Soil-Water Characteristic Curve of Compacted Loess With Different Dry Densities Based on Nuclear Magnetic Resonance

2021 ◽  
Author(s):  
kangze yuan ◽  
Wan kui Ni ◽  
Xiang-Fei LV ◽  
Xiang-ning Li ◽  
Hai-man Wang ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Water Content ◽  
Soil Water ◽  
Pore Volume ◽  
Dry Density ◽  
Residual Water ◽  
Residual Water Content ◽  
Compacted Loess ◽  
Nuclear Magnetic

Abstract Accurate determination of soil-water characteristic (SWCC) is of great importance for understanding the mechanical properties of unsaturated loess. In this study, the compacted loess columns with different dry densities were prepared. Moisture sensor, water potential sensor and nuclear magnetic resonance (NMR) were used to investigate the SWCC and NMR signals intesity of compacted loess under different dry densities. It has been found that with increasing dry density, the saturated water content and the residual water content gradually decreases, but the decrease in residual water content is smaller, and both can establish a linear relationship with dry density. The NMR results showed that the compacted loess pore volume gradually decreased with increasing dry density. When the dry density increased from 1.45 g/cm3 to 1.55 g/cm3, the pore volume of compacted loess decreased by 14.7%, while when the dry density increased from 1.55 g/cm3 to 1.65 g/cm3, the pore volume of compacted loess decreased by 13.2%. The Van Genuchten (VG) model was used to fit the NMR results and SWCC, and a good corresponding relationship was found between the parameters. Therefore, according to the cumulative NMR intensity parameters, SWCC was predicted under different dry densities and the effect was found very well.

Functionalization of Porous Clay Heterostructures with Silane Coupling Agents

2017 ◽  
Vol 54 (2) ◽  
pp. 341-344
Author(s):  
Anda Ionelia Mihai (Voicu) ◽  
Sorina Alexandra Garea ◽  
Eugeniu Vasile ◽  
Cristina Lavinia Nistor ◽  
Horia Iovu
Keyword(s):  
Pore Volume ◽  
Total Pore Volume ◽  
Coupling Agents ◽  
Silane Coupling Agents ◽  
Porous Clay Heterostructures ◽  
Bet Analysis ◽  
Silane Coupling ◽  
Ftir Spectrometry ◽  
Textural Parameters ◽  
Epoxy Groups

The goal of this paper was to study the modification of porous clay heterostructures (PCHs) with various silane coupling agents. Two commercial coupling agents (3-aminopropyl-triethoxysilane (APTES) and 3-glycidoxypropyl-trimethoxysilane (GPTMS)) with different functional groups (amine and epoxy groups) were used as modifying agents for the PCHs functionalization. The functionalization of PCH with APTES and GPTMS was evaluated by Fourier transform infrared (FTIR) spectrometry, thermogravimetric analysis (TGA), X-Ray Diffractions (XRD) and BET Analysis. FTIR spectra of modified PCHs confirmed the presence of characteristic peaks of silane coupling agents. TGA results highlighted an increase of weight loss for the modified PCHs that was assigned to the degradation of silane coupling agents (APTES and GPTMS) attached to the PCHs. The XRD results showed that the structure of modified PCHs was influenced by the type of the silane coupling agent. The functionalization of PCHs with silane coupling agents was also confirmed by BET analysis. Textural parameters (specific surface area (SBET), total pore volume (Vt )) suggested that the modified PCHs exhibit lower values of SBET and a significant decrease of total pore volume than unmodified PCHs.

scholarly journals Nanometer Pore Structure Characterization of Taiyuan Formation Shale in the Lin-Xing Area Based on Nitrogen Adsorption Experiments

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 298
Author(s):  
Chenlong Ding ◽  
Jinxian He ◽  
Hongchen Wu ◽  
Xiaoli Zhang
Keyword(s):  
Specific Surface ◽  
Pore Structure ◽  
Surface Area ◽  
Specific Surface Area ◽  
Shale Gas ◽  
Pore Volume ◽  
Ordos Basin ◽  
Total Pore Volume ◽  
Nitrogen Adsorption ◽  
Taiyuan Formation

Ordos Basin is an important continental shale gas exploration site in China. The micropore structure of the shale reservoir is of great importance for shale gas evaluation. The Taiyuan Formation of the lower Permian is the main exploration interval for this area. To examine the nanometer pore structures in the Taiyuan Formation shale reservoirs in the Lin-Xing area, Northern Shaanxi, the microscopic pore structure characteristics were analyzed via nitrogen adsorption experiments. The pore structure parameters, such as specific surface area, pore volume, and aperture distribution, of shale were calculated; the significance of the pore structure for shale gas storage was analyzed; and the main controlling factors of pore development were assessed. The results indicated the surface area and hole volume of the shale sample to be 0.141–2.188 m2/g and 0.001398–0.008718 cm3/g, respectively. According to the IUPAC (International Union of Pure and Applied Chemistry) classification, mesopores and macropores were dominant in the pore structure, with the presence of a certain number of micropores. The adsorption curves were similar to the standard IV (a)-type isotherm line, and the hysteresis loop type was mainly similar to H3 and H4 types, indicating that most pores are dominated by open type pores, such as parallel plate-shaped pores and wedge-shaped slit pores. The micropores and mesopores provide the vast majority of the specific surface area, functioning as the main area for the adsorption of gas in the shale. The mesopores and macropores provide the vast majority of the pore volume, functioning as the main storage areas for the gas in the shale. Total organic carbon had no notable linear correlation with the total pore volume and the specific surface area. Vitrinite reflectance (Ro) had no notable correlation with the specific surface area, but did have a low “U” curve correlation with the total pore volume. There was no relationship between the quartz content and specific surface area and total pore volume. In addition, there was no notable correlation between the clay mineral content and total specific surface area and total pore volume.

scholarly journals Microporous Materials Based on Norbornadiene-Based Cross-Linked Polymers

Polymers ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1382 ◽  
Author(s):  
Dmitry Alentiev ◽  
Dariya Dzhaparidze ◽  
Natalia Gavrilova ◽  
Victor Shantarovich ◽  
Elena Kiseleva ◽  
...  
Keyword(s):  
Pore Volume ◽  
Total Pore Volume ◽  
Amorphous Polymers ◽  
Co2 Uptake ◽  
Wide Angle ◽  
X Ray Diffraction ◽  
Pd Catalysts ◽  
X Ray ◽  
Positron Annihilation Lifetime ◽  
Surface Areas

New microporous homopolymers were readily prepared from norbornadiene-2,5, its dimer and trimer by addition (vinyl) polymerization of the corresponding monomers with 60–98% yields. As a catalyst Pd-N-heterocyclic carbene complex or Ni(II) 2-ethylhexanoate activated with Na+[B(3,5-(CF3)2C6H3)4]− or methylaluminoxane was used. The synthesized polynorbornenes are cross-linked and insoluble. They are glassy and amorphous polymers. Depending on the nature of the catalyst applied, BET surface areas were in the range of 420–970 m2/g. The polymers with the highest surface area were obtained in the presence of Pd-catalysts from the trimer of norbornadiene-2,5. The total pore volume of the polymers varies from 0.39 to 0.79 cm3/g, while the true volume of micropores was 0.14–0.16 cm3/g according to t-plot. These polymers gave CO2 uptake from 1.2 to 1.9 mmol/g at 273 K and 1 atm. The porous structure of new polymers was also studied by means of wide-angle X-ray diffraction and positron annihilation lifetime spectroscopy.

scholarly journals Effect of Structure and Chemical Activation on the Adsorption Properties of Green Clay Minerals for the Removal of Cationic Dye

2018 ◽  
Vol 8 (11) ◽  
pp. 2302 ◽  
Author(s):  
Abdelfattah Amari ◽  
Hatem Gannouni ◽  
Mohammad Khan ◽  
Mohammed Almesfer ◽  
Abubakr Elkhaleefa ◽  
...  
Keyword(s):  
Clay Minerals ◽  
Pore Volume ◽  
Acid Treatment ◽  
Structural Changes ◽  
Chemical Activation ◽  
Total Pore Volume ◽  
Batch Adsorption ◽  
Acid Activation ◽  
Cationic Dye ◽  
Average Pore

In this study, natural clay minerals with green appearance were treated with sulfuric acid. Mass percentage of acid (wt%), temperature (T), contact time (t) and liquid-to-solid mass ratio (R) are used as the prevailing factors that determine the extent of acid-activation. The values of these factors range from 15–50%, 60–90 °C, 1.5–6 h and 4–7, respectively. The study has focused on the structural changes as well as textural characteristics of the clay. Three activated clay samples were prepared under different treatment conditions. The samples were characterized using X-ray powder diffraction (XRD), fourier transform infrared (FTIR), scanning electron microscope (SEM), chemical analysis and N2 adsorption techniques. Characterization of the treated clay minerals exhibited significant structural changes to a greater extent of acid-activation, from being partially crystalline to being amorphous silica. The surface area and total pore volume of clay increased proportionally with the level of acid treatment. The average pore diameter behaved differently. During the strong acid treatment, a large increase in pore volume and the enlargement of the pore size distribution were observed. This suggests that considerable structural changes and partial destruction may have occurred in this condition. The removal of methylene blue, used as cationic dye, from aqueous solution by the batch adsorption technique on three prepared acid-activated clay samples was studied. The Langmuir model was found to agree well with the experimental data.

Test Investigation on Mechanical of Unsaturated Loess

2012 ◽  
Vol 204-208 ◽  
pp. 22-27
Author(s):  
Yan Zhu ◽  
Yun Xu Chen
Keyword(s):  
Water Content ◽  
Horizontal Plane ◽  
Mechanical Characteristics ◽  
Loess Soil ◽  
Dry Density ◽  
One Dimensional ◽  
Test Investigation ◽  
Unsaturated Loess ◽  
Test Result ◽  
Compacted Loess

Compression and collapse of unsaturated compacted loess are studied by using dry density and water content which easily controlled in engineering, the controlling range of dry density and water content are confirmed respectively. Then the deformation of compression and collapse and the frequency of engineering damager occurrence can be decreased. In addition, the mechanical characteristics of loess in different directions may differ because the loess was consolidated only under the condition of its upper weight of soil and load. The conventional mechanical experiments, including one-dimensional compress and collapse test, were conducted with the specimen of loess soil in different angle from the original horizontal plane. The test result shows that the loess is anisotropic

scholarly journals An Eco-Friendly Process for Removal of Lead from Aqueous Solution

2017 ◽  
Vol 11 (5) ◽  
pp. 47 ◽  
Author(s):  
Heman A. Smail ◽  
Kafia M. Shareef ◽  
Zainab H. Ramli
Keyword(s):  
Heavy Metal ◽  
Oxalic Acid ◽  
Surface Area ◽  
Pore Volume ◽  
Metal Ion ◽  
Adsorption Equilibrium ◽  
Total Pore Volume ◽  
Heavy Metal Ion ◽  
Bet Surface Area ◽  
Barley Husk

The adsorption of lead (Pb II) ion on different types of synthesized zeolite was investigated. The BET surface area, total pore volume & average pore size distribution of these synthesized zeolites were determined by adsorption isotherms for N2, the surface area & total pore volume of their sources were found by adsorption isothermN2.The adsorption equilibrium was measured after 24h at room temperature (RT) & concentration 10mg.L-1 of Pb (II) was used. The adsorption of heavy metal Pb (II) on four different prepared zeolites (LTA from Montmorillonite clay, FAU(Y)-B.H (G2) from Barley husk, Mordenite (G1) from Chert rock, FAU(X)-S.C (G3) from shale clay & modified Shale clay by oxalic acid (N1) & sodium hydroxide (N2)), were compared with the adsorption of their sources by using static batch experimental method. The major factors affecting the heavy metal ion sorption on different synthesized zeolites & their sources were investigated. The adsorption equilibrium capacity (Qm) of Pb (II) ion for different synthesized zeolites ordered from (N1>N2>LTA>G3>G2>G1&for their sources ordered Shale clay >Montmorilonite> Barley husk>Chert rock. The atomic absorption spectrometry was used for analysis of lead heavy metal ion, the obtained results in this study showed that the different synthesized zeolites were efficient ion exchanges for removing heavy metal, in particular, the modified zeolite from shale clay by oxalic acid.

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