Influences of degree of saturation and stress cycle on gas permeability of unsaturated compacted Gaomiaozi bentonite

2019 ◽  
Vol 254 ◽  
pp. 54-62 ◽  
Author(s):  
Tianyu Wei ◽  
Dawei Hu ◽  
Hui Zhou ◽  
Jingjing Lu ◽  
Tao Lü
Keyword(s):  
Gas Permeability ◽  
Degree Of Saturation ◽  
Stress Cycle ◽  
Gaomiaozi Bentonite

Influence of clod size and water content on gas permeability of a compacted loess

2014 ◽  
Vol 51 (12) ◽  
pp. 1468-1474 ◽  
Author(s):  
T.L.T. Zhan ◽  
Y.B. Yang ◽  
R. Chen ◽  
C.W.W. Ng ◽  
Y.M. Chen
Keyword(s):  
Water Content ◽  
Power Function ◽  
Soil Structure ◽  
Gas Permeability ◽  
High Water ◽  
Degree Of Saturation ◽  
Northwestern Region ◽  
Water Contents ◽  
Compacted Loess ◽  
Compaction Degree

The northwestern region of China is mainly semi-arid to arid and loess is ubiquitous. This natural resource has considerable potential to be transformed into earthen final covers for local landfills, but first its suitability must be ascertained through extensive tests. In this study, a device was developed to measure the gas permeability of unsaturated compacted loess specimens. Experiments were carried out to investigate the influence of clod size, compaction water content, and post-compaction water content on the gas permeability of the compacted loess. To maintain an identical soil structure, the post-compaction water content was changed using the osmotic technique. It was found that the compaction water content and resultant soil clod size exerted a combined effect on the gas permeability such that, at low water contents, the gas permeability remained fairly constant, but at high water contents the clods became relatively large, and the effect of the clod size dominated the water blockage effect from increasing water content. For specimens with identical soil structure, the gas permeability decreased with the increasing post-compaction degree of saturation at an accelerated rate. A power function is proposed to predict the relationship between the gas permeability normalized by the porosity function of the Kozeny–Carmen model and the post-compaction degree of saturation. Analysis of the experimental data indicates that the parameters for the power function still depend on the porosity of the compacted loess, particularly at high degrees of saturation.

Undrained Behavior of Unsaturated Bentonite-Sand Mixture

2012 ◽  
Vol 446-449 ◽  
pp. 1454-1457
Author(s):  
Wen Jing Sun ◽  
De An Sun ◽  
Jin Yi Zhang
Keyword(s):  
Confining Pressure ◽  
Degree Of Saturation ◽  
Dry Density ◽  
Compression Tests ◽  
Shear Tests ◽  
Isotropic Compression ◽  
Sand Mixture ◽  
Mechanical Behaviours ◽  
Undrained Behavior ◽  
Gaomiaozi Bentonite

The strength, deformation and hydro-mechanical behaviours of a compacted unsaturated Gaomiaozi bentonite-sand mixture under undrained condition are studied by conducting a series of isotropic compression tests and triaxial shear tests under constant water content. During undrained isotropic compression testing, void ratio and suction decrease while degree of saturation increases. The stress-strain relations are obtained from undrained triaxial shear tests. The volume contraction and lateral expansion can be observed. The suction decreases with increasing shearing. The net confining pressure and initial dry density affect the initial rigidity, undrained shear strength, volumetric deformation and hydro-mechanical behaviour.

scholarly journals Impact of dry density, saturation, and confinement on gas permeability of clay-barrier materials

2020 ◽  
Vol 205 ◽  
pp. 10006
Author(s):  
Bohan Zhou ◽  
Marcelo Sanchez ◽  
María Victoria Villar
Keyword(s):  
Gas Flow ◽  
Fuel Cycle ◽  
Gas Permeability ◽  
Degree Of Saturation ◽  
Dry Density ◽  
Flow Process ◽  
Human Environment ◽  
Barrier Materials ◽  
High Level ◽  
Clay Barrier

The safe isolation of high-level radioactive waste from the human environment is a key requisite in the nuclear fuel cycle. Deep geological repositories (i.e. >500m) in a suitable rock mass, involving both engineered and natural barriers is currently the most favoured option for the disposal of high-level nuclear waste. Complex Thermal-Hydro-Mechanical and Chemical (THMC) phenomena are anticipated during the repository lifetime. The formation of gasses (e.g., as a result of oxidation processes) and their possible migration through the engineered barrier system (EBS) could jeopardise the main barrier functions. This paper focuses on the experimental study of the gas flow process through clay-barrier materials, particularly on the effect of degree of saturation, clay initial dry density, and confinement stress on gas permeability. It is shown that the initial dry density of the clay has a significant impact on gas flow, especially at low saturations. As expected, lower gas permeability values were obtained near saturation. Confinement has a minor impact on gas flow, at least for the range of stresses investigated in this paper.

Gas permeability of concrete in relation to its degree of saturation

1999 ◽  
Vol 32 (1) ◽  
pp. 3-8 ◽  
Author(s):  
A. Abbas ◽  
M. Carcasses ◽  
J. -P. Ollivier
Keyword(s):  
Gas Permeability ◽  
Degree Of Saturation

Gas permeability of a compacted bentonite–sand mixture: coupled effects of water content, dry density, and confining pressure

2015 ◽  
Vol 52 (8) ◽  
pp. 1159-1167 ◽  
Author(s):  
Jiang-Feng Liu ◽  
Frédéric Skoczylas ◽  
Jean Talandier
Keyword(s):  
Water Content ◽  
Gas Permeability ◽  
Confining Pressure ◽  
Degree Of Saturation ◽  
Dry Density ◽  
Sand Mixture ◽  
Compacted Bentonite ◽  
High Confining Pressure ◽  
Confining Pressures ◽  
Gas Tightness

The gas-tightness of compacted bentonite–sand mixtures is important to the total sealing efficiency of geological repositories. The initial aim of this work was to determine whether the combination of a high confining pressure (Pc) and incomplete saturation could cause a bentonite–sand mixture to become gas-tight. The results show that the physical characteristics of the materials (degree of saturation, Sr; porosity, [Formula: see text]; and dry density, ρd) are very sensitive to changes in the applied confining pressures and their own swelling deformation (or shrinkage). The combination of these changes affects the sample’s effective gas permeability (Keff). For materials prepared at a relative humidity (RH) of 98%, Keff decreased from 10−16 to 10−20 m2 when Pc increased from 1 to 7 MPa. This means that gas-tightness can be obtained for a compacted bentonite–sand mixture when the materials experience a series of changes (e.g., w, Sr, [Formula: see text], and ρd). In addition, larger irreversible deformation (or hysteresis) was observed during the loading–unloading cycle for the sample with higher water content. This phenomenon may be attributed to larger interactions between the macrostructural and microstructural deformations and the decrease of preconsolidation pressure during hydration.

scholarly journals Gas flow unified measurement system for sequential measurement of gas diffusion and gas permeability of partially hydrated geosynthetic clay liners

2016 ◽  
Vol 53 (6) ◽  
pp. 1000-1012 ◽  
Author(s):  
Md A. Rouf ◽  
Abdelmalek Bouazza ◽  
Rao M. Singh ◽  
Will P. Gates ◽  
R. Kerry Rowe
Keyword(s):  
Water Content ◽  
Measurement System ◽  
Gas Flow ◽  
Gas Permeability ◽  
Gas Diffusion ◽  
Degree Of Saturation ◽  
Geosynthetic Clay Liners ◽  
Clay Liners ◽  
Sequential Measurement ◽  
Gravimetric Water Content

A gas flow unified measurement system (UMS-G) for sequential measurement of gas diffusion and gas permeability of geosynthetic clay liners (GCLs) under applied stress conditions (2 to 20 kPa) is described. Measurements made with the UMS-G are compared with measurements made with conventional experimental devices and are found to give similar results. The UMS-G removes the need to rely on two separate systems and increases further the reliability of the gas properties’ measurements. This study also shows that the gas diffusion and gas permeability reduce greatly with the increase of both gravimetric water content and apparent degree of saturation. The effect of applied stress on gas diffusion and gas permeability is found to be more pronounced at gravimetric water content greater than 60%. These findings suggest that at a nominal overburden stress of 20 kPa, the GCL used in the present investigation needs to be hydrated to 134% gravimetric water content (65% apparent degree of saturation) before gas diffusion and gas permeability drop to 5.5 × 10−11 m2·s−1 and 8.0 × 10−13 m·s−1, respectively, and to an even higher gravimetric water content (apparent degrees of saturation) at lower stress.

ANALYSIS OF GAS PERMEABILITY FOR LIQUID PHASE-SINTERED POROUS SiC COMPACT

2014 ◽  
Vol 17 (8) ◽  
pp. 705-713 ◽  
Author(s):  
Hikaru Maeda ◽  
Yoshihiro Hirata ◽  
Soichiro Sameshima ◽  
Taro Shimonosono
Keyword(s):  
Liquid Phase ◽  
Gas Permeability ◽  
Porous Sic

Dynamic Emergence of Nanostructure and Transport Properties in Perfluorinated Sulfonic Acid Ionomers

2020 ◽  
Author(s):  
Adlai Katzenberg ◽  
Debdyuti Mukherjee ◽  
Peter J. Dudenas ◽  
Yoshiyuki Okamoto ◽  
Ahmet Kusoglu ◽  
...  
Keyword(s):  
Rate Constant ◽  
Sulfonic Acid ◽  
Mass Fraction ◽  
Gas Permeability ◽  
Transport Processes ◽  
Segmental Mobility ◽  
The Matrix ◽  
Swelling Rate ◽  
Ion Conducting ◽  
Perfluorinated Sulfonic Acid

<p>Limitations in fuel cell electrode performance have motivated the development of ion-conducting binders (ionomers) with high gas permeability. Such ionomers have been achieved by copolymerization of perfluorinated sulfonic acid (PFSA) monomers with bulky and asymmetric monomers, leading to a glassy ionomer matrix with chemical and mechanical properties that differ substantially from common PFSA ionomers (e.g., Nafion™). In this study, we use perfluorodioxolane-based ionomers to provide fundamental insights into the role of the matrix chemical structure on the dynamics of structural and transport processes in ion-conducting polymers. Through <i>in-situ</i> water uptake measurements, we demonstrate that ionomer water sorption kinetics depend strongly on the properties and mass fraction of the matrix. As the PFSA mass fraction was increased from 0.26 to 0.57, the Fickian swelling rate constant decreased from 0.8 s<sup>-1</sup> to 0.2 s<sup>-1</sup>, while the relaxation rate constant increased from 3.1×10<sup>-3</sup> s<sup>-1</sup> to 4.0×10<sup>-3</sup>. The true swelling rate, in nm s<sup>-1</sup>, was determined by the chemical nature of the matrix; all dioxolane-containing materials exhibited swelling rates ~1.5 - 2 nm s<sup>-1</sup> compared to ~3 nm s<sup>-1</sup> for Nafion. Likewise, Nafion underwent relaxation at twice the rate of the fastest-relaxing dioxolane ionomer. Reduced swelling and relaxation kinetics are due to limited matrix segmental mobility of the dioxolane-containing ionomers. We demonstrate that changes in conductivity are strongly tied to the polymer relaxation, revealing the decoupled roles of initial swelling and relaxation on hydration, nanostructure, and ion transport in perfluorinated ionomers. </p>

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