FUNCTIONAL MODELS TO PREDICT AIR PERMEABILITY COEFFICIENT FROM WATER CHARACTERISTIC CURVE OF UNSATURATED SOILS

The air permeability coefficient has a high correlation with the water content of municipal solid waste. In this study, continuous drying methodology using a tension meter was employed to construct the soil water characteristic curve of municipal solid waste (M-SWCC). The municipal solid waste air permeability test was conducted by a newly designed apparatus. The measured M-SWCC was well reproduced by the van Genuchten (V-G) model and was used to predict the parameters of typical points in M-SWCC, including saturated water content, field capacity, residual water content and water content at the inflection point. It was found that the M-SWCC was significantly influenced by void ratio. The final evaporation and test period of M-SWCC increase with the increase in void ratio of municipal solid waste. The evolution of air permeability coefficient with water content of municipal solid waste depicted three distinct characteristic stages. It was observed that the water contents that corresponded to the two cut-off points of the three stages were residual water content and water content at the inflection point, respectively. The air permeability coefficient of municipal solid waste decreased with the increase of the water content from zero to the residual water content. The air permeability coefficient was almost invariable when the water content increased from residual water content to the water content at the inflection point. When the water content of municipal solid waste exceeded the water content at the inflection point, the air permeability coefficient sharply decreased with the increase of water content.

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A UNIFIED FRACTAL MODEL FOR PERMEABILITY COEFFICIENT OF UNSATURATED SOIL

Fractals ◽

10.1142/s0218348x19400127 ◽

2019 ◽

Vol 27 (01) ◽

pp. 1940012 ◽

Cited By ~ 4

Author(s):

GAOLIANG TAO ◽

XIAOKANG WU ◽

HENGLIN XIAO ◽

QINGSHENG CHEN ◽

JIANCHAO CAI

Keyword(s):

Relative Permeability ◽

Unsaturated Soil ◽

Permeability Coefficient ◽

Unsaturated Soils ◽

Fractal Theory ◽

Characteristic Curve ◽

Fractal Model ◽

Computational Effort ◽

Model Parameters ◽

Mechanical Coupling

Due to the significant challenges in the measurements, evaluation of permeability coefficient for unsaturated soil is of immense importance for investigating the seepage and hydro-mechanical coupling problems of unsaturated soil. However, the predictions of existing typical models reveal significance divergence for permeability coefficient of unsaturated soils even under identical conditions. In particular, the existing models are greatly restricted in their practical application due to their complexity in the form of integral expressions that require significant computational effort. Here, a simplified unified model is presented to estimate the relative permeability coefficient. First, a fractal-form of soil–water characteristic curve (SWCC) is derived from fractal theory. Then, on the basis of the proposed SWCC models, the classical models (i.e. Childs and Collis-George (CCG) model, Burdine model, Mualem model and Tao and Kong model, respectively) for evaluating the permeability coefficient of unsaturated soil are converted to be presented in fractal forms. It is interestingly found that the fractal forms of these models are enormously similar. Based on these observations, a simplified unified fractal model for the relative permeability coefficient of unsaturated soil is proposed, where only two parameters (i.e. fractal dimension and air-entry value) are included, thereby significantly reducing the computational efforts. The detailed procedure for determining model parameters is elaborated. The accuracy of this model is verified by comparing its predictions with the experimental data for over 12 types of unsaturated soils. The results highlight that, compared with existing models, the proposed model would be much more efficiently used for estimating the relative permeability coefficient of unsaturated soils, thereby facilitating its application for investigating the associated seepage and hydro-mechanical coupling problems in practice.

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Simple Graphical Prediction of Relative Permeability of Unsaturated Soils under Deformations

Fractal and Fractional ◽

10.3390/fractalfract5040153 ◽

2021 ◽

Vol 5 (4) ◽

pp. 153

Author(s):

Gaoliang Tao ◽

Qing Wang ◽

Qingsheng Chen ◽

Sanjay Nimbalkar ◽

Yinjie Peng ◽

...

Keyword(s):

Relative Permeability ◽

Unsaturated Soil ◽

Permeability Coefficient ◽

Unsaturated Soils ◽

Sandy Loam ◽

Characteristic Curve ◽

Prediction Method ◽

Unified Model ◽

Application Range ◽

Before And After

At present, there are only a few existing models that can be used to predict the relative permeability of unsaturated soil under deformations, and the calculation process is relatively complex. In order to fit the measured value of the relative permeability coefficient of unsaturated soil before deformation, this work employs the simplified unified model of the relative permeability coefficient of unsaturated soil, and it obtains the index λ before deformation of the soil. In addition, the value of index λ remains unchanged before and after deformation. Based on the actual measured value of the soil–water characteristic curve before deformation, the air-entry value prediction model is used to predict the air-entry value of soil with different initial void ratios. The relative permeability coefficient of unsaturated soil is then conveniently predicted using the graphical method in combination with the simplified unified model. The method is validated by using the test data of silt loam, sandy loam, and unconsoildated sand. The results show that the predicted results are consistent with the measured values. The prediction method in this paper is simple and overcomes the limitations associated with the determination of the index λ. It expands the application range of the unsaturated relative permeability coefficient model while improving the accuracy of predictions.

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Soil Strength Reduction Method Induced by Variation of Water Content

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.170-173.847 ◽

2012 ◽

Vol 170-173 ◽

pp. 847-852

Author(s):

Peng Ming Jiang ◽

Zhong Lei Yan ◽

Peng Li

Keyword(s):

Slope Stability ◽

Unsaturated Soil ◽

Unsaturated Soils ◽

Characteristic Curve ◽

Strength Reduction ◽

Actual State ◽

Soil Slope ◽

Simple Method ◽

The Common ◽

The Stability

As the complexity of unsaturated soil theory, and it must have a long test period when we study the unsaturated soils, so the conventional design analysis software does not provide such analysis, so we can imagine that such a slope stability analysis does not accurately reflect the actual state of the slope. Based on the known soil moisture content，this paper use the soil water characteristic curve and strength theory of unsaturated soil to calculate the strength reduction parameters of soil which can calculate the stability of the soil slope when using the common calculation method. It is noticeable that this method can be extended and applied if we establish regional databases for this simple method, and these databases can improve the accuracy of the calculation of slope stability.

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Prediction of air permeability coefficient and water-vapor resistance of 3D textile layer

Journal of the Textile Institute ◽

10.1080/00405000.2021.1883237 ◽

2021 ◽

pp. 1-9

Author(s):

Aušra Gadeikytė ◽

Aušra Abraitienė ◽

Rimantas Barauskas

Keyword(s):

Water Vapor ◽

Permeability Coefficient ◽

Air Permeability

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Measurement of Soil Suction and Soil-Water Characteristics of Bentonite-Sand Mixtures

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 1 ◽

10.1115/omae2010-20980 ◽

2010 ◽

Author(s):

Pan Hu ◽

Qing Yang ◽

Maotian Luan

Keyword(s):

Soil Water ◽

Vapor Phase ◽

Unsaturated Soils ◽

Characteristic Curve ◽

Phase Method ◽

Soil Suction ◽

Compacted Bentonite ◽

Water Characteristics ◽

Wide Range ◽

High Level

The soil-water characteristic curve (SWCC) is a widely used experimental means for assessing fundamental properties of unsaturated soils for a wide range of soil suction values. The study of SWCC is helpful because some properties of unsaturated soils can be predicted from it. Nowadays, much attention has been paid to the behaviours of highly compacted bentonite-sand mixtures used in engineering barriers for high level radioactive nuclear waste disposal. It is very important to study the various performances of bentonite-sand mixtures in order to insure the safety of high-level radioactive waste (HLW) repository. After an introduction to vapor phase method and osmotic technique, a laboratory study has been carried out on compacted bentonite-sand mixtures. The SWCC of bentonite-sand mixtures has been obtained and analyzed. The results show that the vapor phase method and osmotic technique is suitable to the unsaturated soils with high and low suction.

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The air permeability of composite fiber material

Perspektivnye Materialy ◽

10.30791/1028-978x-2021-1-42-48 ◽

2021 ◽

Vol 1 ◽

pp. 42-48

Author(s):

T. A. Leshchenko ◽

◽

N. V. Chernousova ◽

A. V. Dedov ◽

◽

...

Keyword(s):

Composite Materials ◽

Permeability Coefficient ◽

Pore Space ◽

Fiber Material ◽

Composite Fiber ◽

Air Permeability ◽

Rubber Content ◽

Limited Mobility ◽

Fibrous Matrix ◽

Composite Fiber Material

The air permeability of composite materials obtained by impregnating a non-woven needle-punched cloth with latex was investigated. The permeability of composite materials with different rubber content was estimated by the coefficient of air permeability at a pressure drop of 49 and 100 Pa. The dependence of the air permeability coefficient on the degree of impregnation of the fabric showed that at 15 – 20 % of the rubber content, the maximum air permeability coefficient is observed, and when the degree of impregnation increases, the air permeability coefficient decreases. The process of forming a porous structure of composite materials and its influence on air transport is considered. The increase of the coefficient of permeability is explained by the fixation of the fibers of the surface layer with limited mobility under the action of air flow, and a reduction in the coefficient of air permeability by reducing pore space and an increase in fiber matrix composite materials in the process of sushi-Ki-impregnated material. The air permeability of composite materials is determined by the ratio between the processes of increasing the volume of the fibrous matrix and reducing porosity when filling the space between the portages with rubber particles. A model is proposed for calculating the coefficient of breathability of composite materials of known density.

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A relationship describing the shear strength of unsaturated soils

Canadian Geotechnical Journal ◽

10.1139/t98-102 ◽

1999 ◽

Vol 36 (2) ◽

pp. 363-368 ◽

Cited By ~ 33

Author(s):

Daud W Rassam ◽

David J Williams

Keyword(s):

Shear Strength ◽

Soil Water ◽

Nonlinear Regression ◽

Unsaturated Soils ◽

Characteristic Curve ◽

Three Dimensional ◽

Matric Suction ◽

Linear Increase ◽

Soil Water Characteristic Curve ◽

Stress Dependent

A relationship describing the shear-strength profile of a desiccating soil deposit is essential for the purpose of analysis, especially when a numerical method is adopted where each zone in a discretised grid is assigned an elevation-dependent shear-strength value. The matric-suction profile of a desiccating soil deposit is nonlinear. Up to the air-entry value, an increase in matric suction is associated with a linear increase in shear strength. Beyond air entry, as the soil starts to desaturate, a nonlinear increase in shear strength occurs. The soil-water characteristic curve is stress dependent, as is the shear-strength gain as matric suction increases. In this paper, a three-dimensional, nonlinear regression analysis showed that a power-additive function is suitable to describe the variation of the shear strength of unsaturated soils with matric suction. The proposed function incorporates the effect of normal stress on the contribution of matric suction to the shear strength.Key words: air-entry value, matric suction, nonlinear regression, soil-water characteristic curve, tailings, unsaturated shear strength.

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