scholarly journals Simple Graphical Prediction of Relative Permeability of Unsaturated Soils under Deformations

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.

A UNIFIED FRACTAL MODEL FOR PERMEABILITY COEFFICIENT OF UNSATURATED SOIL

Fractals ◽  
2019 ◽  
Vol 27 (01) ◽  
pp. 1940012 ◽  
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.

scholarly journals Simplified Relation Model of Soil Saturation Permeability Coefficient and Air-Entry Value and Its Application

2021 ◽  
Vol 5 (4) ◽  
pp. 180
Author(s):  
Gaoliang Tao ◽  
Zhijia Wu ◽  
Wentao Li ◽  
Yi Li ◽  
Heming Dong
Keyword(s):  
Permeability Coefficient ◽  
Sandy Loam ◽  
Characteristic Curve ◽  
Prediction Method ◽  
Fractal Model ◽  
Silty Clay ◽  
Clay Loam ◽  
Silty Clay Loam ◽  
Proportionality Constant ◽  
The Relationship

Based on the Tao and Kong (TK) model and the fractal model of the soil–water characteristic curve, a simplified model of the relationship between the saturated permeability coefficient and the air-entry value is established in this study: ks = k0ψa−2. It is shown that the saturated permeability coefficient of soil is determined by its maximum pore size. In order to facilitate the mutual prediction of saturation permeability coefficient and air-entry value, based on the data of five types of soil in the UNSODA database, the comprehensive proportionality constant k0 of the five types of soil were obtained: sand k0 = 0.03051; clay k0 = 0.001878; loam k0 = 0.001426; sandy loam k0 = 0.009301; and silty clay loam k0 = 0.0007055. Based on the obtained comprehensive proportionality constant k0 and the relationship model between saturated permeability coefficient and air intake value, the air-entry value of five kinds of soils in the existing literature and the SoilVision database were calculated. Comparing the calculated air-entry value with the measured one, the results showed that the model simplifies the traditional air-entry value prediction method to some extent and can effectively predict the air-entry value of different types of soil. On the whole, the model better predicts the air-entry value for sandy, clay, and silty clay loam than loam and sandy loam.

Soil Strength Reduction Method Induced by Variation of Water Content

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.

Method for Quick Prediction of Hydraulic Conductivity and Soil-Water Retention of Unsaturated Soils

2018 ◽  
Vol 2672 (52) ◽  
pp. 108-117 ◽  
Author(s):  
Shaoyang Dong ◽  
Yuan Guo ◽  
Xiong (Bill) Yu
Keyword(s):  
Finite Element ◽  
Hydraulic Conductivity ◽  
Soil Properties ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Characteristic Curve ◽  
Soil Water Retention

Hydraulic conductivity and soil-water retention are two critical soil properties describing the fluid flow in unsaturated soils. Existing experimental procedures tend to be time consuming and labor intensive. This paper describes a heuristic approach that combines a limited number of experimental measurements with a computational model with random finite element to significantly accelerate the process. A microstructure-based model is established to describe unsaturated soils with distribution of phases based on their respective volumetric contents. The model is converted into a finite element model, in which the intrinsic hydraulic properties of each phase (soil particle, water, and air) are applied based on the microscopic structures. The bulk hydraulic properties are then determined based on discharge rate using Darcy’s law. The intrinsic permeability of each phase of soil is first calibrated from soil measured under dry and saturated conditions, which is then used to predict the hydraulic conductivities at different extents of saturation. The results match the experimental data closely. Mualem’s equation is applied to fit the pore size parameter based on the hydraulic conductivity. From these, the soil-water characteristic curve is predicted from van Genuchten’s equation. The simulation results are compared with the experimental results from documented studies, and excellent agreements were observed. Overall, this study provides a new modeling-based approach to predict the hydraulic conductivity function and soil-water characteristic curve of unsaturated soils based on measurement at complete dry or completely saturated conditions. An efficient way to measure these critical unsaturated soil properties will be of benefit in introducing unsaturated soil mechanics into engineering practice.

The Trial Research of Soil-Water Characteristic Curves of Unsaturated Soil and its Engineering Application

2012 ◽  
Vol 170-173 ◽  
pp. 3050-3053
Author(s):  
Cui Ran Liu ◽  
Jin Jun Guo
Keyword(s):  
Soil Water ◽  
Unsaturated Soil ◽  
Permeability Coefficient ◽  
Characteristic Curve ◽  
Engineering Application ◽  
Engineering Properties ◽  
Confining Pressures ◽  
Soil Water Characteristic Curves ◽  
Matrix Suction ◽  
Water Contents

With the improved triaxial equipment, the tests of research of the relationships between matrix suction and water content are performed And based on the test data, the curves between matrix suction and water contents under different confining pressures are drawn and the change rule between them are analyzed. And then the function between them is simulated out. Through the soil-water characteristic curve, the permeability coefficient of unsaturated soil can be calculated and the shear strength of unsaturated soil can be predicted. These results are important to research the engineering properties of unsaturated soil.

Model for the prediction of shear strength with respect to soil suction

1996 ◽  
Vol 33 (3) ◽  
pp. 379-392 ◽  
Author(s):  
S K Vanapalli ◽  
D G Fredlund ◽  
D E Pufahl ◽  
A W Clifton
Keyword(s):  
Shear Strength ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Experimental Studies ◽  
Matric Suction ◽  
Glacial Till ◽  
Soil Suction ◽  
Soil Water Characteristic Curve

Experimental studies on unsaturated soils are generally costly, time-consuming, and difficult to conduct. Shear strength data from the research literature suggests that there is a nonlinear increase in strength as the soil desaturates as a result of an increase in matric suction. Since the shear strength of an unsaturated soil is strongly related to the amount of water in the voids of the soil, and therefore to matric suction, it is postulated that the shear strength of an unsaturated soil should also bear a relationship to the soil-water characteristic curve. This paper describes the relationship between the soil-water characteristic curve and the shear strength of an unsaturated soil with respect to matric suction. Am empirical, analytical model is developed to predict the shear strength in terms of soil suction. The formulation makes use of the soil-water characteristic curve and the saturated shear strength parameters. The results of the model developed for predicting the shear strength are compared with experimental results for a glacial till. The shear strength of statically compacted glacial till specimens was measured using a modified direct shear apparatus. Specimens were prepared at three different water contents and densities (i.e., corresponding to dry of optimum, and wet of optimum conditions). Various net normal stresses and matric suctions were applied to the specimens. There is a good correlation between the predicted and measured values of shear strength for the unsaturated soil. Key words: soil-water characteristic curve, shear strength, unsaturated soil, soil suction, matric suction.

Volume–mass unsaturated soil constitutive model for drying–wetting under isotropic loading–unloading conditions

2011 ◽  
Vol 48 (2) ◽  
pp. 280-313 ◽  
Author(s):  
Hung Q. Pham ◽  
Delwyn G. Fredlund
Keyword(s):  
Constitutive Model ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Research Literature ◽  
Degree Of Saturation ◽  
Soil Conditions ◽  
Constitutive Relationships ◽  
Proposed Model ◽  
Wide Range

A rigorous volume–mass constitutive model is proposed for the representation of drying–wetting under isotropic loading–unloading conditions for unsaturated soils. The proposed model utilizes concepts arising from soil physics and geotechnical engineering research and requires readily obtainable soils data for soil properties. The model can be used to predict void ratio and water content constitutive relationships (and therefore degree of saturation) for a wide range of unsaturated soils. Various stress paths (i.e., loading–unloading and drying–wetting) can be simulated, and hysteresis associated with the soil-water characteristic curve is taken into account. Two closed-form equations for the volume–mass constitutive relationships are presented for soils starting from slurry conditions. A number of test results (i.e., from experimental programs reported in the research literature) were used during the verification of the proposed volume–mass constitutive model. The volume–mass constitutive model captures key unsaturated soil conditions such as air-entry value, water-entry value, and residual conditions. The proposed model appears to satisfactorily predict unsaturated soil behavior for soils ranging from low compressible sands to high compressible clays.

Predicting the permeability function for unsaturated soils using the soil-water characteristic curve

1994 ◽  
Vol 31 (4) ◽  
pp. 533-546 ◽  
Author(s):  
D.G. Fredlund ◽  
Anqing Xing ◽  
Shangyan Huang
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Degree Of Saturation ◽  
Residual Water ◽  
Soil Water Characteristic Curve ◽  
Coefficient Of Permeability ◽  
Permeability Function

The coefficient of permeability for an unsaturated soil is primarily determined by the pore-size distribution of the soil and can be predicted from the soil-water characteristic curve. A general equation, which describes the soil-water characteristic curve over the entire suction range (i.e., from 0 to 106 kPa), was proposed by the first two authors in another paper. This equation is used to predict the coefficient of permeability for unsaturated soils. By using this equation, an evaluation of the residual water content is no longer required in the prediction of the coefficient of permeability. The proposed permeability function is an integration form of the suction versus water content relationship. The proposed equation has been best fit with example data from the literature where both the soil-water characteristic curve and the coefficient of permeability were measured. The fit between the data and the theory was excellent. It was found that the integration can be done from zero water content to the saturated water content. Therefore, it is possible to use the normalized water content (volumetric or gravimetric) or the degree of saturation data versus suction in the prediction of the permeability function. Key words : coefficient of permeability, soil-water characteristic curve, unsaturated soil, water content, soil suction.

The Experimental Study of Permeability Coefficient of Unsaturated Soil

2011 ◽  
Vol 71-78 ◽  
pp. 1158-1162
Author(s):  
Cui Ran Liu ◽  
Peng Li He ◽  
Huai Feng Tong
Keyword(s):  
Unsaturated Soil ◽  
Permeability Coefficient ◽  
Unsaturated Soils ◽  
Indirect Method ◽  
Direct Method ◽  
Silty Clay ◽  
Test Results ◽  
Triaxial Apparatus ◽  
Technical Requirements ◽  
Direct Measurements

Due to the complexity and variability of unsaturated soil, the permeability property of unsaturated soils is clearly different from that of saturated soil. And because the test equipment is more complex and technical requirements are higher and diachronic cycle is longer, the researches related are slow. Using the triaxial apparatus of unsaturated soil, the direct and indirect experiments to study the permeability coefficient of unsaturated silty clay are done. Test results show that the permeability coefficient of unsaturated soil can be done by the indirect method and direct method. Not only the direct measurements of the permeability coefficient of unsaturated soil are realized through this trial, but also the reliability of indirect method is proved.

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