scholarly journals A Fractal Model to Interpret Porosity-Dependent Hydraulic Properties for Unsaturated Soils

2019 ◽  
Vol 2019 ◽  
pp. 1-13 ◽  
Author(s):  
Annan Zhou ◽  
Yang Fan ◽  
Wen-Chieh Cheng ◽  
Junran Zhang
Keyword(s):  
Fractal Dimension ◽  
Soil Water ◽  
Pore Volume ◽  
Unsaturated Soils ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Pore Radius ◽  
Fractal Model ◽  
Soil Water Retention ◽  
Hydraulic Behaviour

This paper presents a simple fractal model to quantify the effects of initial porosity on the soil-water retention curve and hydraulic conductivity of unsaturated soils. In the proposed conceptual model, the change of maximum pore radius, which largely determines the change of the air-entry value, is directly related to the fractal dimension of pore volume (D) and porosity change. The hydraulic properties of unsaturated soils are then governed by the maximum pore radius, the fractal dimension of pore volume (D), and the fractal dimension of drainable pore volume (Dd ≤ D). The new fractal model removes the empirical fitting parameters that have no physical meaning from existing models for porosity-dependent water retention and hydraulic behaviour and employs parameters of fractal dimensions that are intrinsic to the nature of the fractal porous materials. The proposed model is then validated against experimental data from the literature on soil-water retention behaviour and unsaturated conductivity.

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.

scholarly journals Evolution of the soil water retention curve based on plastic volumetric strain

2020 ◽  
Vol 195 ◽  
pp. 02016
Author(s):  
J. Kodikara ◽  
C. Jayasundara
Keyword(s):  
Soil Water ◽  
Unsaturated Soils ◽  
Water Retention ◽  
Void Ratio ◽  
Volumetric Strain ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Retention Curve ◽  
Plastic Volumetric Strain

The water retention behaviour of soil can be defined as the relationship between the degree of saturation (or water content) and suction at a constant temperature, which characterises the hydraulic behaviour of unsaturated soils, normally represented as the soil water retention curve (SWRC). The SWRC is commonly measured at nominal net stress by initially saturating a soil specimen and then subjecting it to drying and wetting paths, resulting in major drying and wetting curves. However, there is evidence that during these major drying and wetting paths and initial saturation, soil can undergo volumetric deformation with changes in void ratio, sometimes plastically. Therefore, for coupling the SWRC with mechanical behaviour, the dependency of SWRC on other state variables such as void ratio has been proposed. In this paper, an approach to defining SWRC for a particular plastic volumetric strain is presented within the generalised MPK model. The SWRC evolves as soil is subjected to wet/dry cycles, eventually approaching drying and wetting curves relevant to an environmentally-stabilised state. The performance of this model is demonstrated by the simulation of the loading/unloading/drying/wetting paths followed in a laboratory experiment. In addition, the evolution of the commonly-considered major drying and wetting curves is simulated, highlighting key features of the environmentally-stabilised line..

Experiments and interpretations on unsaturated hydraulic properties using water retention tests based on the membrane in Korea

2020 ◽  
Author(s):  
Seboong Oh ◽  
Sungjin Kim ◽  
Kwang Ik Son
Keyword(s):  
Unsaturated Soils ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Void Ratio ◽  
Water Retention Curve ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Huge Amount ◽  
Retention Curve ◽  
Hydraulic Behavior

<p>In unsaturated soils, the soil water retention curve (SWRC) is most important in the fundamental hydraulic properties. In order to measure SWRCs through an alternative method in Korea, high air entry disks were replaced by micro membranes. Micro membranes are thin in which the air entry value is around 100kPa. Tests with the membrane are fast to reduce the duration of infiltration through the high air entry disk.</p><p>The water retention curves using the membrane were compared with the data using high air entry disks from the volumetric pressure plate extractor and Tempe pressure cell for samples of various sites. As a result, the SWRCs using the membrane were very similar for most cases and the micro membrane was verified as a useful tool to measure SWRCs.</p><p>The unsaturated hydraulic behavior could be measured easily using the membrane than ceramic disks and the huge amount of data could have been obtained in Korea. Using DB of SWRCs, the hydraulic properties were interpreted based on the parameters of the van Genuchten SWRC model. The void ratio and density are correlated to SWRCs under the same classification soil.</p><p><strong>Acknowledgements</strong> This research is supported by grant from Korean NRF (2019R1A2C1003604) and MOE (79608), which are greatly appreciated.</p>

Measurement of soil hydraulic properties of structured and repacked soils

2021 ◽  
Author(s):  
Urša Pečan ◽  
Luka Žvokelj ◽  
Jure Ferlin ◽  
Vesna Zupanc ◽  
Marina Pintar
Keyword(s):  
Soil Water ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Soil Samples ◽  
Measuring System ◽  
Soil Hydraulic Properties ◽  
Soil Water Retention ◽  
Undisturbed Soil ◽  
Soil Hydraulic ◽  
Low Tension

<p>Soil hydraulic properties provide important information about soil behavior under unsaturated and saturated conditions. Often sampling of undisturbed soils is not possible and soil samples have to be repacked for laboratory analysis. The HYPROP® measuring system (METERgroup, Munich, Germany) is a convenient method for determination of soil water retention characteristics and unsaturated hydraulic conductivity of undisturbed soil samples. It measures the matric potential of the saturated and drying soil sample using two tensiometers placed at different depths. Although the tensiometers are based on a new design that theoretically withstands cavitation at higher tension values, they are still considered to operate in the low tension range. Since soil water retention properties in the low tension range are strongly influenced by soil structure and pore size distribution, we were interested in the changes in hydraulic properties when measured on disturbed and then repacked samples, and undisturbed soil samples. Therefore, we investigated the soil hydraulic properties of three different soil types using the evaporation method on undisturbed and repacked samples. The results provide important insights for the interpretation of the results when the collection of undisturbed samples is not possible, and for designing laboratory experiments with repacked soils.</p>

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