scholarly journals Performance Evaluation of Four-Parameter Models of the Soil-Water Characteristic Curve

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Siti Jahara Matlan ◽  
Muhammad Mukhlisin ◽  
Mohd Raihan Taha
Keyword(s):  
Soil Water ◽  
Characteristic Curve ◽  
Data Sets ◽  
Modified Model ◽  
Soil Water Characteristic Curve ◽  
Geoenvironmental Engineering ◽  
Wide Range ◽  
Soil Water Characteristic Curves ◽  
Model Equations ◽  
Exponential Variable

Soil-water characteristic curves (SWCCs) are important in terms of groundwater recharge, agriculture, and soil chemistry. These relationships are also of considerable value in geotechnical and geoenvironmental engineering. Their measurement, however, is difficult, expensive, and time-consuming. Many empirical models have been developed to describe the SWCC. Statistical assessment of soil-water characteristic curve models found that exponential-based model equations were the most difficult to fit and generally provided the poorest fit to the soil-water characteristic data. In this paper, an exponential-based model is devised to describe the SWCC. The modified equation is similar to those previously reported by Gardner (1956) but includes exponential variable. Verification was performed with 24 independent data sets for a wide range of soil textures. Prediction results were compared with the most widely used models to assess the model’s performance. It was proven that the exponential-based equation of the modified model provided greater flexibility and a better fit to data on various types of soil.

scholarly journals New approach to improve soil-water characteristic curve to reduce variation in estimation of unsaturated permeability function

2016 ◽  
Vol 53 (4) ◽  
pp. 717-725 ◽  
Author(s):  
Arezoo Rahimi ◽  
Harianto Rahardjo
Keyword(s):  
Soil Water ◽  
Distribution Curve ◽  
Characteristic Curve ◽  
New Approach ◽  
Soil Water Characteristic Curve ◽  
Permeability Function ◽  
Wide Range ◽  
Unsaturated Permeability ◽  
Complete Measurement ◽  
Data Points

The unsaturated permeability function is often estimated from the soil-water characteristic curve (SWCC) of a soil. A complete SWCC measurement can improve the estimation of the unsaturated permeability function. In most laboratories, the SWCC can be measured up to a suction of 100 kPa using a Tempe cell. However, complete measurement of the SWCC is an expensive and time-consuming task. Therefore, this paper presents a new approach to estimate SWCC data points beyond 100 kPa suction to complement the SWCC measured up to a suction of 100 kPa. The new SWCC is then used to estimate the unsaturated permeability function. The proposed approach uses knowledge of the grain-size distribution curve and measured SWCC data at 100 kPa suction to estimate the SWCC data points beyond 100 kPa suction. To verify the proposed procedure, SWCC tests were conducted over a wide range of suctions for coarse kaolin and a triaxial permeameter system was used to directly measure unsaturated permeability of the coarse kaolin. The proposed procedure is found to reduce the variation between unsaturated permeability functions estimated by various estimation models.

Equations for the entire soil-water characteristic curve of a volume change soil

2008 ◽  
Vol 45 (4) ◽  
pp. 443-453 ◽  
Author(s):  
Hung Q. Pham ◽  
Delwyn G. Fredlund
Keyword(s):  
Soil Water ◽  
Volume Change ◽  
Curve Fitting ◽  
Characteristic Curve ◽  
Engineering Practice ◽  
Soil Suction ◽  
Residual Soil ◽  
Soil Water Characteristic Curve ◽  
Geoenvironmental Engineering ◽  
Type Studies

Numerous curve-fitting equations have been proposed for soil-water characteristic curves. While these equations have been of considerable value in geotechnical and geoenvironmental engineering, the equations are not able to adequately fit gravimetric soil-water characteristic curve data over the entire range of soil suction for a soil that changes volume when suction is changed. Two new equations for the soil-water characteristic curve are presented in this paper. One equation has curve-fitting parameters that bear a meaningful relationship to conventional physical soil properties (e.g., air-entry value and residual soil suction), but the equation is somewhat complex. The equation is particularly useful for sensitivity type studies when undertaking computer modeling. The other equation is relatively simple to use and is developed as a conventional curve-fitting equation. The two equations are used to best-fit several soil datasets. Both equations perform well and can be used in research and engineering practice to define the gravimetric water content versus soil suction relationship for a soil exhibiting volume change.

Experimental Study on Soil Water Characteristic Curve of Compacted Unsaturated Soil

2010 ◽  
Vol 168-170 ◽  
pp. 1285-1288
Author(s):  
Dong Lin Wang
Keyword(s):  
Soil Water ◽  
Influencing Factors ◽  
Unsaturated Soils ◽  
Stress Condition ◽  
Characteristic Curve ◽  
External Stress ◽  
Method Of Least Squares ◽  
Soil Water Characteristic Curve ◽  
Triaxial Apparatus ◽  
Soil Water Characteristic Curves

Soil water characteristic curve is one of important topics of unsaturated soils. Pressure plate extractor and GDS unsaturated triaxial apparatus are used to study influencing factors including types of soils and net mean stress. Through method of least-squares, Fredlund five-parameter model were employed to fit soil-water characteristic curves. The results show that model provided a satisfactory fit to the experimental data. Through an analysis of influencing factors, we find that not only physical condition of samples but also external stress condition can affect the shape of soil water characteristic curve.

The Development of a One-Parameter Model for the Soil-Water Characteristic Curve in Loess Gully Regions

2012 ◽  
Vol 256-259 ◽  
pp. 488-493
Author(s):  
Xiao Yu Song ◽  
Huai You Li ◽  
Wen Juan Shi
Keyword(s):  
Soil Water ◽  
Hydraulic Properties ◽  
Characteristic Curve ◽  
Soil Samples ◽  
Soil Hydraulic Properties ◽  
Logarithmic Model ◽  
Soil Water Characteristic Curve ◽  
Soil Water Characteristic Curves ◽  
Best Fit ◽  
Gardner Model

It is important to understand soil hydraulic properties in order to predict the movement of water and solutes such as pollutants. To this end, 55 soil samples were collected from different areas of the Nanxiaohegou basin and used to generate soil-water characteristic curves. These were then fitted using the power-, exponential-, and logarithmic versions of the Gardner model; the logarithmic model yielded the best fit overall. The logarithmic model was further simplified to yield a one-parameter model for estimating the soil-water characteristic curve within the basin, and it was demonstrated that the value of the single parameter is dependent on the topography and usage of the land.

Statistical assessment of soil-water characteristic curve models for geotechnical engineering

2001 ◽  
Vol 38 (6) ◽  
pp. 1297-1313 ◽  
Author(s):  
W Scott Sillers ◽  
Delwyn G Fredlund
Keyword(s):  
Soil Water ◽  
Akaike Information Criterion ◽  
Characteristic Curve ◽  
Information Criterion ◽  
Soil Suction ◽  
Data Sets ◽  
Empirical Equations ◽  
Soil Water Characteristic Curve ◽  
The Relationship ◽  
Best Fit

A number of empirical equations have been proposed for the soil-water characteristic curve. A nonlinear, least squares method was used to determine best-fit parameters for several empirical equations that were best-fit to 230 water content versus soil suction data sets. In addition, two proposed correction methods to accommodate high soil suctions up to 1 000 000 kPa were applied to the various soil-water characteristic curve equations. The data sets of water content versus soil suction were arranged into one of the USDA soil classifications based on their relative amounts of sand, silt, and clay (only eight soil classifications had sufficient data for later analysis). The quality of fit for each model was compared using the Akaike Information Criterion. A series of conclusions were arrived at regarding (i) the relationship between two- and three-parameter equations, (ii) the relationship between exponential and sigmoidal type equations, and (iii) the value of correction factors for the high soil suction range.Key words: soil-water characteristic curve, unsaturated soil, soil suction, regression analysis, SWCC models, Akaike Information Criterion.

scholarly journals Soil-Water Characteristic Curve of Residual Soil from a Flysch Rock Mass

Geofluids ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-15 ◽  
Author(s):  
Josip Peranić ◽  
Željko Arbanas ◽  
Sabatino Cuomo ◽  
Matej Maček
Keyword(s):  
Rock Mass ◽  
Soil Water ◽  
Characteristic Curve ◽  
Detailed Examination ◽  
Residual Soil ◽  
Residual Soils ◽  
Infiltration Process ◽  
Soil Water Characteristic Curve ◽  
Wide Range ◽  
Flysch Rock Mass

Depending on the nature of the material and suction range, laboratory measurements of the soil-water characteristic curve (SWCC) can be time-consuming and expensive, especially for residual soils, in which a wide range of particle sizes and soil structures typically results in SWCCs that cover a wide range of suction. Investigations of the SWCCs of residual soil from flysch rock masses are rare, and so far, no results were presented in the literature which were obtained by performing measurements on undisturbed specimens. In this paper, a detailed examination of water retention characteristics is performed for a specific type of residual soil (CL) formed by the weathering of a flysch rock mass. Measurements performed by using different techniques and devices on intact specimens were successfully combined to obtain the SWCC during both drying and wetting processes, under different stress conditions, and from saturated to air-dried conditions. Used procedures are suitable for the determination of SWCCs of soils that undergo volume changes during the drying or the wetting process, since instantaneous volumetric water content can be determined. Results presented in this paper can be used to assess the influence of desaturation of the residual soil covering flysch slopes during dry summer periods by providing key-in material properties required to analyze the transient rainfall infiltration process.

Measurement of soil-water characteristic curves for fine-grained soils using a small-scale centrifuge

2002 ◽  
Vol 39 (5) ◽  
pp. 1209-1217 ◽  
Author(s):  
R M Khanzode ◽  
S K Vanapalli ◽  
D G Fredlund
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Characteristic Curve ◽  
Small Scale ◽  
Characteristic Curves ◽  
Pressure Plate ◽  
Soil Water Characteristic Curve ◽  
Fine Grained ◽  
Soil Water Characteristic Curves ◽  
Plate Apparatus

Considerably long periods of time are required to measure soil-water characteristic curves using conventional equipment such as pressure plate apparatus or a Tempe cell. A commercially available, small-scale medical centrifuge with a swinging type rotor assembly was used to measure the soil-water characteristic curves on statically compacted, fine-grained soil specimens. A specimen holder was specially designed to obtain multiple sets of water content versus suction data for measuring the soil-water characteristic curve at a single speed of rotation of the centrifuge. The soil-water characteristic curves were measured for three different types of fine-grained soils. The three soils used in the study were processed silt (liquid limit, wL = 24%; plasticity index, Ip = 0; and clay = 7%), Indian Head till (wL = 35.5%, Ip = 17%, and clay = 30%), and Regina clay (wL = 75.5%, Ip = 21%, and clay = 70%). The soil-water characteristic curves for the above soils were measured in 0.5, 1, and 2 days, respectively, using the centrifuge technique for suction ranges from 0 to 600 kPa. Time periods of 2, 4–6, and 16 weeks were required for measuring the soil-water characteristic curves for the same soils using a conventional pressure plate apparatus. There is reasonably good agreement between the experimental results obtained by the centrifuge and the pressure plate methods. The results of this study are encouraging as soil-water characteristic curves can be measured in a reduced time period when using a small-scale centrifuge.Key words: unsaturated soils, soil-water characteristic curve, centrifuge technique, soil suction, matric suction, water content.

Investigating structural stability using the soil water characteristic curve

2002 ◽  
Vol 42 (3) ◽  
pp. 291 ◽  
Author(s):  
K. Barlow ◽  
D. Nash
Keyword(s):  
Soil Water ◽  
Soil Structure ◽  
Agricultural Land ◽  
Characteristic Curve ◽  
Soil Cores ◽  
Undisturbed Soil ◽  
Soil Water Characteristic Curve ◽  
Soil Water Characteristic Curves ◽  
Intact Soil Cores ◽  
The Stability

Soil physical properties, including infiltration, strength, water storage and aeration, affect the productivity of agricultural land. This paper investigated the stability of soil structure to chemical disruption, using the soil water characteristic curve. The soil water characteristic was determined twice on intact soil cores of an acidic mesotrophic, red Ferrosol (Gn4.11) and an acidic, eutrophic, grey Dermosol (Gn4.51). Saturated NaCl or deionised water was used to wet the soil cores between each determination. Despite the variability associated with undisturbed soil cores, significant differences were detected in the soil water characteristic curves both within and between soil types. The ability to detect differences in the soil structure of the Ferrosol and Dermosol, both Emerson class 8, suggests this technique could be used to determine the chemical stability of soils with minimal mechanical disruption of the structure.

How to predict hydraulic conductivity of unsaturated soils from an incomplete soil water characteristic curve?

2020 ◽  
Author(s):  
Xingwei Ren ◽  
Qidong Fang ◽  
Xiaojun Chen
Keyword(s):  
Hydraulic Conductivity ◽  
Soil Water ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Ground Surface ◽  
Experimental Conditions ◽  
Flow Process ◽  
Soil Water Characteristic Curve ◽  
Wide Range ◽  
Extensive Experimental Data

<p>Unsaturated soils are those in which pore is filled partially with water and partially with air. They are the most relevant porous medium to human activities, and cover almost all the soils near the ground surface. Hydraulic conductivity (HC) is one of the most important and useful properties of unsaturated soils in numerous studies, including governing flow process, settlement of soil foundations, migration of groundwater and gas hydrate. Unfortunately, direct measurement of HC for unsaturated soils is very difficult with high uncertainty due to its nature of complexity and limited experimental conditions. Thus, indirect estimation of HC from soil water characteristic curve (SWCC) becomes an alternative way and being widely used all over the world.</p><p>Because of the difficulty to reach high suction at the residual state of unsaturated soils, however, the SWCC obtained by laboratory experiments is often incomplete, which will lead to an unreliable estimation of hydraulic conductivity. However, no study has been published on how to estimate hydraulic conductivity of unsaturated soils with incomplete SWCC. In response to this situation, an innovative method was proposed based on the classical van Genuchten model and Mualem model. The proposed method was evaluated by extensive experimental data from existing literature and proved to have an excellent performance in predicting a complete SWCC for a wide range of soils. Also, it exhibits certain superiority in predicting hydraulic conductivity. The limitations of the proposed method were comprehensively discussed, and its corresponding improvement strategies were also addressed. This paper presents a practical way to obtain a more reliable hydraulic conductivity from incomplete SWCC.</p>

Evaluating dual porosity of pelletized diatomaceous earth using bimodal soil-water characteristic curve functions

2001 ◽  
Vol 38 (1) ◽  
pp. 53-66 ◽  
Author(s):  
Craig A Burger ◽  
Charles D Shackelford
Keyword(s):  
Soil Water ◽  
Diatomaceous Earth ◽  
Pore Space ◽  
Characteristic Curve ◽  
Coarse Grained ◽  
Dual Porosity ◽  
Scanning Electron Micrographs ◽  
Characteristic Curves ◽  
Soil Water Characteristic Curve ◽  
Soil Water Characteristic Curves

Soil-water characteristic curve data for specimens containing either ~1 mm or ~2 mm diameter pellets of processed diatomaceous earth are measured using a variety of methods (Tempe cell, pressure plate, filter paper, and chilled-mirror psychrometer). The measured soil-water characteristic curve data are bimodal, reflecting both the microscopic porosity region within the individual pellets, or intrapellet porosity, and the macroscopic porosity region between the pellets, or interpellet porosity. The bimodal distributions are consistent with scanning electron micrographs that show the existence of microscopic pores within each pellet, and the relatively high total porosities (0.725 and 0.764) for the coarse-grained diatomaceous earth specimens. The measured soil-water characteristic curve data are fit with modified forms of the Brooks–Corey, van Genuchten, and Fredlund–Xing soil-water characteristic curve functions to account for the bimodal shapes of the measured data. The average microscopic porosities resulting from the curve fits represent 45.0 and 47.9% of the total porosities for the two diatomaceous earth materials. These percentages of microscopic pore space are consistent with the product literature value of approximately 50% for the same materials based on mercury intrusion porosimetry. Thus, the results illustrate the application of bimodal soil-water characteristic curve functions for determining the microscopic and macroscopic portions of the total porosity of dual-porosity media, such as pelletized diatomaceous earth.Key words: bimodal soil-water characteristic curves, diatomaceous earth, dual porosity, macroporosity, microporosity, soil-water characteristic curves (SWCC), soil suction.

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