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Geotechnical and Geological Engineering, 2018
Soil-water characteristic curve (SWCC) is an important unsaturated soil property relating the 19 water content of a soil to soil suction and it is conventionally measured using Tempe cell, 20 pressure plate and salt solution methods. However, these tests are tedious and time consuming. 21 The SWCC measurements using fast and efficient methods are required for engineering designs 22 Revised Manuscript Click here to download Manuscript Comparison of SWCC test Methods(9Feb18).doc Click here to view linked References such as excavation, slope protection, retaining wall and landfill cover designs. This paper 23 describes the testing procedures and apparatuses associated with rapid measurements of a 24 complete SWCC of a residual soil as obtained from combined measurements using a small-scale 25 centrifuge and dew point methods. The SWCC test results obtained using these alternative 26 methods were compared with the SWCC data from Tempe cell, pressure plate and salt solution 27 methods. Shrinkage tests were carried out in this study to incorporate the volume change of soil 28 into SWCC. The experimental data from all SWCC tests were evaluated using first order 29 analysis with 95 % confidence interval for determination of upper and lower bounds of SWCC. 30 The analysis results showed that the SWCC data obtained from tests using small-scale centrifuge 31 and dew point methods were in good agreement with those obtained from Tempe cell, pressure 32 plate and salt solution methods. This indicates that the combination of small-scale centrifuge and 33 dew point methods can be used to generate a complete curve of SWCC for the residual soil. In 34 addition, the time required to perform SWCC tests using the alternative methods is shorter than 35 the SWCC tests using the conventional methods.
Critical Review of the Methodologies Employed for Soil Suction Measurement
International Journal of Geomechanics, 2011
Modeling the behavior of unsaturated soils necessitates the measurement of soil suction and the establishment of its variation with the water content, which is commonly known as the soil-water characteristic curve (SWCC). Several methodologies have been developed for measuring either total suction ψ (sum of matric suction ψ m and osmotic suction ψ o ) or ψ m . While employing different methodologies for suction measurement, there is a possibility that various factors (viz., type of the soil, measurement methodology, range of the suction measurement, equilibration time, and presence of salts or contaminants in the soil) may influence the results and hence the SWCC. Therefore, it is essential to investigate the uniqueness of SWCC, determined by using some commonly adopted suction measurement methodologies. This study indicates that the SWCC established by adopting different methodologies may not be unique and is primarily influenced by the range of suction measurement. As such, it is essential to highlight the range of suction values involved for establishing the SWCC, to facilitate unambiguous modeling and to precisely understand the behavior of unsaturated soil.
5. Recent Developments in the Measurement of Wetting SWCC
The unsaturated soil behavior is of prime importance in many of the geotechnical and geoenvironmental applications. The characterization of the engineering behavior of unsaturated soil is entirely dependent on the soil-water characteristic curve (SWCC), which is a graphical relationship between water content (either gravimetric or volumetric) or degree of saturation and soil suction. For decades, experimental studies are performed to investigate the relationship between the soil suction and volumetric water content (SWCC). Most of the reported studies, discuss about drying SWCC due to the simplicity of its measurement. It must be noted that wetting SWCC is equally important for situations like seepage through unsaturated soil. With this in view, effort has been made in this paper to critically review the recent research outcomes in the measurement of wetting SWCC. The advantages and limitations associated with different measurement procedures are presented. This paper also describes a new approach for developing wetting SWCC with the help of a column test set up. The methodology has been demonstrated by determining the wetting SWCC of a locally available sandy soil.
Geotechnical Testing Journal, 2021
Devices that simultaneously facilitate controlling suction and applying a net stress on soil specimen provide soil-water characteristic curves (SWCCs) in terms of both the water content and degree of saturation, and volumetric deformations at various applied suctions. Such tests determine the water content of soil specimens based on the measured water volume changes at various applied suctions. However, studies have shown disagreements between the water volume-based calculated water content and the actual water content of soil specimens determined by the oven-drying method. Testing multiple soil specimens at predetermined suctions and measuring water content by the oven-drying method can overcome this but are a time-consuming approach. In this study, the impact of testing single and multiple soil specimens on the subsequently determined suction-water content and suction-degree of saturation SWCCs for the wetting process were studied. Statically compacted specimens of a sandy clay were used for establishing SWCCs using a suction control oedometer. Differences were noted between the calculated and measured water content and degree of saturation for an applied suction range of 0 to 95 kPa. Differences were noted between the SWCC fitting parameters obtained from the test results of single and multiple soil specimens. Statistical analysis suggested the differences between the results from single and multiple soil specimens testing were not significant. Corrections applied to the water volume change measurements were found to minimize these differences.
Comparison of Measured and PTF Predictions of SWCCs for Loess Soils in China
Geotechnical and Geological Engineering, 2010
There are significant advantages in using indirect pedo-transfer functions, (PTFs) for the estimation of unsaturated soil properties. The pedo-transfer functions can be used for the estimation of the soil–water characteristic curve (SWCC) which in turn is used for the estimation of other unsaturated soil properties. The accuracy of the indirect pedo-transfer function method for the estimation of the SWCC depends on the PTF and the equation used to best-fit the particle-size distribution (PSD) data. The objectives of this study are to: (1) evaluate the performance of the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation for best-fitting the particle-size distribution, (PSD) data, and, (2) compare the predictions made by two of the commonly used PTFs; namely, Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) and Fredlund et al. (Can Geotech J 39:1103–1117, 2002), for estimating the SWCC from the PSD. The authors used 258 measured PSDs and SWCC datasets from the Loess Plateau, China, for this study. The dataset consisted of 187 silt–loam soils, 41 loam soils, 11 silt–clay–loam soils, 10 sand–loam soils, 6 silt–clay soils, and 3 loam–sand soils. The SWCC and PSD datasets were measured using a Pressure Plate apparatus and the pipette method, respectively. The comparison between the estimated and measured particle-size distribution curves showed that the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation closely prepresented the PSD for all soils in the Loess Plateau, with a lower root mean square error (RMSE) of 0.869%. The comparison between the estimated and measured water contents at the same suction showed that the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF performed somewhat better than the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) function. The Fredlund et al. method had RMSE value of 0.039 cm3 cm−3 as opposed to 0.046 cm3 cm−3 for the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) method. The Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF produced the closest predictions for sand–loam, loam–sand, and loam soils, with a lower RMSE for gravimetric water content ranging from 0.006 to 0.036 cm3 cm−3. There were consistent over-estimations observed for silt–loam, silt–clay–loam, and slit–clay soils with RMSE values for gravimetric water content ranging from 0.037 to 0.043 cm3 cm−3. The measured and estimated air-entry values were closest when using the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF. The measured and estimated maximum slopes on the SWCC were closest when using the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) PTF.
Estimation of SWCC for Unsaturated Soils and Its Application to Design of Shallow Foundations
The importance of unsaturated soil mechanics stems from the fact that the majority of geotechnical engineering projects are taking place in unsaturated soil zones. Soil suction, especially matric suction, is controlling the unsaturated soil behavior. However, measurements and determination of the soil suction is still a concern for geotechnical engineers and researchers regarding its accuracy, practicality, cost, and reliability. In this study, the filter paper method (FPM) has been adopted as a secondary indirect measurement of the suction. Both total and matric suction were measured for three different mixtures of coarse soil (sand) and fine soil (industrial Bentonite/Montmorillonite) at two different saturation levels for each mixture. An extensive characterization has been conducted for the soil samples and, thereafter, samples were prepared at 95% of the maximum dry density (MDD) on wet and dry sides of optimum for suction measurements. The soil-water-characteristic/retention curve (SWCC/SWRC) was then completed for each sample using an estimation method reported in the literature. A new prediction model has been developed, in this study to determine a fitting parameter for estimating SWCC. Also, a review on the application of SWCC to design of shallow foundations has been presented in a simplified manner. Finally, recommendations for future work and conclusions were reported.
Influence of Drying and Wetting Cycles on SWCCs of Fine-Grained Soils
Journal of Testing and Evaluation, 2012
The soil-water characteristics curve (SWCC) is greatly influenced by the path that is followed for suction measurement (i.e., drying or wetting path) and the number of cycles of these paths to which the soil is exposed. To evaluate the influence of these parameters, drying-and wetting-path SWCCs of three fine-grained soils were developed for single and multiple cycles by employing the Aquasorp V R Isotherm generator. This device has been primarily employed for food products, powders, and amorphous materials for determination of their moisture sorption isotherm, which relates moisture content to water activity. As water activity can be mathematically related to soil suction, the Aquasorp V R can be used for developing the SWCC. Hence, demonstrating the potential of the Aquasorp V R for characterizing fine-grained soils becomes essential. The present study has been focused at highlighting the possible uncertainties associated with establishment of the SWCCs (both during drying and wetting paths) and the benefits and limitations of the Aquasorp V R in achieving these objectives. Furthermore, by employing mercury intrusion porosimetry (MIP), the significance of capillarity on soil suction, which in turn governs the SWCC, has been demonstrated.
Evaluation of Testing Methods for Suction-Volume Change of Natural Clay Soils
2017
Design and mitigation of infrastructure on expansive soils requires an understanding of unsaturated soil mechanics and consideration of two stress variables (net normal stress and matric suction). Although numerous breakthroughs have allowed geotechnical engineers to study expansive soil response to varying suction-based stress scenarios (i.e. partial wetting), such studies are not practical on typical projects due to the difficulties and duration needed for equilibration associated with the necessary laboratory testing. The current practice encompasses saturated "conventional" soil mechanics testing, with the implementation of numerous empirical correlations and approximations to obtain an estimate of true field response. However, it has been observed that full wetting rarely occurs in the field, leading to an over-conservatism within a given design when partial wetting conditions are ignored. Many researchers have sought to improve ways of ACKNOWLEDGMENTS I would like to give special thanks to Dr. Sandra L. Houston who provided me the opportunity to work with her on this study. She acted as my advisor, professor, role model, teammate, and friend. I would like to thank my two other committee members, Dr. Claudia Zapata and Dr. Edward Kavazanjian for their help and guidance during this process. I also very much appreciate Dr. William N. Houston for the many discussions and technical insight he provided to me during the course of this study. Much appreciation to Jeffry D. Vann, my boss, teammate, and friend, who provided me with all the resources and motivation to complete this study. Thank you to Alan Cuzme, Sai Singhar, Jeremy Minnick, Scott Morgan, and the rest of the Vann Engineering team for help with the field sampling and lab testing. I would also like to thank Manual Padilla and the team at GCTS in Tempe, AZ for the all technical support they provided for the oedometer pressure plate device and their quick turn around when new products were needed. I would like to thank Ronald McOmber and the team at CTL Thompson in Denver, CO for providing me with the additional soil samples used in this study.
2014
Characterization of the engineering behavior of<br> unsaturated soil is dependent on the soil-water characteristic curve<br> (SWCC), a graphical representation of the relationship between water<br> content or degree of saturation and soil suction. A reasonable<br> description of the SWCC is thus important for the accurate prediction<br> of unsaturated soil parameters. The measurement procedures for<br> determining the SWCC, however, are difficult, expensive, and timeconsuming.<br> During the past few decades, researchers have laid a<br> major focus on developing empirical equations for predicting the<br> SWCC, with a large number of empirical models suggested. One of<br> the most crucial questions is how precisely existing equations can<br> represent the SWCC. As different models have different ranges of<br> capability, it is essential to evaluate the precision of the SWCC<br> models used for each particul...
Estimation of unimodal water characteristic curve for gap-graded soil
Soils and Foundations, 2017
Soils with a bimodal grain-size distribution (gap-graded soils) can be associated with unimodal or bimodal soil-water characteristic curves (SWCCs). Many equations have been developed to estimate SWCCs using grain-size distribution curves to overcome the high cost and long duration of SWCC experiments. Most of the equations are limited to the estimation of the SWCCs of soils with a unimodal grain-size distribution. Few studies have been conducted on the estimation of unimodal SWCCs for gap-graded soils. In this paper, procedures, equations and computer codes are proposed for estimating the unimodal SWCCs of gap-graded soils. The proposed equations are found to perform well in estimating the unimodal SWCCs of gap-graded soils.