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Field Suction and Effect of Cracking in Highly Plastic Clay

TL;DR: In this paper, a study was conducted to determine field suction values as well as the effect of cracking on the hydraulic properties of compacted highly plastic clays, and the results indicated that cracking has a significant effect on the soil-water retention curve and the hydraulic conductivity of the highly plastic clay under unsaturated conditions.
Abstract: A study was conducted to determine field suction values as well as the effect of cracking on the hydraulic properties of compacted highly plastic clays. This investigation consisted of an experimental program involving a series of instrumented soil column tests on highly plastic clay prepared under controlled compaction conditions and subjected to evaporation, infiltration, and a second evaporation stage. During both evaporation and infiltration stages, water content and suction profiles were measured. Analysis was conducted using the results of the experimental program to determine the effect of cracking on the hydraulic properties of the soil. This analysis indicates that cracking has a significant effect on the soil-water retention curve and the hydraulic conductivity of the compacted highly plastic clay under unsaturated conditions. The results of this analysis allow determination of field suction values and depth of moisture fluctuation. This study is complimented with slope stability analyses, evaluation of the recurrence rate of failures, and an overview of site visits conducted in this study.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors investigated the soil-atmosphere interaction by conducting physical model test in the laboratory and by performing numerical analysis using data from an experimental site, which showed that evaporation is a heat consuming process.

60 citations

Dissertation
02 Nov 2009
TL;DR: In this paper, a chambre environnementale a ete developpee pour etudier le comportement de l'interface sol-atmosphere durant l'infiltration and l'evaporation.
Abstract: Une chambre environnementale a ete developpee pour etudier le comportement de l'interface sol-atmosphere durant l'infiltration et l'evaporation. Un volume d'environ un metre cube d'argile verte de Romainville a ete mis en place par compactage. Pres de cent capteurs ont ete utilises pour assurer un suivi tres large des parametres du sol (succion, teneur en eau, temperature, gonflement a la surface) et de l'air (vitesse du vent, humidite relative, temperature). La temperature a la surface ainsi que la fissuration due au sechage ont ete egalement suivies. Les mesures pendant la premiere phase d'humidification ont permis la determination de la conductivite hydraulique en fonction de la succion et de la courbe de retention d'eau du sol. La deuxieme phase comporte quatre essais de sechage dont deux pour l'evaluation du taux d'evaporation potentiel PE et deux autres pour la determination du rapport du taux d'evaporation reel AE au taux d'evaporation potentiel PE. Les resultats obtenus ont permis l'elaboration d'une nouvelle approche de calcul de PE, et le developpement d'une nouvelle approche de calcul de AE en tenant compte de la fissuration en surface du sol.

18 citations

01 Apr 2009
TL;DR: A feasibility study was performed to determine the potential advantages of characterizing the swelling properties of highly plastic clay using a geotechnical centrifuge as discussed by the authors, which allowed for the characterization of the soil within 24 hours of the start of testing.
Abstract: A feasibility study was performed to determine the potential advantages of characterizing the swelling properties of highly plastic clay using a geotechnical centrifuge. This study consisted of an experimental program involving a series of tests in a small and large centrifuge in which water was ponded atop compacted clay specimens, flown up to speed, and the specimen’s height was monitored with time. This method allowed for the characterization of the swelling properties of the soil within 24 hours of the start of testing. Traditional free-swell testing to achieve the same level of characterization required approximately 30 days for the highly plastic clay evaluated in the study. This new centrifuge methodology for evaluating the swelling potential of clay was found to produce comparable results to traditional testing in a fraction of the time. Centrifuge testing of highly plastic clays will allow the Texas Department of Transportation to acquire a speedy characterization of the swelling characteristics of highly plastic clays by direct measurement of swelling rather than by the use of correlations between swelling and index properties or suction.

6 citations

Dissertation
23 Oct 2013
TL;DR: In this article, a model of the processus de fissuration des sols fins is presented, which is based on the concept of fissures of dessiccation.
Abstract: L’objectif de ce travail est d’etudier l’effet des fissures de dessiccation sur le comportement thermo-hydro-mecanique des sols argileux sensibles au phenomene de retrait. Ce travail inclut une etude experimentale caracterisant l’influence des fissures sur le sechage des sols fins ainsi qu’une etude numerique comprenant une modelisation du processus dans le but de presenter l’impact des fissures sur le comportement thermo-hydrique d’un milieu argileux non sature. L’etude experimentale comprend des experiences de sechage realisee en laboratoire sur des echantillons de sol intacts et fissures ou l’evolution de la teneur en eau a ete suivie. Les processus lies la formation de nouvelles fissures ainsi qu’a la propagation des fissures sont aussi discutes.Une modelisation numerique du processus de fissuration des sols fins est ensuite presentee. Dans cette etude, une analyse detaillee de l’influence des fissures sur l’interaction sol-atmosphere est presentee. Un modele numerique bidimensionnel de l’interaction sol- atmosphere tenant compte de la presence des fissures a ete developpe. Ce modele prend en compte le couplage thermo-hydrique d’un milieu argileux non sature. Dans cette etude, on a montre l’impact des fissures sur le developpement de la succion, sur la variation de la teneur en eau ainsi que sur la valeur d’entree de l’air. L’influence des fissures sur l’evolution du tassement du sol est egalement presentee. Cette etude propose aussi une approche simple pour la prise en compte des fissures dans l’interaction sol-atmosphere.Dans la derniere partie de ce travail, l’influence des fissures sur le comportement mecanique des sols fins est presentee et discutee.

3 citations

01 Aug 2013
TL;DR: In this paper, a novel centrifuge-testing device was developed for characterization of expansive soils, which are the source of major pavement design and maintenance problems across the state of Texas, and testing protocols were developed for use of a small centrifuge device to provide direct measurement of the vertical swelling of clays.
Abstract: A novel centrifuge-testing device was developed for characterization of expansive soils, which are the source of major pavement design and maintenance problems across the state. Specifically, testing protocols were developed for use of a small centrifuge device to provide direct measurement of the vertical swelling of clays. In this test, soil samples are subjected to water infiltration during a comparatively short testing period. The centrifuge approach is well suited for pavement design because it provides not only one data point for a single normal stress but the entire relationship between vertical strains and vertical stresses. This feature represents a significant advantage over conventional swelling tests, which are prohibitively long; in addition, each conventional test provides the vertical strain for one vertical stress. Consequently, this approach is particularly well suited for use with the Potential Vertical Raise (PVR) approach. The objective of this project is to quantify the benefits and implement the new centrifuge technology for characterization of expansive clays in Texas. This research team will achieve this objective by implementing the laboratory procedure developed as part of Research Project 0-6048 using multiple clay sources, developing a spreadsheet with swelling curves (vertical strain versus normal stress) for relevant high-plasticity clays in Texas, incorporating the use of swelling curves obtained using centrifuge technology into the PVR methodology, and developing training material that includes examples of practical problems for calculation of the PVR using actual swelling curves and actual subgrade profiles.
References
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Journal ArticleDOI
TL;DR: Van Genuchten et al. as mentioned in this paper proposed a closed-form analytical expression for predicting the hydraulic conductivity of unsaturated soils based on the Mualem theory, which can be used to predict the unsaturated hydraulic flow and mass transport in unsaturated zone.
Abstract: A new and relatively simple equation for the soil-water content-pressure head curve, 8(h), is described in this paper. The particular form of the equation enables one to derive closedform analytical expressions for the relative hydraulic conductivity, Kr, when substituted in the predictive conductivity models of N.T. Burdine or Y. Mualem. The resulting expressions for Kr(h) contain three independent parameters which may be obtained by fitting the proposed soil-water retention model to experimental data. Results obtained with the closed-form analytical expressions based on the Mualem theory are compared with observed hydraulic conductivity data for five soils with a wide range of hydraulic properties. The unsaturated hydraulic conductivity is predicted well in four out of five cases. It is found that a reasonable description of the soil-water retention curve at low water contents is important for an accurate prediction of the unsaturated hydraulic conductivity. Additional Index Words: soil-water diffusivity, soil-water retention curve. van Genuchten, M. Th. 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44:892-898. T USE OF NUMERICAL MODELS for simulating fluid flow and mass transport in the unsaturated zone has become increasingly popular the last few years. Recent literature indeed demonstrates that much effort is put into the development of such models (Reeves and Duguid, 1975; Segol, 1976; Vauclin et al., 1979). Unfortunately, it appears that the ability to fully characterize the simulated system has not kept pace with the numerical and modeling expertise. Probably the single most important factor limiting the successful application of unsaturated flow theory to actual field problems is the lack of information regarding the parameters entering the governing transfer equations. Reliable estimates of the unsaturated hydraulic conductivity are especially difficult to obtain, partly because of its extensive variability in the field, and partly because measuring this parameter is time-consuming and expensive. Several investigators have, for these reasons, used models for calculating the unsaturated conductivity from the more easily measured soil-water retention curve. Very popular among these models has been the Millington-Quirk method (Millington and Quirk, 1961), various forms of which have been applied with some success in a number of studies (cf. Jackson et al., 1965; Jackson, 1972; Green and Corey, 1971; Bruce, 1972). Unfortunately, this method has the disadvantage of producing tabular results which, for example when applied to nonhomogeneous soils in multidimensional unsaturated flow models, are quite tedious to use. Closed-form analytical expressions for predicting 1 Contribution from the U. S. Salinity Laboratory, AR-SEA, USDA, Riverside, CA 92501. Received 29 June 1979. Approved 19 May I960. 'Soil Scientist, Dep. of Soil and Environmental Sciences, University of California, Riverside, CA 92521. The author is located at the U. S. Salinity Lab., 4500 Glenwood Dr., Riverside, CA 92502. the unsaturated hydraulic conductivity have also been developed. For example, Brooks and Corey (1964) and Jeppson (1974) each used an analytical expression for the conductivity based on the Burdine theory (Burdine, 1953). Brooks and Corey (1964, 1966) obtained fairly accurate predictions with their equations, even though a discontinuity is present in the slope of both the soil-water retention curve and the unsaturated hydraulic conductivity curve at some negative value of the pressure head (this point is often referred to as the bubbling pressure). Such a discontinuity sometimes prevents rapid convergence in numerical saturated-unsaturated flow problems. It also appears that predictions based on the Brooks and Corey equations are somewhat less accurate than those obtained with various forms of the (modified) Millington-Quirk method. Recently Mualem (1976a) derived a new model for predicting the hydraulic conductivity from knowledge of the soil-water retention curve and the conductivity at saturation. Mualem's derivation leads to a simple integral formula for the unsaturated hydraulic conductivity which enables one to derive closed-form analytical expressions, provided suitable equations for the soil-water retention curves are available. It is the purpose of this paper to derive such expressions using an equation for the soil-water retention curve which is both continuous and has a continuous slope. The resulting conductivity models generally contain three independent parameters which may be obtained by matching the proposed soil-water retention curve to experimental data. Results obtained with the closedform equations based on the Mualem theory will be compared with observed data for a few soils having widely varying hydraulic properties. THEORETICAL Equations Based on Mualem's Model The following equation was derived by Mualem (1976a) for predicting the relative hydraulic conductivity (Kr) from knowledge of the soil-water retention curve

22,781 citations

Journal ArticleDOI
TL;DR: The dependence of the dielectric constant, at frequencies between 1 MHz and 1 GHz, on the volumetric water content is determined empirically in the laboratory as discussed by the authors, and the effect of varying the texture, bulk density, temperature, and soluble salt content on this relationship was also determined.
Abstract: The dependence of the dielectric constant, at frequencies between 1 MHz and 1 GHz, on the volumetric water content is determined empirically in the laboratory. The effect of varying the texture, bulk density, temperature, and soluble salt content on this relationship was also determined. Time-domain reflectometry (TDR) was used to measure the dielectric constant of a wide range of granular specimens placed in a coaxial transmission line. The water or salt solution was cycled continuously to or from the specimen, with minimal disturbance, through porous disks placed along the sides of the coaxial tube. Four mineral soils with a range of texture from sandy loam to clay were tested. An empirical relationship between the apparent dielectric constant Ka and the volumetric water content θv, which is independent of soil type, soil density, soil temperature, and soluble salt content, can be used to determine θv, from air dry to water saturated, with an error of estimate of 0.013. Precision of θv to within ±0.01 from Ka can be obtained with a calibration for the particular granular material of interest. An organic soil, vermiculite, and two sizes of glass beads were also tested successfully. The empirical relationship determined here agrees very well with other experimenters' results, which use a wide range of electrical techniques over the frequency range of 20 MHz and 1 GHz and widely varying soil types. The results of applying the TDR technique on parallel transmission lines in the field to measure θv versus depth are encouraging.

4,855 citations

Journal ArticleDOI
TL;DR: In this paper, an evaluated compilation of equilibrium relative humidity in air versus temperature from pure phase to approximately 105 pascal (1 atm) in pressure is presented for 28 binary saturated aqueous solutions.
Abstract: An evaluated compilation of equilibrium relative humidities in air versus temperature from pure phase to approximately 105 pascal (1 atm) in pressure is presented for 28 binary saturated aqueous solutions. The relative humidities of the solutions range from about 3 to 98 percent. Using a data base from 21 separate investigations comprising 1106 individual measurements, fits were made by the method of least squares to regular polynomial equations with two through four coefficients. Equations and tables are presented along with the estimated uncertainties in the correlated results. Research, hygrometer calibration, testing and material conditioning often require the accurate control of humidity in a working space. The common methods of controlling the humidity accurately use either a humidity generator (1A)1 or the equilibration of a closed space with a chemical system (IB) which produces the desired equilibrium vapor pressure. Humidity generators tend to be expensive and complex whereas equilibration with chemical systems that provide fixed points is a relatively inexpensive and simple method of humidity control. Among the chemical systems used for this purpose are aqueous sulphuric acid solutions, glycerine and water solutions and single and binary salt solutions. Each such solution offers a degree of humidity adjustment that can be achieved by changing its concentration. On the other hand, special problems are associated with the use of solu- tions because their concentrations must be measured and controlled. Not only must the concentration of the solution be determined initially but the presence of any humidity sources or sinks in the controlled space and even the initial equilibra- tion process of the space can alter the solution concentration. An especially useful method of humidity control by chemi- cal system involves the use of binary saturated aqueous solutions (primarily of single salts) in which the solute is highly non-volatile. At any temperature, the concentration of a saturated solu- tion is fixed and does not have to be determined. By provid- ing excess solute, the solution will remain saturated even in the presence of modest sources or sinks. Where the solute is a solid in the pure phase, it is easy to determine that there is indeed saturation. Due to the ease of its use, this is a popular method of humidity control. Since a given saturated salt solution provides only one relative humidity (RH) at any desired temperature, a different relative humidity must be achieved by selecting another appropriate salt. Though much data on saturated salt solu-

3,503 citations

Journal ArticleDOI
TL;DR: In this article, a theory is presented that develops the functional relationships among saturation, pressure difference, and permeabilities of air and liquid in terms of hydraulic properties of partially saturated porous media, based only on the capillary pressure-desaturation relationships for porous media.
Abstract: Following the Burdine approach, based on a model developed by Wyllie and Spangler, a theory is presented that develops the functional relationships among saturation, pressure difference, and permeabilities of air and liquid in terms of hydraulic properties of partially saturated porous media. The theory is based only on the capillary pressure-desaturation relationships for porous media. Procedures for determining these hydraulic properties from capillary pressure-desaturation curves are described. Permeabilities to the wetting and nonwetting phases as a function of capillary pressure and saturation are predicted from the experimentally determined hydraulic properties. The results for all media studied are in close agreement with the theory.

1,953 citations