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Journal ArticleDOI

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

01 Aug 1994-Canadian Geotechnical Journal (NRC Research Press Ottawa, Canada)-Vol. 31, Iss: 4, pp 533-546
TL;DR: The coefficient of permeability for unsaturated soil is primarily determined by the pore-size distribution of the soil and can be predicted from the soil-water characteristic curve as mentioned in this paper.
Abstract: 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 eq...
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24 Jul 2012
TL;DR: This paper explains the nature of each of the previous challenges to the implementation of unsaturated soil mechanics, and the determination of indirect techniques for the estimation of uns saturated soil property functions.
Abstract: Unsaturated soil mechanics has rapidly become a part of geotechnical engineering practice as a result of solutions that have emerged to a number of key problems (or challenges). The solutions have emerged from numerous research studies focusing on issues that have a hindrance to the usage of unsaturated soil mechanics. The primary challenges to the implementation of unsaturated soil mechanics can be stated as follows: (1) The need to understand the fundamental, theoretical behavior of an unsaturated soil; (2) the formulation of suitable constitutive equations and the testing for uniqueness of proposed constitutive relationships; (3) the ability to formulate and solve one or more nonlinear partial differential equations using numerical methods; (4) the determination of indirect techniques for the estimation of unsaturated soil property functions, and (5) in situ and laboratory devices for the measurement of a wide range of soil suctions. This paper explains the nature of each of the previous challenges and...

562 citations

Journal ArticleDOI
TL;DR: In this article, the authors evaluate the more popular unsaturated soil mechanics equations and show that all the equations can be derived from a single generic form, which performs very well for all soil types.
Abstract: Practical applications of unsaturated soil mechanics still lag behind the state-of-the-art knowledge The main stumbling block is the time-consuming processes involved in the measurement of the unsaturated soil parameters required for the constitutive models Recent research has shown that the soil-water characteristic curves of a soil can be used in the establishment of a number of the unsaturated soil parameters In many applications, it has become obvious that a satisfactory equation for describing the soil-water characteristic curve will simplify the determination of the soil parameters Over the years a number of equations have been suggested Most of these equations have limited success depending on soil types This paper evaluates the more popular equations that have been suggested and shows that all the equations can be derived from a single generic form One equation has been identified that performs very well for all soil types If this equation is in common usage, useful databases on unsaturated soil parameters can be more easily established for practical applications of unsaturated soil mechanics

454 citations

Journal ArticleDOI
TL;DR: The water retention curve (WRC) has become a key material function to define the unsaturated behavior of soils and other particulate media as discussed by the authors, and in many instances, it can be useful to have an estimate o...
Abstract: The water retention curve (WRC) has become a key material function to define the unsaturated behavior of soils and other particulate media. In many instances, it can be useful to have an estimate o...

295 citations


Additional excerpts

  • ...As direct measurement of ku can be difficult, time consuming, and costly, it is customary to use, as a starting point, some relationship between θ and ψ to estimate the ku function (e.g., Mualem 1976, 1986; Fredlund et al. 1994), because the WRC can be evaluated more easily than ku in the laboratory or in the field....

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Journal ArticleDOI
Abstract: We present an integrated analysis of bank erosion in a high-curvature bend of the gravel bed Cecina River (central Italy). Our analysis combines a model of fluvial bank erosion with groundwater flow and bank stability analyses to account for the influence of hydraulic erosion on mass failure processes, the key novel aspect being that the fluvial erosion model is parameterized using outputs from detailed hydrodynamic simulations. The results identify two mechanisms that explain how most bank retreat usually occurs after, rather than during, flood peaks. First, in the high curvature bend investigated here the maximum flow velocity core migrates away from the outer bank as flow discharge increases, reducing sidewall boundary shear stress and fluvial erosion at peak flow stages. Second, bank failure episodes are triggered by combinations of pore water and hydrostatic confining pressures induced in the period between the drawdown and rising phases of multipeaked flow events.

289 citations


Cites methods from "Predicting the permeability functio..."

  • ...In summary, this procedure consists of using a range of empirical relations defined for each type of material [Green and Corey, 1971; Van Genuchten, 1980; Fredlund et al., 1994] based on the grain size distribution of each layer of sediment....

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  • ...In summary, this procedure consists of using a range of empirical relations defined for each type of material [Green and Corey, 1971; Van Genuchten, 1980; Fredlund et al., 1994 ] based on the grain size distribution of each layer of sediment....

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Journal ArticleDOI
TL;DR: In this paper, the relative importance of soil properties, rainfall intensity, initial water table location and slope geometry in inducing instability of a homogenous soil slope under different rainfall was investigated through a series of parametric studies.
Abstract: Rainfall-induced slope failure is a common geotechnical problem in the tropics where residual soils are abundant. Although the significance of rainwater infiltration in causing landslides is widely recognized, there have been different conclusions as to the relative roles of antecedent rainfall to landslides. The relative importance of soil properties, rainfall intensity, initial water table location and slope geometry in inducing instability of a homogenous soil slope under different rainfall was investigated through a series of parametric studies. Soil properties and rainfall intensity were found to be the primary factors controlling the instability of slopes due to rainfall, while the initial water table location and slope geometry only played a secondary role. The results from the parametric studies also indicated that for a given rainfall duration, there was a threshold rainfall intensity which would produce the global minimum factor of safety. Attempts have also been made to relate the findings from this study to those observed in the field by other researchers. Results of this parametric study clearly indicated that the significance of antecedent rainfall depends on soil permeability.

281 citations

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: In this article, a simple analytic model is proposed which predicts the unsaturated hydraulic conductivity curves by using the moisture content-capillary head curve and the measured value of the hydraulic conductivities at saturation.
Abstract: A simple analytic model is proposed which predicts the unsaturated hydraulic conductivity curves by using the moisture content-capillary head curve and the measured value of the hydraulic conductivity at saturation. It is similar to the Childs and Collis-George (1950) model but uses a modified assumption concerning the hydraulic conductivity of the pore sequence in order to take into account the effect of the larger pore section. A computational method is derived for the determination of the residual water content and for the extrapolation of the water content-capillary head curve as measured in a limited range. The proposed model is compared with the existing practical models of Averjanov (1950), Wyllie and Gardner (1958), and Millington and Quirk (1961) on the basis of the measured data of 45 soils. It seems that the new model is in better agreement with observations.

6,529 citations

Journal ArticleDOI
01 Nov 1931-Physics
TL;DR: In this article, the authors used Darcey's law to derive the equation K∇2ψ+∇K·∇ψ +g∂K/∂z=−ρsA∆ψ/∆t for the capillary conduction of liquids in porous mediums.
Abstract: The flow of liquids in unsaturated porous mediums follows the ordinary laws of hydrodynamics, the motion being produced by gravity and the pressure gradient force acting in the liquid. By making use of Darcey's law, that flow is proportional to the forces producing flow, the equation K∇2ψ+∇K·∇ψ+g∂K/∂z=−ρsA∂ψ/∂t may be derived for the capillary conduction of liquids in porous mediums. It is possible experimentally to determine the capillary potential ψ=∫dp/ρ, the capillary conductivity K, which is defined by the flow equation q=K(g−▿ψ), and the capillary capacity A, which is the rate of change of the liquid content of the medium with respect to ψ. These variables are analogous, respectively, to the temperature, thermal conductivity, and thermal capacity in the case of heat flow. Data are presented and application of the equations is made for the capillary conduction of water through soil and clay but the mathematical formulations and the experimental methods developed may be used to express capillary flow ...

5,340 citations

Journal ArticleDOI
TL;DR: In this paper, a nonlinear, least squares computer program is used to determine the best-fit parameters for experimental data presented in the literature, based on the assumption that the shape of the soil-water characteristic curve is dependent upon the pore-size distribution.
Abstract: The soil-water characteristic curve can be used to estimate various parameters used to describe unsaturated soil behaviour. A general equation for the soil-water characteristic curve is proposed. A nonlinear, least-squares computer program is used to determine the best-fit parameters for experimental data presented in the literature. The equation is based on the assumption that the shape of the soil-water characteristic curve is dependent upon the pore-size distribution of the soil (i.e., the desaturation is a function of the pore-size distribution). The equation has the form of an integrated frequency distribution curve. The equation provides a good fit for sand, silt, and clay soils over the entire suction range from 0 to 106 kPa. Key words : soil-water characteristic curve, pore-size distribution, nonlinear curve fitting, soil suction, water content.

2,644 citations


"Predicting the permeability functio..." refers background or methods in this paper

  • ...The detailed non-linear curve-fitting algorithm was outlined by Fredlund and Xing (1994)....

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  • ...Equation [11] fits the experimental data well in the entire suction range from 0 to 106 kPa (Fredlund and Xing 1994)....

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  • ...A general equation describing the soil-water characteristic curve over the entire suction range (i.e., 0 to 106 kPa) was proposed by Fredlund and Xing (1994): [11] [ ]{ } θ ψ θ ψ = + C a s n m( ) ln e ( )/ where: e is the natural number, 2.71828, a is approximately the air-entry value of the soil,…...

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  • ...…m is a parameter that is related to the residual water content, and C(ψ) is a correcting function defined as C C C r r ( ) ln ln( / ) ψ ψ = − + + 1 1 1 1000000 where C r is a constant related to the matric suction corresponding to the residual water content θ r (Fredlund and Xing 1994)....

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  • ...The equation for the soil-water characteristic curve proposed by Fredlund and Xing (1994) was found to be effective in the prediction of the coefficient of permeability for unsaturated soils....

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