Soil Unsaturated Hydraulic Conductivity Research Articles

Soil Air Permeability Modeling and Its Use for Predicting Unsaturated Soil Hydraulic Conductivity

Core Ideas Ka(θ) was modeled by considering a similar phenomenon between water and air flows in soil medium. Kw(θ) and Ka(θ) were theoretically linked by considering a similar intrinsic permeabilities for both water and air. The proposed models were tested with laboratory‐measured data showing reasonable accuracy. Since the direct measurement of soil hydraulic conductivity [Kw(θ)] is time consuming and difficult, several methods have been suggested for its prediction. However, their application still requires some kind of direct or experimental measurement, even after calibration. Considering much easier measurement of the air permeability [Ka(θ)] and the water and air flows in the soil medium, several attempts have been made to link Kw(θ) and Ka(θ), most of which have used Ka(θ) to predict the saturated hydraulic conductivity (Ks). The current research was aimed to model the air permeability and evaluate its application for Kw(θ) prediction. In this regard, laboratory measurements were conducted for Kw(θ) and Ka(θ) at different soil moisture contents (θ). Then, we introduced a semitheoretical model and evaluated it using measured data. Results showed that the proposed model can predict Kw(θ), with an average evaluation error of 3.69% and average R2 of 0.88. Regarding the fast and nondestructive measurement of Ka(θ) compared with Kw(θ), the proposed model seems to be more practical to characterize unsaturated soil hydraulic conductivity and can improve the accuracy and efficiency of Kw(θ) estimation.

Application of fitting parameters in best fit equation

Soil-water characteristic curve (SWCC) contains key information for the application of unsaturated soil mechanics principles to engineering practice. SWCC variables such as air-entry value, residual suction and residual saturation are commonly referred to for estimation of other unsaturated soil properties. Though there are clear definitions for these SWCC variables, it is difficult to measure them directly in laboratory and these SWCC variables are commonly estimated from SWCC. Hydraulic conductivity of unsaturated soil is the major property that controls water flow in soil. The laboratory measurement of hydraulic conductivity is time consuming and costly. Therefore, hydraulic conductivity is also commonly estimated from SWCC. Normally, SWCC is represented by a best fit equation which is typically governed by few fitting parameters. These fitting parameters can be obtained from a best fit procedure and are proven to be dependent on each other. Fredlund and Xing’s (1994) equation is one of the popular equations commonly used by researchers and there are only three fitting parameters such as “a”, “n”, “m” in this equation. Correlation equations between SWCC variables, hydraulic conductivity and the fitting parameters such as “a”, “n” and “m” are presented in this paper. In addition, the variability in the determined SWCC variables and hydraulic conductivity due to the variation in these fitting parameters is also discussed in this paper.

Unsaturated Soil Mechanics Principles to Remove and Replace Mitigation for Expansive Clays

The efficacy of removal and replacement as a mitigation alternative for expansive soil is discussed in view of numerical unsaturated flow/deformation results. Observations with respect to selection of depth and replacement soil type (similar, more, or less permeable than underlying expansive clay) are presented in the context of unsaturated flow and stress/deformation principles. Comparisons are made between various remove and replace options on the basis of extent and degree of wetting (changes in soil suction) and on ground surface total and differential movements. Selection of optimal removal and replacement depth and replacement material type requires consideration of unsaturated flow principles and understanding of the role of both net normal stress and matric suction in unsaturated soil response. Complexities in the unsaturated flow process which impact the efficacy of the remove and replace method are primarily because of the highly nonlinear nature of the unsaturated soil storage function (SWCC) and hydraulic conductivity function. Further, because the unsaturated hydraulic conductivity of soils depends on the value of soil suction, placement water content of the replacement layer has significant effect on performance. The net result is that the impact of various remove and replace options is not always intuitive. The findings presented, although not encompassing of all possible removal and replacement configurations or surface flux conditions, set the stage for application of remove and replace mitigation methods based on fundamental unsaturated soil mechanics principles.

Prediction of unsaturated soil hydraulic conductivity using air permeability: Regression approach

A close correlation between water conductivity (<italic>K(θ)</italic>) and air permeability (<italic>K</italic><sub><italic>a</italic></sub>), measured at various water contents, is expected due to tight dependence of water filled porosity to air filled porosity of soils. Finding such a relation will greatly facilitate the prediction of unsaturated water conductivity (<italic>K(θ)</italic>). So, the purpose of the current investigation was to find out if a reliable relation or function between the two permeabilities can be established. In this regard, <italic>K(θ)</italic> and <italic>K</italic><sub><italic>a</italic></sub> were measured by pressure plate outflow and variable head methods, respectively, at the range of 0 to -100 kPa matric potential (<italic>ψ</italic><sub><italic>m</italic></sub>). A linear regression function between relative water conductivity (<italic>K</italic><sub><italic>r</italic></sub>(<italic>θ</italic>)) and <italic>K</italic><sub><italic>a</italic></sub> (<italic>LogK</italic><sub><italic>r</italic></sub> (<italic>θ</italic>)=<italic>a</italic>+<italic>bLogK</italic><sub><italic>a</italic></sub>) with the correlation coefficient (<italic>R</italic>) from 0.884 to 0.999 were established for the 22 examined soils. The overall <italic>R</italic> for 128 data pairs (<italic>K</italic><sub><italic>r</italic></sub>(<italic>θ</italic>) and <italic>K</italic><sub><italic>a</italic></sub>) became 0.821 (being significant at <italic>P</italic><0.01) with the slope (<italic>b</italic>) of -2.54 and intercept (<italic>a</italic>) of -10.93. For the comparison propose <italic>K</italic><sub><italic>r</italic></sub>(<italic>θ</italic>) were also predicted from RETC using experimental SMC data and van Genuchten and Brooks-Corey models. The reliability of the <italic>K</italic><sub><italic>r</italic></sub>(<italic>θ</italic>) prediction from <italic>K</italic><sub><italic>a</italic></sub> based on root mean square error (RMSE), geometric mean error ratio (GMER), and geometric standard deviation of error ratio (GSDER) criteria became considerable greater than those predicted from the two mentioned models.

The role of the initial soil water content in the determination of unsaturated soil hydraulic conductivity using a tension infiltrometer

The role of the initial soil water content in the determination of unsaturated soil hydraulic conductivity using a tension infiltrometer

Determining hydraulic properties of a loam soil by alternative infiltrometer techniques

Testing infiltrometer techniques to determine soil hydraulic properties is necessary for specific soils. For a loam soil, the water retention and hydraulic conductivity predicted by the BEST (Beerkan Estimation of Soil Transfer parameters) procedure of soil hydraulic characterization was compared with data collected by more standard laboratory and field techniques. Six infiltrometer techniques were also compared in terms of saturated soil hydraulic conductivity, Ks. BEST yielded water retention values statistically similar to those obtained in the laboratory and Ks values practically coinciding with those determined in the field with the pressure infiltrometer (PI). The unsaturated soil hydraulic conductivity measured with the tension infiltrometer (TI) was reproduced satisfactorily by BEST only close to saturation. BEST, the PI, one-potential experiments with both the TI and the mini disk infiltrometer (MDI), the simplified falling head (SFH) technique and the bottomless bucket (BB) method yielded statistically similar estimates of Ks, differing at the most by a factor of three. Smaller values were obtained with longer and more soil-disturbing infiltration runs. Any of the tested infiltration techniques appears usable to obtain the order of magnitude of Ks at the field site, but the BEST, BB and PI data appear more appropriate to characterize the soil at some stage during a rainfall event. Additional investigations on both similar and different soils would allow development of more general procedures to apply infiltrometer techniques for soil hydraulic characterization. Copyright © 2015 John Wiley & Sons, Ltd.

One-Dimensional Coupled Infiltration and Deformation in Unsaturated Soils Subjected to Varying Rainfall

AbstractAssuming that the water content and hydraulic conductivity of unsaturated soil are exponential functions of the pressure head, Green’s function is used to obtain analytical solutions to one-dimensional coupled rainfall infiltration and deformation in unsaturated soils under varying surface rainfall flux. The analytical solution considers varying flux and pressure head at the top boundary and arbitrary initial conditions. In particular, nonlinearly increasing rainfall intensity at the surface boundary is considered. The result indicates that the coupling of seepage and deformation has a significant effect on the pressure-head profiles for the transient unsaturated seepage. The coupling effect is closely related to the boundary conditions. The coupling effect almost disappears if ponding at the ground surface occurs. The ponding time is different under the coupled and uncoupled conditions. There is a quick change in the pressure-head profiles near the time of ponding or peak or discontinuous rain in...

The use of electrical conductivity measurements in the prediction of hydraulic conductivity of unsaturated soils

Summary Statistical models have been widely used in soil science, hydrogeology and geotechnical engineering to predict the hydraulic conductivity of unsaturated soils. However, no effective method is available yet for the determination of the associated model parameters such as the tortuosity factor q. Considering the analogy between water flow and electrical current flow in a porous medium, in this study, we proposed to improve the predictive capability of statistical models by determining the tortuosity factor q using electrical conductivity (EC) measurements. We first developed a theoretical hydraulic–electrical conductivity (K–EC) relationship for unsaturated soils based on the bundle of capillary tubes model. This K–EC relationship was then used to form a new unsaturated soil EC model, which was verified using published experimental data. The tortuosity factor q can then be determined by fitting the new EC model to soil EC measurements. Experimental data of six soils were used to test the effectiveness of this method and it was shown that the prediction was significantly improved when compared with the one using the commonly suggested value q = 0.5. The associated root-mean-square-deviation (RMSD) between measurements and predictions is only 0.28 when q is obtained by using our proposed method. In contrast, the RMSD is 0.97 when q is simply assumed as 0.5.

Investigating the relationship between unsaturated hydraulic conductivity curve and confined compression curve

• Confined compression curve was related to hydraulic conductivity curve, closely. • Using confined compression curve parameters improved the precision of PTFs. • Using σ mc and σ i as inputs improved the estimation of hydraulic conductivity. • Gompertz model of compression curve can be related to the hydraulic conductivity. This study was conducted to estimate the soil unsaturated hydraulic conductivity through the van Genuchten model using easy to measure soil properties by regression and artificial neural networks methods. In this study, 148 soil samples were taken from five provinces of Iran. Basic soil properties (clay, silt/sand and bulk density) and other soil properties were measured. Soil water retention curve was measured to obtain the unsaturated hydraulic conductivity curve using the van Genuchten–Mualem model. Confined compression curve was measured and the modified model of van Genuchten was fitted on its data. Two-thirds and one-third of the data were used for the training and testing steps, respectively. Confined compression curve parameters and other soil properties were used as predictors to estimate unsaturated hydraulic conductivity curve. Pedotransfer functions (PTFs) were developed in two separate parts: in 5 and 6 PTFs basic soil properties were or were not used as predictors, respectively. The artificial neural networks (ANNs) performed better than the regression methods. Among the ANN-developed PTFs which have not used basic soil properties as predictors, PTF a3 , with the inputs of the parameters of confined compression curve ( n ∗ , α ∗ and e 0 ), performed better than the others. Also, among the ANN-developed PTFs that used basic soil properties as predictors along with the other input variables, PTF b5 that used the σ mc (stress at the maximum curvature) and σ i (stress at the inflection point) as inputs along with basic soil properties, performed better than the other PTFs. The results showed a successful prediction of the hydraulic conductivity curve using confined compression curve.

Application of EM38 and ERT methods in estimation of saturated hydraulic conductivity in unsaturated soil

Soil apparent electrical conductivity is being considerably used as a surrogate measure for soil properties and hydraulic parameters. In this study, measurements of electrical conductivity were accomplished with electrical resistivity tomography (ERT) and EM38 to develop multiple datasets for defining spatiotemporal moisture content variations and estimating saturated hydraulic conductivity under natural conditions in an experimental site located in Lisbon, Portugal. In addition, EM38 capability in monitoring electrical conductivity variations in comparison with ERT method was examined. In order to achieve these objectives, appropriate relationships were derived based on determination of experimental curve resistivity vs. degree of saturation by in-situ investigation to convert electrical resistivity maps inferred from ERT and EM38 data to moisture content distribution maps. In addition, the surface temperature variations during the experiment were measured and the effects of the temperature variations were removed by assuming 2% change in electrical resistivity per °C change in temperature. The conducted experiment proves that the soil is fairly homogenous and semi-pervious sediment and the spatiotemporal moisture content variations during the experiment barely exceed 10%. Our calculations constrain the range of saturated hydraulic conductivity to be 3–9 (cm/day) range.

Multimedial Study Guide of Field Hydropedological Measurements

Soil hydropedological data measured in situ provide an essential base for basic and also applied research in hydrological, water management, landscape and environmental disciplines. Quality of the measured data is a critical value determining the quality of results and derived conclusions. The knowledge and practical experience of the technician performing the measurements is presenting the human factor, which affects the quality of measured data most. The Multimedial Study Guide of Field Hydropedological Measurements (further referred to as “the Guide”) was created to present and explain selected field measurements determining soil physical and hydro-physical properties in a comprehensive, didactical and user-friendly way. The following topics are introduced: i) Soil sampling (disturbed and undisturbed soil samples), ii) Soil moisture content measurement using indirect non-destructive methods, iii) Determination of tensiometric soil water potential, iv) Measurement of saturated soil hydraulic conductivity in-situ with available groundwater level in measured layer and without available groundwater level in measured layer, v) Measurement of unsaturated soil hydraulic conductivity, and vi) Basic presentation of lysimetry. The Guide was for students, and also for academic workers and other interested members of the public. The English version enables everyone to use these guidelines and carry out each particular measurement, as well as evaluate and present the measured data correctly. The students of the Czech University of Life Sciences Prague use this Guide as a regular learning material in subjects dealing with soil and water relationship since 2012. Now, the 2nd revised edition is presented. The Guide is available on the internet (http://hydropedologie.agrobiologie.cz) and DVD (on request).

A test of the Beerkan Estimation of Soil Transfer parameters (BEST) procedure

The Beerkan Estimation of Soil Transfer parameters (BEST) procedure is attractive for a simple soil hydraulic characterization but testing the ability of this procedure to estimate soil properties is necessary. The BEST predictions were compared with soil water retention and hydraulic conductivity data measured in the laboratory and the field, respectively, at ten Sicilian field sites. Provided that BEST yielded physically possible scale parameters of the soil characteristic curves in most of the four replicated infiltration runs at a site, the measured water retention was satisfactorily predicted (i.e., not statistically significant differences between measurements and predictions, significant correlation between the data, regression line not significantly different from the identity one) when i) the infiltration run was relatively short (11 applied volumes of water); ii) the n shape parameter of the water retention curve was estimated on the basis of the measured sand and clay content of the soil; and iii) the saturated soil water content, θs, was set equal to 93% of the porosity. Possible field saturated soil hydraulic conductivity values were also obtained, although some trace of soil disturbance by the infiltration run was detected. The predicted unsaturated soil hydraulic conductivity was higher than the measured one, probably because the unimodal hydraulic conductivity function used in BEST does not reproduce the changes in the pore system of a real soil in the pressure head range close to saturation. It was concluded that BEST is promising to simply yield a reasonably reliable soil hydraulic characterization. An improved description of the unsaturated hydraulic conductivity function is desirable.

Solution of AntiSeepage for Mengxi River Based on Numerical Simulation of Unsaturated Seepage

Lessening the leakage of surface water can reduce the waste of water resources and ground water pollution. To solve the problem that Mengxi River could not store water enduringly, geology investigation, theoretical analysis, experiment research, and numerical simulation analysis were carried out. Firstly, the seepage mathematical model was established based on unsaturated seepage theory; secondly, the experimental equipment for testing hydraulic conductivity of unsaturated soil was developed to obtain the curve of two-phase flow. The numerical simulation of leakage in natural conditions proves the previous inference and leakage mechanism of river. At last, the seepage control capacities of different impervious materials were compared by numerical simulations. According to the engineering actuality, the impervious material was selected. The impervious measure in this paper has been proved to be effectible by hydrogeological research today.

高压实黄土非饱和土水运动试验模拟研究

对于压实度大于90%的黄土，使用滤纸法研究土壤基质吸力同干密度和含水率之间的关系，使用水平入渗法研究非饱和土水扩散率同干密度和含水率之间的关系，使用竖管法研究土样毛细水上升规律，并使用GeoStudio软件进行数值模拟。试验和模拟结果表明：由于压实程度的不同将改变土壤孔隙的结构特征，对土壤的持水特性有较大的影响，基质吸力和非饱导水率的确定应该同时考虑含水量和密度两种因素；土壤的压实可以有效减缓毛细水的运动速度，压实度为98%、95%和93%的压实土柱，在105天后毛细上升高度分别为74 cm、80 cm和94 cm。Geostdio软件可以用于土基毛细水上升的模拟。 For loess whose compacted degree is above 90%, the relationship between matric suction and volumetric water content under different compaction conditions is studied by filter paper method, and the relationship between Soil water diffusivity and volumetric water content under different compaction conditions is studied by horizontal infiltration method. The capillary water upward law is studied by vertical tube method, and is simulated by GeoStudio. Results of the experiment and the simulation show that the soil pore structure characteristics is changed due to the different degree of compaction, and influences soil retention ability. Two factors including volumetric water content and density must be considered simultaneously in determining matrix suction and unsaturated soil hydraulic conductivity. With increasing soil compacted degree, the speed of capillarity water movement is decreased. After 105 days, the rising heights of capillary water in soil column are 74 cm, 80 cm and 94 cm in the condition of compacted degree 98%, 95% and 93%, and GeoStudio could be used to simulate capillary water rise.

A study on unsaturated hydraulic conductivity of hill soil of north-east India

Hill slope hydrology in terms of surface drainage and infiltration is important for analysing its stability and understanding the possibility of landslides. The infiltrating water during rainfall is found to cause instability to the slope. The location of water table will be low in such hill slopes and the soil will be mostly unsaturated. Therefore, the subsurface drainage of infiltrating water in a slope is influenced by the unsaturated hydraulic conductivity (ku ) of soil. The hill slopes of north-east India mainly constitute unsaturated red soil. There are not many studies related to the determination of unsaturated hydraulic conductivity of this soil. Direct experimental determination of ku is a challenging task and requires costly and skilled experimentation. Therefore, the normal practice is to obtain ku based on water retention characteristic (WRC) and saturated hydraulic conductivity (ks ) of the soil. In this study, an equitensiometer, a matric potential sensor and a relative humidity sensor have been used to measure WRCs of hilly red soil. The study indicates that the measurement methodologies have significant influence on the uniqueness of WRC of red soil and, hence, the estimation of ku .

역해석기법을 이용한 불포화토 투수계수함수 산정에 관한 연구

Unsaturated hydraulic conductivity function is one of key parameters to solve the flow phenomena in problems of landslide. Prediction models for hydraulic conductivity function related to soil-water retention curve equations in many geotechnical applications have been still used instead of direct measurement of the hydraulic conductivity function since prediction models from soil-water retention curve equations are attractive for their fast and easy use and low cost. However, many researchers found that prediction models for the hydraulic conductivity function can not predict the hydraulic conductivity exactly in comparison with experimental outputs. This research introduced an inverse analysis to evaluate the hydraulic conductivity function corresponding to experimental output from the flow pump system. Optimisation process was carried out to obtain the hydraulic conductivity function. This research showed that the inverse analysis with flow pump system was suitable to assess the hydraulic conductivity in unsaturated soil, and the prediction models for the hydraulic conductivity were led to the significant discrepancy from actual experimental outputs.

Determination of saturated and unsaturated hydraulic conductivity using diviner 2000 capacitance probe

The estimation of hydraulic conductivity indicates how fluids flow through a substance and thus determine the water balance in the soil profile. In determining the saturated and unsaturated hydraulic conductivity of soil, five plots of 5.0 x 4.0 m were prepared with a PVC access tube installed in each plot. The plots were ponded profusely and surface covered with grass to prevent water loss by evaporation or water input by rain. The readings were taken twice daily for over a period of 5 days using capacitance probe with trade name Diviner 2000. The Diviner 2000 uses the method that utilizes the high dielectric constant of water compare to soil and air to determine water content of the soil. The trend lines of hydraulic conductivity has its linear regression r = 0.8296 - 0.9273 and its saturated hydraulic conductivity in the range of 5.09 cmh-1 – 14.03cmh-1 and unsaturated hydraulic conductivity in the range of 0.700 cmh-1 – 0.785 cmh-1. This reveals that soil water content can be obtained reasonably well from a capacitance probe which will allow for a determination of the pattern and use of the referred soil.

Laboratory measurement of hydraulic conductivity functions of two unsaturated sandy soils during drying and wetting processes

The importance of applying unsaturated soil mechanics to geotechnical engineering design has been well understood. However, the consumption of time and the necessity for a specific laboratory testing apparatus when measuring unsaturated soil properties have limited the application of unsaturated soil mechanics theories in practice. Although methods for predicting unsaturated soil properties have been developed, the verification of these methods for a wide range of soil types is required in order to increase the confidence of practicing engineers in using these methods. In this study, a new permeameter was developed to measure the hydraulic conductivity of unsaturated soils using the steady-state method and directly measured suction (negative pore-water pressure) values. The apparatus is instrumented with two tensiometers for the direct measurement of suction during the tests. The apparatus can be used to obtain the hydraulic conductivity function of sandy soil over a low suction range (0–10kPa). Firstly, the repeatability of the unsaturated hydraulic conductivity measurement, using the new permeameter, was verified by conducting tests on two identical sandy soil specimens and obtaining similar results. The hydraulic conductivity functions of the two sandy soils were then measured during the drying and wetting processes of the soils. A significant hysteresis was observed when the hydraulic conductivity was plotted against the suction. However, the hysteresis effects were not apparent when the conductivity was plotted against the volumetric water content. Furthermore, the measured unsaturated hydraulic conductivity functions were compared with predictions using three different predictive methods that are widely incorporated into numerical software. The results suggest that these predictive methods are capable of capturing the measured behavior with reasonable agreement.

Simplified estimation of unsaturated soil hydraulic conductivity using bulk electrical conductivity and particle size distribution

Unsaturated soil hydraulic conductivity K is a fundamental transfer property of soil but its measurement is costly, difficult, and time-consuming due to its large variations with water content (θ) or matric potential (h). Recently, C. Doussan and S. Ruy proposed a method/model using measurements of the electrical conductivity of soil core samples to predict K(h). This method requires the measurement or the setting of a range of matric potentials h in the core samples—a possible lengthy process requiring specialised devices. To avoid h estimation, we propose to simplify that method by introducing the particle-size distribution (PSD) of the soil as a proxy for soil pore diameters and matric potentials, with the Arya and Paris (AP) model. Tests of this simplified model (SM) with laboratory data on a broad range of soils and using the AP model with available, previously defined parameters showed that the accuracy was lower for the SM than for the original model (DR) in predicting K (RMSE of logK = 1.10 for SM v. 0.30 for DR; K in m s–1). However, accuracy was increased for SM when considering coarse- and medium-textured soils only (RMSE of logK = 0.61 for SM v. 0.26 for DR). Further tests with 51 soils from the UNSODA database and our own measurements, with estimated electrical properties, confirmed good agreement of the SM for coarse–medium-textured soils (<35–40% clay). For these textures, the SM also performed well compared with the van Genuchten–Mualem model. Error analysis of SM results and fitting of the AP parameter showed that most of the error for fine-textured soils came from poorer adequacy of the AP model’s previously defined parameters for defining the water retention curve, whereas this was much less so for coarse-textured soils. The SM, using readily accessible soil data, could be a relatively straightforward way to estimate, in situ or in the laboratory, K(h) for coarse–medium-textured soils. This requires, however, a prior check of the predictive efficacy of the AP model for the specific soil investigated, in particular for fine-textured/structured soils and when using previously defined AP parameters.

Effect of Net Stress on Hydraulic Conductivity of Unsaturated Soils

This note presents results of a laboratory test program that examines the influence of pore volumes on soil water coefficient of permeability in different saturation conditions. Comparing the results, it is observed that the dependency of water coefficient of permeability to void spaces in unsaturated soils follow a different trend than associated in saturated state. The shift of the soil–water characteristic curve within the change of pore spaces is utilized to qualify the opposite detected response of unsaturated water permeability to the change of pore spaces.