Simulating transient infiltration in unsaturated soils

1998 ◽  
Vol 35 (6) ◽  
pp. 1093-1100 ◽  
Author(s):  
J R McDougall ◽  
I C Pyrah
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Flow Model ◽  
Unsaturated Flow ◽  
Surface Region ◽  
Infiltration Rate ◽  
Soil Suction ◽  
Wetting Front ◽  
Near Surface ◽  
Unsaturated Hydraulic Conductivity

Transient responses to various infiltration events have been examined using an unsaturated flow model. Numerical simulations reveal a range of infiltration patterns which can be related to the ratio of infiltration rate to unsaturated hydraulic conductivity. A high value of this ratio reflects a prevailing hydraulic conductivity which cannot readily redistribute the newly infiltrated moisture. Moisture accumulates in the near-surface region before advancing down through the soil as a distinct wetting front. In contrast, low values of the ratio of rainfall to unsaturated hydraulic conductivity show minimal moisture accumulation, as the relatively small volumes of infiltrating moisture are readily redistributed through the soil profile.Key words: numerical modelling, infiltration, unsaturated soil, soil suction, groundwater.

Historical development of soil-water physics and solute transport in porous media

2007 ◽  
Vol 7 (1) ◽  
pp. 59-66 ◽  
Author(s):  
D.E. Rolston
Keyword(s):  
Porous Media ◽  
Hydraulic Conductivity ◽  
Solute Transport ◽  
Soil Water ◽  
20Th Century ◽  
Water Flow ◽  
Unsaturated Soils ◽  
Transport Processes ◽  
Transport In Porous Media ◽  
Unsaturated Hydraulic Conductivity

The science of soil-water physics and contaminant transport in porous media began a little more than a century ago. The first equation to quantify the flow of water is attributed to Darcy. The next major development for unsaturated media was made by Buckingham in 1907. Buckingham quantified the energy state of soil water based on the thermodynamic potential energy. Buckingham then introduced the concept of unsaturated hydraulic conductivity, a function of water content. The water flux as the product of the unsaturated hydraulic conductivity and the total potential gradient has become the accepted Buckingham-Darcy law. Two decades later, Richards applied the continuity equation to Buckingham's equation and obtained a general partial differential equation describing water flow in unsaturated soils. For combined water and solute transport, it had been recognized since the latter half of the 19th century that salts and water do not move uniformly. It wasn't until the middle of the 20th century that scientists began to understand the complex processes of diffusion, dispersion, and convection and to develop mathematical formulations for solute transport. Knowledge on water flow and solute transport processes has expanded greatly since the early part of the 20th century to the present.

Estimation of hydraulic conductivity of unsaturated soils using a geotechnical centrifuge

2002 ◽  
Vol 39 (3) ◽  
pp. 684-694 ◽  
Author(s):  
D N Singh ◽  
Sneha J Kuriyan
Keyword(s):  
Hydraulic Conductivity ◽  
Water Content ◽  
Soil Sample ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Soil Hydraulic Conductivity ◽  
Centrifuge Testing ◽  
Geotechnical Centrifuge ◽  
Silty Soil ◽  
Unsaturated Hydraulic Conductivity

A saturated silty soil sample is centrifuged in a geotechnical centrifuge to create an unsaturated state. The change in water content of the soil sample is recorded at different points along the length of the sample to obtain the water-content profile, which is then used to obtain the unsaturated hydraulic conductivity of the soil sample. These hydraulic conductivity values are compared with those obtained and reported by previous researchers by conducting accelerated falling-head tests on this soil sample in a centrifuge. The study demonstrates the use of centrifugation techniques to obtain hydraulic conductivities of unsaturated soils.Key words: silty soil, saturated soil, unsaturated soil, hydraulic conductivity, centrifuge testing.

Improved measurement of conductivity on swelling clay soils using a modified disc permeameter method

Soil Research ◽  
2006 ◽  
Vol 44 (7) ◽  
pp. 701 ◽  
Author(s):  
J. L. Foley ◽  
P. E. Tolmie ◽  
D. M. Silburn
Keyword(s):  
Steady State ◽  
Unsaturated Soils ◽  
Strongly Correlated ◽  
Internal Drainage ◽  
Wetting Front ◽  
Steady State Flow ◽  
State Flow ◽  
Modified Method ◽  
Swelling Clays ◽  
Unsaturated Hydraulic Conductivity

Disc permeameters are the preferred method for measuring unsaturated hydraulic conductivity (Kψ) in situ. However, in swelling clays, Kψ measured using 3-D measurement and analysis methods are often several orders of magnitude too high and are of no value for modelling internal drainage. During a series of experiments, the causes of inflated Kψ values were identified and a modified method developed to accurately measure Kψ. On a Black Vertosol, Kψ was strongly correlated with water content and measurement period, with higher flow rates occurring until the soil profile had fully wet up. Near-saturated Kψ measured under permeameters was up to 2 orders of magnitude higher than field-saturated conductivity (KFS) measured in ponded rings. This discrepancy was caused by residual capillarity and unrestricted swelling at the wetting front in unsaturated soils. In addition, lateral flow was common and surface depressions around permeameters filled with water, erroneously contributing to measured infiltration and invalidating assumptions in the 3-D analysis. To prevent this, permeameters were confined within rings to restrict flow to 1D, and measured Kψ (confined) was then compared with Kψ (unconfined) and KFS (ponded rings). Confining flow to 1D reduced Kψ by up to 2 orders of magnitude for a Black Vertosol and by a factor of 3 for a Red Ferrosol. Near-saturated Kψ from confined permeameters agreed well with KFS after similar short measurement durations (e.g. 0.5 h), but Kψ was still overestimated until steady-state flow was established. Therefore, to derive estimates of Kψ that reflect natural flow during internal drainage, we recommend (i) pre-wetting the soil and extending measurement time to attain steady-state flow, and (ii) confining permeameters within rings to restrict flow to 1 dimension. This method was used to compare lucerne ley and annual cropping treatments on 2 Black Vertosols (Bongeen and Waco). Kψ was similar between cropping treatments, suggesting that initial differences in structure and porosity were transient and related to soil moisture content. The Bongeen soil had a significantly lower Kψ (K–1 cm of 0.8 mm/h) than the Waco soil (2.0 mm/h).

Unsaturated hydraulic conductivity of vineyard soils with high rock fragment content in the Mosel area, Germany

2021 ◽  
Author(s):  
Selina Walle ◽  
Thomas Iserloh ◽  
Manuel Seeger
Keyword(s):  
Hydraulic Conductivity ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Unsaturated Soils ◽  
Hydrological Cycle ◽  
Calculated Data ◽  
Rock Fragment ◽  
Unsaturated Hydraulic Conductivity ◽  
Significant Difference

<p>The study deals with the unsaturated hydraulic conductivity of soils within the scope of the Diverfarming-Project, funded by the EU commission (Horizon 2020 grant agreement no 728003). For this reason, the field work took place in the examined vineyard of the Wawerner Jesuitenberg near Kanzem in the Saar-Mosel valley (Rhineland-Palatinate, Germany). The mentioned parameter is one of the most important specific factors of the hydrological cycle to characterize soil hydraulic properties in the unsaturated soil zone. A mini disc infiltrometer was used to measure the conductivity values at different suctions. The purpose of this study is to determine the plausibility of the fundamentals and the analytical expression of the unsaturated conductivity models in a nearly skeletal soil of schist. In this regard, the mathematical expressions of Mualem (1976), van Genuchten (1980) and Zhang (1997) are focused on calculating the unsaturated hydraulic conductivity. The two variables α and n are analysed in order to better compare between literature specifications and the explicit calculated data of the vineyard’s soil. As a result, the various developments of α are similar thus the significant difference is based on the value of n. Nevertheless, in consideration of these frame conditions the models represent a suitable mathematical expression of the unsaturated hydraulic conductivity. Furthermore, a range of parameters affecting this conductivity is analysed, particularly with regard to the applied variable soil and cultivation management under the grapevines in the vineyard. Also, the rock fragment cover and the pore size distribution are taken into account. In this context the soil compaction and modified pore size distribution in the wheel tracks stand out due to salient unsaturated hydraulic conductivities at higher tensions. In particular, the stone cover of the contact surface influence the characteristics of the analysed conductivity. Additionally, the connection of stone cover, management and pore size distribution creates a mixture of affected parameters of the unsaturated hydraulic conductivity.</p><p> </p><p>Mualem, Y.: A new model for predicting the hydraulic conductivity of unsaturated porous media, Water Resour. Res, 12, 513–522, https://doi.org/10.1029/WR012i003p00513, 1976.</p><p>Van Genuchten, M.T.: A Closed-form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils, Soil Sci. Soc. Am. J., 44, 892–898, https://doi.org/10.2136/sssaj1980.03615995004400050002x, 1980.</p><p>Zhang, R.: Determination of Soil Sorptivity and Hydraulic Conductivity from the Disk Infiltrometer, Soil Sci. Soc. Am. J., 61, 1024–1030, https://doi.org/10.2136/sssaj1997.03615995006100040005x, 1997.</p>

Suction Stress in Unsaturated Soils Considering Hydraulic Hysteresis

2020 ◽  
pp. 110-123
Author(s):  
J. Ramírez Jiménez ◽  
J. M. Horta Rangel ◽  
M. L. Pérez Rea ◽  
E. Rojas González ◽  
T. Lopez Lara ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Time Lag ◽  
Degree Of Saturation ◽  
Soil Suction ◽  
Two Dimensional ◽  
Suction Stress ◽  
Hydraulic Hysteresis ◽  
Transient Thermal ◽  
Over Time

Aims: To develop a flow-moisture model that allows determining the variation of suction over time, as well as the suction stresses, using the finite element method in a two-dimensional model of unsaturated soil through an analogy with a transient thermal problem. Study Design: The variables used in this study were soil suction, hydraulic conductivity, diffusivity and degree of saturation which was represented as the  parameter of the Bishop’s effective stress equation. Place and Duration of Study: Graduate Engineering Department, Universidad Autónoma de Querétaro, between November 2019 and August 2020. Methodology: To establish the model, experimental Soil-Water Retention Curve was taken from Galaviz (2016). With this information, the curves of hydraulic conductivity and diffusivity were calculated with the methods of Fredlund et al. (2012) and Li (1996). In ANSYS 19.2, an analogous transient thermal analysis was run to determine suction changes over time in a 12 x 2.4 meters two-dimensional medium with an impermeable membrane at the center of its surface which was 4.8 meters long. Through these suction changes, the hydraulic hysteresis algorithm presented by Zhou et al. (2012) was used to calculate the respective degrees of saturation, which were considered as the  parameter to obtain the suction stresses. Results: The changes in soil suction, degree of saturation and suction stress were properly modeled. Conclusion: When considering the hydraulic hysteresis cycles, both spatial and temporal variations behaved in a similar way in the  parameters as well as in the suction stresses. Such stresses depended on the analysis period, increasing in the dry season, according to the precipitation-evapotranspiration model, and decreasing in the wetting season. A time lag was observed between the maximum and minimum stresses as greater depths were studied. Along the horizontal axis, considering the same depth, the stresses varied more in the areas adjacent to the impermeable membrane, while at the center this variation was practically null.

scholarly journals A Fractal Approach for Predicting Unsaturated Hydraulic Conductivity of Deformable Clay

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Gaoliang Tao ◽  
Xueliang Zhu ◽  
Jianchao Cai ◽  
Henglin Xiao ◽  
Qingsheng Chen ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Unsaturated Soils ◽  
Quantitative Description ◽  
Fractal Model ◽  
Reference State ◽  
Deformation Condition ◽  
Simple Method ◽  
Unsaturated Hydraulic Conductivity ◽  
Deformed State ◽  
Relative Hydraulic Conductivity

The relative hydraulic conductivity is one of the key parameters for unsaturated soils in numerous fields of geotechnical engineering. The quantitative description of its variation law is of significant theoretical and technical values. Parameters in a classical hydraulic conductivity model are generally complex; it is difficult to apply these parameters to predict and estimate the relative hydraulic conductivity under deformation condition. Based on the fractal theory, a simple method is presented in this study for predicting the relative hydraulic conductivity under deformation condition. From the experimental soil-water characteristic curve at a reference state, the fractal dimension and air-entry value are determined at a reference state. By using the prediction model of air-entry value, the air-entry values at the deformed state are then determined. With the two parameters determined, the relative hydraulic conductivity at the deformed state is predicted using the fractal model of relative hydraulic conductivity. The unsaturated hydraulic conductivity of deformable Hunan clay is measured by the instantaneous profile method. Values of relative hydraulic conductivity predicted by the fractal model are compared with those obtained from experimental measurements, which proves the rationality of the proposed prediction method.

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