Hydraulic Conductivity

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SVSoils

 

 

Knowing the coefficient of permeability (i.e., hydraulic conductivity) of a soil is vital to modeling the movement of water through saturated and unsaturated soils. Considerable effort has been expended to develop computer models capable of analyzing seepage through saturated/unsaturated soil systems. The movement of water through an unsaturated soil takes on the form of a function since its permeability varies with the degree of saturation of the soil. Determination of the hydraulic properties of an unsaturated soil is time consuming and expensive since several measurements must be made with the soil at various degrees of saturation.  Consequently, it has become quite acceptable in many cases to utilize simplified estimation methods for the prediction of the hydraulic conductivity of saturated/unsaturated soil systems.

 

An understanding of the hydraulic properties of unsaturated soils is critical when modeling complex seepage problems. The permeability function of a soil is related to the soil-water characteristic curve. As a result, the unsaturated permeability of a soil is commonly estimated based on the soil-water characteristic curve. SVSOILS provides the ability to both store unsaturated soil data as well as estimate the unsaturated soil permeability function which is related to soil suction. The software has implemented the management of saturated soil permeability data as well as a number of methods that can be used to estimate the saturated permeability of a soil.

 

Saturated Hydraulic Conductivity

The saturated hydraulic conductivity, ksat value is the hydraulic conductivity of the material in the x-direction when soil suction is zero (or the pore-water pressure is zero or positive).

 

ksat Options: SVSOILS software contains 15 ksat methods for estimating the saturated coefficient of permeability. However, the ksat methods shown in the drop list are those that have their required inputs entered into the software. The table below shows the required inputs for each ksat option. A description of these methods can be found in the sections below and in the SVSOILS Theory Manual.

 

Ksat Method

Required Input

Beyer (1964) ksat

D10, D60

Hazen's (1911) ksat

D10, D60

Kozeny (1989) ksat

Grain-size data

Kruger (1992) ksat

Grain-size data

Terzaghi (1981) ksat

D10

Zamarin (1992) ksat

Grain-size data

Fair-Hatch (1959) ksat

Grain-size data

NAVFAC ksat

D10

Chapuis (2003) ksat

D10

Rawls and Brakensiek (1983) ksat

USDA Sand Clay

Rawls and Brakensiek (1993) ksat

USDA Sand Clay

Slitcher (1962) ksat

D10

Kozeny-Carman (1989) ksat

Fredlund and Xing (1994) SWCC fit

Inverse ksat

Grain-size data, Fredlund and Xing (1994) SWCC fit

 

Constant ksat: The Constant ksat field displays the ksat value.

 

Unsaturated Hydraulic Conductivity

The Unsaturated Hydraulic Conductivity drop list contains the estimation methods that are currently implemented in the SVSOILS software.

 

The estimation methods provide a smooth representation of the saturated/unsaturated permeability (or hydraulic conductivity) curve. SVSOILS also allows for the input of laboratory data where linear interpolation is used to determine the permeability between measured laboratory data points. It should be noted that the interpolation procedure may not be ideal under some circumstances.

 

IfNone” is selected, the ksat value will be used to generate the unsaturated hydraulic conductivity function. If Laboratory Data is selected the data entered in the Laboratory Data section of the tab will be used.

 

Ksat vs Void Ratio

The Ksat vs Void Ratio method droplist contains all the methods currently implemented in SVSOILS for the fitting of laboratory data using mathematical equations. A description of these methods can be found in the following sections and in the  SVSOILS Theory Manual.

 

Related Links (Topics relating to this section):

Hydraulic Conductivity

Saturated Hydraulic Conductivity

Unsaturated Hydraulic Conductivity

Data vs Void Ratio

Single Power Function

Taylor Estimation