# Define Hydraulic Properties

If you are performing a groundwater analysis, the Define Hydraulic Properties option is used to specify the permeability characteristics for your materials. Material permeability is required by the finite element analysis, in order to solve the groundwater problem (i.e. determine the flow and pressure distribution throughout the model).

NOTE:

- Hydraulic Properties can only be defined for finite element groundwater analysis (i.e. Groundwater Method = Steady State FEA or Advanced Groundwater = Transient in Project Settings).
- Also, the Analysis Mode must be set to
**Groundwater**(steady state or transient) so that the groundwater modeling options are available in the*Slide2*menu and toolbar. - In this case, the Define Hydraulic Properties option will be available in the toolbar and the
**Properties**menu. - The materials in the Define Hydraulic Properties dialog, correspond to the materials in the Define Material Properties dialog (i.e. the dialog in which you define the strength properties of your materials, when the Analysis Mode = Slope Stability).
- The material names and colours which appear in the Define Hydraulic Properties dialog, are those which are specified in the Define Material Properties dialog (the names and colours CANNOT be edited in the Define Hydraulic Properties dialog).

## Saturated Permeability

A saturated permeability, Ks, must always be specified for a material. However, note that:

- If you are using a User Defined Permeability Function (see below for details), then the saturated permeability is specified as the first point of the permeability function (i.e. permeability at matric suction = 0). In this case, the saturated permeability option, Ks, will be disabled.
- For all other permeability function models (i.e. Simple, van Genuchten etc), the saturated permeability Ks is enabled.

## Anisotropic Permeability Parameters

Anisotropic permeability may be specified for a material (i.e. permeability varies with direction), by specifying a Factor and Angle, which defines the relative permeability in two orthogonal directions.

**K2 / K1**is the factor which specifies the relative permeability in the direction orthogonal to the K1 direction. NOTE that the K1 permeability is the "primary" permeability defined by the Saturated Permeability Ks, and the unsaturated permeability model you have defined in the dialog.**K1 Angle**is the angle which specifies the direction of the K1 permeability. The K1 Angle is specified relative to the positive X (horizontal) direction, as indicated by the picture in the dialog.

EXAMPLE: if K2 / K1 = 0.5 and K1 Angle = 0, then the permeability in the HORIZONTAL direction = Ks (in the saturated zone), and the permeability in the VERTICAL direction = 0.5 * Ks (in the saturated zone).

The following models are available in *Slide2* for describing the permeability in the unsaturated zone as a function of matric suction.

- Brooks and Corey
- Fredlund and Xing
- Gardner
- Simple
- van Genuchten
- user defined

A user-defined function can be defined by selecting the New button. See below for details about each model.

*Plot button*

After entering the parameters for the selected model, you can select the **Plot** button to view the actual permeability function which is defined by the model and the parameters you have entered.

*Pick button*

If you select the **Pick** button in the dialog, you will see another dialog, from which you can select from a list of materials, with representative parameters for the selected model. (References for the data are provided in the dialog). If you select OK in this dialog, the currently selected parameters will be automatically loaded into the Define Hydraulic Properties dialog.

## Simple

With the **Simple** model, an unsaturated permeability function is automatically determined by *Slide2* based on the magnitude of the saturated permeability Ks and the selected Soil Type. To view the function determined by *Slide2*, you can select the **Plot** button in the dialog. For the Simple model, you can choose one of the following Soil Types:

- General
- Sand
- Silt
- Clay
- Loam

For the General soil type, the unsaturated permeability simply decreases by an order of magnitude within the initial range of matric suction values, and then remains constant for higher values of suction.

For specific soil types (Sand, Silt, Clay or Loam) average curves have been determined from typical literature values.

## Brooks and Corey

The following equations define the **Brooks-Corey** permeability function (Brooks and Corey, 1964):

For :

Eqn.1a

For :

Eqn.1b

where: = Pore size index

= bubbling pressure

= matric suction

K = permeability

Ks = saturated permeability

## Fredlund and Xing

The following equation defines the **Fredlund-Xing** permeability function (Fredlund and Xing, 1994):

Eqn.2

where: A, B and C are the model parameters

= 2.7182818 â€¦

= matric suction

K = permeability

Ks = saturated permeability

## Gardner

The following equation defines the **Gardner** permeability function (Gardner, 1956):

Eqn.3

where: a and n are the model parameters

h = pressure head (suction)

K = permeability

Ks = saturated permeability

## Van Genuchten

The following equations define the **van Genuchten** permeability function (van Genuchten, 1980):

Eqn.4a

Eqn.4b

where: = degree of saturation

h = pressure head (suction)

are the model parameters

K = permeability

Ks = saturated permeability

NOTE: the parameters m and n are related as follows:

Eqn. 4c

However, you can specify a value of m which is independent from n, by selecting the **Custom m** checkbox, and entering a value for m.

For complete flexibility in defining permeability functions, a User Defined Permeability Function can be defined as follows:

NOTE: the data points on the graph can be moved graphically by clicking on them with the mouse and dragging.

**Name**of the User Defined Permeability Function you have defined will now appear in the

**Model**drop-list. It can be selected at any time, just like any of the other permeability models.

*Edit*

To modify an existing User Defined Permeability Function, select the Name of the function from the Model list, and select the **Edit** button. You can then edit the data which defines the function, in the User Defined Permeability Function dialog.

*Delete*

To delete an existing User Defined Permeability Function, select the Name of the function from the Model list, and select the **Delete** button.

*Copy*

To create a copy of an existing User Defined Permeability Function, select the Name of the function from the Model list, and select the **Copy** button. Enter a new name in the dialog which appears, and select OK. A new function will automatically be created, and the Name will appear in the Model list.

*Import / Export*

User Defined Permeability Functions in *Slide2* can be saved in their own separate file, if desired.

- To save a User Defined Permeability Function file, select the
**Export**button in the User Defined Permeability Function dialog. These files have a .FN5 filename extension. - To import a User Defined Permeability Function file, select the
**Import**button in the User Defined Permeability Function dialog.

- To save a User Defined Permeability Function file, select the