Define Hydraulic (Seepage Analysis)

The options in the Define Hydraulic Properties dialog correspond to the Groundwater Method specified in the Project Settings menu. If Groundwater Method = Finite Element Analysis is selected, the permeability characteristics can be defined for each material.

These permeability characteristics are necessary for finite element analysis to solve the seepage problem (i.e. determine the flow and pore pressure distribution throughout the model). Available parameters are described below, and users can choose a distribution type for each.

Additionally, users can select a Permeability Model for characteristics in the unsaturated zone, see the topic for details. The Permeability Model is set to Simple by default.

Distribution Types

RS2 allows spatial distributions for permeability parameters (except for mv). Six distribution types are provided:

1. Constant
   • define a constant value
2. Mean Stress
   • define tabular values with respect to mean stress
3. Vertical Stress
   • define tabular values with respect to vertical stress
4. Horizontal Stress
   • define tabular values with respect to horizontal stress
5. Volumetric Strain
   • define tabular values with respect to volumetric strain
6. Coordinate
   • define tabular values with respect to X and Y coordinates

The default setting is Constant. For non-constant distributions, the applied values interpolated from the distribution tables can be viewed as contours in RS2 Interpret after computation. See the Data Contours topic for details.

Account for Water Content in Compressibility

The Account for Water Content in Compressibility option is only applicable to a coupled groundwater analysis (i.e., Consolidation Option = Coupled (Biot) under the Solver Options page in Project Settings dialog).

If this option is ON, the compressibility matrix will consider the water content which is especially useful for unsaturated soils. If this option is OFF, a fully-saturated condition is assumed when calculating the compressibility matrix. The setting is ON by default.

• When Unsaturated Behavior = None or Unsaturated Shear Strength in the Strength tab, the option is available.
• When Unsaturated Behavior = Single Effective Stress, the option is hidden and the water content in compressibility is always accounted.

Legacy Models

This option applies to models created with version 11.024 and after. For older models, the following settings will be applied to replicate the compressibility matrix calculations in old versions:

• If you open models saved in version 11.023, this option will be ON, since water content was always considered.
• If you open models saved in version 11.022 and earlier, this option will be OFF, since fully-saturated condition was always assumed.

Saturated Permeability

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

• If you are using a User Defined permeability model, then the saturated permeability is specified by both the first point of the permeability function (i.e. permeability at matric suction = 0), and the Relative Ks distribution (optional).
• 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).

• K1 Surface option allows the user to assign an anisotropic surface (created in Boundary menu) to the K1 angle.

Water Content

The water content values OR degree of saturation values must be defined when the Groundwater Method = Finite Element Analysis (Steady State or Transient) in the Project Settings dialog. They are used to define the Soil Water Characteristic Curves (SWCC) when computing unsaturated soil permeabilities.

• WC sat: the saturated water content. It must be greater than WC res, and not greater than porosity.
• WC res: the residual water content, which the gradient becomes zero (where is the volumetric water content).

For the Constant permeability model, you can define a WC curve slope. The degree of saturation values remains constant at 1, and the water content is simply calculated as WC =degree of saturation * porosity.

For the User Defined permeability model, the water content OR degree of saturation values are based on the user input data and the optional Relative WC. The first water content value is assumed as WC sat, and the last one is WC res. See the Permeability Models topic for more details.

Degree of Saturation

Similar to water content values, degree of saturation values can be defined alternatively. The residual degree of saturation and maximum degree of saturation need to be inputted. The relationship between water content and degree of saturation is:

Where is the porosity, is the residual water content, is the residual degree of saturation, is the saturated water content, is the maximum degree of saturation.

Mv

Mv is the coefficient of water volume change. The mv parameter input is available when the Groundwater Method = Finite Element Analysis (Steady State or Transient) in the Project Settings dialog. Note that this option will not be available for coupled consolidation analysis (i.e., when Consolidation Option = Coupled (Biot), mv is intrinsically calculated from the method, see the Coupled Consolidation manual for details).

In RS2, the mv parameter can be inputted with four options:

1. None
   • a constant value is calculated as the slope of water content curve at zero matric suction and is capped at 0.002.
2. Constant
   • user inputs a constant value.
3. Fluid
   • only fluid is considered.
4. 1D Elastic consolidation
   • 1D elastic uncoupled consolidation is considered.
5. 2D Elastic consolidation
   • 2D plane-strain elastic uncoupled consolidation is considered.

Stage Hydraulic Properties

For a multi-stage model, hydraulic properties can be staged in the Stage Factors tab, under the Stage Hydraulic properties and Stage Hydraulic Distributions categories. See the Stage Factors topic for more information.