Groundwater Overview

The groundwater options in RS3 allow you to determine pore pressures which can be incorporated into the stress analysis to compute values of effective stress. Furthermore, if you choose finite element seepage analysis (steady state or transient) a seepage analysis can be carried out to compute pore pressures as well as flow rates and other hydraulic quantities.

To model groundwater in RS3:

1. First select the desired Groundwater Method in the Project Settings dialog. There are 3 options available:
• Phreatic Surface
• Steady State Finite element seepage analysis
• Transient Finite element seepage analysis
2. Use the applicable options (see below for details) to define the groundwater conditions for your model.

Phreatic Surface

If the Groundwater Method = Phreatic Surface:

1. Water surfaces are created with the Add Water By Surface or Add Water by Location options in the Groundwater menu.
2. PWP point sets are defined with the Add PWP Point Set option in the Groundwater menu.
3. Additional parameters for defining the phreatic surface, such as a constant pore water pressure or an Ru value can be defined with the Add Hydraulic Parameter from the Define Hydraulic Properties option.
4. Phreatic surface are then assigned to the desired materials and the staging sequence defined with the Define Hydraulic Properties option in the Groundwater menu or Material Properties dialog.

Steady State Finite Element Seepage Analysis

If the Groundwater Method = Steady State:

1. The hydraulic boundary conditions are defined with the Add Groundwater Boundary Conditions option in the Groundwater menu.
2. The hydraulic material properties are defined with the Define Hydraulic Properties option in the Groundwater menu.
3. Optional - if you wish to compute the steady-state flow volume across a surface, use the Add Discharge Section option in the Groundwater menu to define a discharge section.
4. Optional - if you wish to compute the seepage analysis only (without computing the stress analysis), then you can use the Compute (groundwater only) option. This allows you to view and verify the seepage analysis results, before proceeding to the stress analysis.

With finite element seepage analysis, the seepage analysis is used to calculate pore pressures for an effective stress analysis, just as with the Phreatic Surfaces options. It can also be used as a standalone groundwater option, independently of the stress analysis in RS3 (i.e. you can run a seepage analysis without necessarily computing a stress analysis). Flow rates, hydraulic gradients and other quantities can be computed, in addition to pore pressure.

Transient Finite Element Seepage Analysis

If the Groundwater Method = Transient:

• The input required for a Transient seepage analysis is the same as outlined above for a Steady State analysis, with some additional parameters required to define Transient time staging, boundary conditions and material parameters.

See the Transient Groundwater topic for more information.

Discharge Sections

If the Groundwater Method = Steady State or Transient finite element seepage analysis, then you can define discharge sections to compute groundwater flow rate across user-defined sections. See the Add Discharge Section topic.