Groundwater

On the Groundwater page of the Project Settings dialog, RS3 offers different methods to establish groundwater pore pressure conditions in the model. The following options are available:

• None
• Phreatic Surfaces
• Steady State (finite element analysis)
• Transient (finite element analysis)

Phreatic Surfaces

When Phreatic Surfaces method is active, pore water pressures are assigned directly from the specified groundwater conditions (e.g., water table, pore water pressure grid, piezometric lines, or Ru coefficient). The pore pressure field is calculated using simple geometric interpolation relative to the defined water table, not by solving the flow equations.

Negative Pore Pressure Cutoff

In RS3, this parameter places an upper limit on the matric suction (negative pore pressure) considered in effective stress calculations. If a material-specific Negative Pore Pressure cutoff value value is defined in the material dialog, that value overrides the global project setting for the selected material.

This cutoff is only effective in Steady-State and Transient seepage analyses. When pore water pressures exceed the cutoff value, the suction used in effective stress computations is capped accordingly. This prevents unrealistic increases in shear strength or stiffness above the water table, where very high suctions may otherwise develop (e.g., in slope stability models).

Steady State (Finite Element Analysis)

If the Groundwater Method = Steady State then RS3 will allow you to model a steady-state finite element seepage analysis to determine the pore pressure distribution, based on the groundwater boundary conditions which you define for your model.

• The hydraulic boundary conditions are defined with the Add Groundwater Boundary Conditions option in the Groundwater menu.
• The hydraulic material properties are defined with the Define Hydraulic Properties option.

The seepage analysis can be used in conjunction with the stress analysis capability of RS3, or you may use the seepage analysis as a standalone groundwater analysis option, without necessarily computing a stress analysis.

See the Steady State Groundwater topic for more information.

Transient (Finite Element Analysis)

If the Groundwater Method = Transient then RS3 will allow you to model a transient finite element seepage analysis.

The input required for a Transient seepage analysis is the same as 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.

DEFINE INITIAL PWP METHOD BY STAGE

If this checkbox is selected, then you can define the initial pore water pressure at any stage, using any of the available groundwater methods (phreatic surfaces, steady state, or transient) on the Stages page of the Project Settings dialog.

ADVANCED GROUNDWATER OPTIONS

For Steady State or Transient groundwater, the following advanced analysis options can be customized by selecting the Advanced button.

Tolerance

The Tolerance represents the convergence criterion for the finite element seepage analysis. The solution is considered acceptable, when the difference in hydraulic head between iterations, at all nodes of the mesh, is less than the Tolerance.

Maximum Number of Iterations

The Maximum Number of Iterations allowed for the finite element seepage analysis. If the Tolerance is not achieved within the Maximum Number of Iterations, then the analysis will be terminated at the Maximum Number of Iterations.

Pore Fluid Unit Weight

The Pore Fluid Unit Weight is used for the calculation of pore pressure if the Groundwater Method is set to one of the following options:

• Phreatic Surfaces,
• Steady State,
• or Transient

The default value of the Pore Fluid Unit Weight is determined by the Units selected under the Units tab in Project Settings. The default value may be changed as required.