The options under the Groundwater tab in the Project Settings dialog, allow you to specify how pore water pressure will be modeled, if you are including pore pressure in the stress analysis (i.e. effective stress analysis). The following options are available:
Piezometric Lines
Water Pressure Grid (Total Head)
Water Pressure Grid (Pressure Head)
Water Pressure Grid (Pore Pressure)
Finite Element Analysis
NOTE: if the Groundwater Method = Finite Element Analysis, then Phase2 will compute 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. See below for more details.
Piezometric Lines
If the Groundwater Method = Piezometric Lines, then the user may define one or more Piezometric Lines in order to define the groundwater pore pressure conditions. Note:
Piezometric Lines are created with the Add Piezometric Line option.
After Piezometric Lines are created, they must then be assigned to the desired materials, using the Define Hydraulic option.
See the Add Piezometric Line and Define Hydraulic Properties topics for details.
Water Pressure Grids
There are three options for defining a Water Pressure Grid in Phase2:
Grid (Total Head)
Grid (Pressure Head)
Grid (Pore Pressure)
If the Groundwater Method is set to one of these three options, a Water Pressure Grid can be created or read from a file, using the Water Pressure Grid option in the Groundwater menu. See the Water Pressure Grid topic for details.
Grid Interpolation
When a Water Pressure Grid is specified, an Interpolation Method must also be specified. The Interpolation Method is used to calculate the water pressure at any point in the soil or rock, from the values at the grid points. There are several different Interpolation Methods which are available in Phase2. See the Interpolation Method topic for details.
Finite Element Analysis
If the Groundwater Method = Finite Element Analysis, then Phase2 will compute 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 groundwater boundary conditions are specified with the Set Boundary Conditions option in the Groundwater menu.
The groundwater seepage analysis uses the same mesh as the stress analysis. The seepage analysis is always carried out before the stress analysis, so that the calculated pore pressures can be utilized by the stress analysis.
The Finite Element Analysis groundwater option in Phase2 is a very powerful option, and allows you to use Phase2 as a steady state, finite element seepage analysis program. The seepage analysis can be used in conjunction with the stress analysis capability of Phase2, or you may use the seepage analysis as a complete standalone analysis option, without necessarily computing a stress analysis. See the Compute Results For option described below.
For a tutorial which demonstrates the finite element seepage analysis capability in Phase2, see the Phase2 Tutorials page.
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.
Note: the Tolerance specified for the groundwater seepage analysis is completely independent of the Tolerance specified for the stress analysis in Project Settings.
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.
Note: the Maximum Number of Iterations specified for the groundwater seepage analysis is completely independent of the Maximum Number of Iterations specified for the stress analysis in Project Settings.
Compute
The Compute option allows the user to specify whether the finite element analysis will compute BOTH stress and seepage results, or only seepage results.
If Compute = Groundwater AND Stress, then both seepage and stress analysis will be carried out when Compute is selected. This is always the default selection. The seepage analysis is always carried out before the stress analysis, so that the calculated pore pressures can be utilized by the stress analysis to compute effective stress results.
If Compute = Groundwater Only, then ONLY the seepage analysis will be computed, the stress analysis will NOT be computed.
The purpose of this option is to allow the user to turn OFF the stress analysis computation, if only seepage results are required (Compute = Groundwater Only). This option is particularly useful if you are running several Phase2 files in batch mode, and you only require seepage results, or you wish to verify seepage results on multiple files, before running the stress analysis.
If you are only computing a single file, then you can alternatively use the Compute (groundwater only) option (in the toolbar or the Groundwater menu), to compute seepage results only. It is not necessary to use the Compute = Groundwater Only option in Project Settings if you are only computing a single file.
Pore Fluid Unit Weight
The calculated pore pressure is directly proportional to the Pore Fluid Unit Weight if the Groundwater Method is set to one of the following options:
Piezometric Lines
Grid (Total Head)
Grid (Pressure Head)
Finite Element Analysis
The Pore Fluid Unit Weight does NOT enter into the pore pressure calculations, if the Groundwater Method = Grid (Pore Pressure), since in this case, pore pressures are determined directly from the grid data.
The default value of the Pore Fluid Unit Weight is determined by the Units selected under the General tab in Project Settings. The default value may be changed as required.
NOTE: the Pore Fluid Unit Weight also determines the unit weight of ponded water for the Add Ponded Water Load option. This determines the load magnitude of the distributed loading due to ponded water.