Under the Groundwater tab in the Project Settings dialog, you can include the effect of pore pressure in the consolidation analysis, by selecting the Groundwater Analysis checkbox.
This allows you to define a horizontal water table at any depth.
If your model is multi-stage, then you can specify the depth of the water table at each stage (i.e. you can raise or lower the water table).
When the Groundwater Analysis checkbox is selected, this enables all other groundwater modeling options in Settle3D. For an overview of groundwater modeling options in Settle3D, see the Groundwater Overview topic.
NOTE:
If you are modeling a time-dependent consolidation analysis, then you MUST select the Groundwater Analysis checkbox, because the modeling of pore pressure is essential for the time-dependent consolidation analysis (i.e. you must define the groundwater conditions, this is NOT optional).
If you are NOT modeling time-dependent consolidation, then you do not necessarily have to define groundwater (e.g. if you are only interested in immediate settlement or long term consolidation).
In future versions of Settle3D, more sophisticated groundwater modeling options should be available (e.g. import a 3-dimensional grid of pore pressure values). However, in this first version of the program, only the simple horizontal water table option is provided for modeling the initial groundwater pore pressure.
Water Table Depth
Water table depth is measured from the ground surface.
To define a water table at the ground surface, enter Depth = 0.
To define a water table at some depth below the ground surface, enter the Depth as a positive number.
To define a water table above the ground surface, enter the Depth as a negative number. In this case, it is assumed that the ground surface is submerged under a layer of ponded water, and the weight of the ponded water will be accounted for in the analysis. If embankment loads are defined, the buoyant unit weight will be used for the submerged portion of an embankment.
If your model uses multiple stages, the depth of the water table can be staged, by selecting the Depth varies with stage checkbox, and entering the depth at each stage.
Water Unit Weight
The water unit weight is used to calculate the initial pore pressure. The initial pore pressure at any point below the water table, is equal to the water unit weight multiplied by the vertical distance to the water table.
Generate excess pore pressure above water table
By default, the soil is assumed to be dry above the water table, so an applied load does not generate excess pore pressure above the water table.
If you want the soil to behave as if it were saturated above the water table, then you can select the Generate excess pore pressures above water table checkbox. If this checkbox is selected, applied loads will generate excess pore pressure above the water table, as if the material were saturated with B-bar = 1.
This option does NOT affect initial pore pressure calculations, only the calculation of excess pore pressure above the water table. Initial pore pressure above the water table is ALWAYS zero, regardless of the setting of this option.
NOTE: this option was introduced in version 1.005 of Settle3D. In versions 1.004 and earlier, excess pore pressure WAS CALCULATED ABOVE THE WATER TABLE. If Settle3D files from version 1.004 or earlier, are read into the current version, then the Generate excess pore pressures above water table checkbox will automatically be turned ON for these files, because this corresponds to the original analysis. If you wish to re-compute results for old files, then simply turn off this checkbox, and re-run the analysis.